Column and Data Types

Column and Data Types

SQLAlchemy provides abstractions for most common database data types, and a mechanism for specifying your own custom data types.

The methods and attributes of type objects are rarely used directly. Type objects are supplied to Table definitions and can be supplied as type hints to functions for occasions where the database driver returns an incorrect type.

>>> users = Table('users', metadata,
...               Column('id', Integer, primary_key=True),
...               Column('login', String(32))
...              )

SQLAlchemy will use the Integer and String(32) type information when issuing a CREATE TABLE statement and will use it again when reading back rows SELECTed from the database. Functions that accept a type (such as Column()) will typically accept a type class or instance; Integer is equivalent to Integer() with no construction arguments in this case.

Generic Types

Generic types specify a column that can read, write and store a particular type of Python data. SQLAlchemy will choose the best database column type available on the target database when issuing a CREATE TABLE statement. For complete control over which column type is emitted in CREATE TABLE, such as VARCHAR see SQL Standard and Multiple Vendor Types and the other sections of this chapter.

Object Name	Description
`BigInteger`	A type for bigger `int` integers.
`Boolean`	A bool datatype.
`Date`	A type for `datetime.date()` objects.
`DateTime`	A type for `datetime.datetime()` objects.
`Enum`	Generic Enum Type.
`Float`	Type representing floating point types, such as `FLOAT` or `REAL`.
`Integer`	A type for `int` integers.
`Interval`	A type for `datetime.timedelta()` objects.
`LargeBinary`	A type for large binary byte data.
`MatchType`	Refers to the return type of the MATCH operator.
`Numeric`	A type for fixed precision numbers, such as `NUMERIC` or `DECIMAL`.
`PickleType`	Holds Python objects, which are serialized using pickle.
`SchemaType`	Mark a type as possibly requiring schema-level DDL for usage.
`SmallInteger`	A type for smaller `int` integers.
`String`	The base for all string and character types.
`Text`	A variably sized string type.
`Time`	A type for `datetime.time()` objects.
`Unicode`	A variable length Unicode string type.
`UnicodeText`	An unbounded-length Unicode string type.

class sqlalchemy.types.``BigInteger

A type for bigger int integers.

Typically generates a BIGINT in DDL, and otherwise acts like a normal Integer on the Python side.

Class signature

class sqlalchemy.types.BigInteger (sqlalchemy.types.Integer)

class sqlalchemy.types.``Boolean(create_constraint=False, name=None, _create_events=True)

A bool datatype.

Boolean typically uses BOOLEAN or SMALLINT on the DDL side, and on the Python side deals in True or False.

The Boolean datatype currently has two levels of assertion that the values persisted are simple true/false values. For all backends, only the Python values None, True, False, 1 or 0 are accepted as parameter values. For those backends that don’t support a “native boolean” datatype, an option exists to also create a CHECK constraint on the target column

Changed in version 1.2: the Boolean datatype now asserts that incoming Python values are already in pure boolean form.

Class signature

class sqlalchemy.types.Boolean (sqlalchemy.types.Emulated, sqlalchemy.types.TypeEngine, sqlalchemy.types.SchemaType)

method sqlalchemy.types.Boolean.__init__(create_constraint=False, name=None, _create_events=True)

Construct a Boolean.
- Parameters
  - create_constraint –
    
    defaults to False. If the boolean is generated as an int/smallint, also create a CHECK constraint on the table that ensures 1 or 0 as a value.
    
    Note
    
    it is strongly recommended that the CHECK constraint have an explicit name in order to support schema-management concerns. This can be established either by setting the Boolean.name parameter or by setting up an appropriate naming convention; see Configuring Constraint Naming Conventions for background.
    
    Changed in version 1.4: - this flag now defaults to False, meaning no CHECK constraint is generated for a non-native enumerated type.
  - name – if a CHECK constraint is generated, specify the name of the constraint.

method sqlalchemy.types.Boolean.bind_processor(dialect)

Return a conversion function for processing bind values.

Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

If processing is not necessary, the method should return None.
- Parameters
  
  dialect – Dialect instance in use.
method sqlalchemy.types.Boolean.literal_processor(dialect)

Return a conversion function for processing literal values that are to be rendered directly without using binds.

This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

New in version 0.9.0.
attribute sqlalchemy.types.Boolean.python_type
method sqlalchemy.types.Boolean.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.``Date

A type for datetime.date() objects.

Class signature

class sqlalchemy.types.Date (sqlalchemy.types._LookupExpressionAdapter, sqlalchemy.types.TypeEngine)

method sqlalchemy.types.Date.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.
attribute sqlalchemy.types.Date.python_type

class sqlalchemy.types.``DateTime(timezone=False)

A type for datetime.datetime() objects.

Date and time types return objects from the Python datetime module. Most DBAPIs have built in support for the datetime module, with the noted exception of SQLite. In the case of SQLite, date and time types are stored as strings which are then converted back to datetime objects when rows are returned.

For the time representation within the datetime type, some backends include additional options, such as timezone support and fractional seconds support. For fractional seconds, use the dialect-specific datatype, such as TIME. For timezone support, use at least the TIMESTAMP datatype, if not the dialect-specific datatype object.

Class signature

class sqlalchemy.types.DateTime (sqlalchemy.types._LookupExpressionAdapter, sqlalchemy.types.TypeEngine)

method sqlalchemy.types.DateTime.__init__(timezone=False)

Construct a new DateTime.
- Parameters
  
  timezone – boolean. Indicates that the datetime type should enable timezone support, if available on the base date/time-holding type only. It is recommended to make use of the TIMESTAMP datatype directly when using this flag, as some databases include separate generic date/time-holding types distinct from the timezone-capable TIMESTAMP datatype, such as Oracle.
method sqlalchemy.types.DateTime.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.
attribute sqlalchemy.types.DateTime.python_type

class sqlalchemy.types.``Enum(\enums, **kw*)

Generic Enum Type.

The Enum type provides a set of possible string values which the column is constrained towards.

The Enum type will make use of the backend’s native “ENUM” type if one is available; otherwise, it uses a VARCHAR datatype. An option also exists to automatically produce a CHECK constraint when the VARCHAR (so called “non-native”) variant is produced; see the Enum.create_constraint flag.

The Enum type also provides in-Python validation of string values during both read and write operations. When reading a value from the database in a result set, the string value is always checked against the list of possible values and a LookupError is raised if no match is found. When passing a value to the database as a plain string within a SQL statement, if the Enum.validate_strings parameter is set to True, a LookupError is raised for any string value that’s not located in the given list of possible values; note that this impacts usage of LIKE expressions with enumerated values (an unusual use case).

Changed in version 1.1: the Enum type now provides in-Python validation of input values as well as on data being returned by the database.

The source of enumerated values may be a list of string values, or alternatively a PEP-435-compliant enumerated class. For the purposes of the Enum datatype, this class need only provide a __members__ method.

When using an enumerated class, the enumerated objects are used both for input and output, rather than strings as is the case with a plain-string enumerated type:

import enum
class MyEnum(enum.Enum):
    one = 1
    two = 2
    three = 3
t = Table(
    'data', MetaData(),
    Column('value', Enum(MyEnum))
)
connection.execute(t.insert(), {"value": MyEnum.two})
assert connection.scalar(t.select()) is MyEnum.two

Above, the string names of each element, e.g. “one”, “two”, “three”, are persisted to the database; the values of the Python Enum, here indicated as integers, are not used; the value of each enum can therefore be any kind of Python object whether or not it is persistable.

In order to persist the values and not the names, the Enum.values_callable parameter may be used. The value of this parameter is a user-supplied callable, which is intended to be used with a PEP-435-compliant enumerated class and returns a list of string values to be persisted. For a simple enumeration that uses string values, a callable such as lambda x: [e.value for e in x] is sufficient.

New in version 1.1: - support for PEP-435-style enumerated classes.

See also

ENUM - PostgreSQL-specific type, which has additional functionality.

ENUM - MySQL-specific type

Class signature

class sqlalchemy.types.Enum (sqlalchemy.types.Emulated, sqlalchemy.types.String, sqlalchemy.types.SchemaType)

method sqlalchemy.types.Enum.__init__(\enums, **kw*)

Construct an enum.

Keyword arguments which don’t apply to a specific backend are ignored by that backend.
- Parameters
  - *enums –
    
    either exactly one PEP-435 compliant enumerated type or one or more string or unicode enumeration labels. If unicode labels are present, the convert_unicode flag is auto-enabled.
    
    New in version 1.1: a PEP-435 style enumerated class may be passed.
  - convert_unicode –
    
    Enable unicode-aware bind parameter and result-set processing for this Enum’s data. This is set automatically based on the presence of unicode label strings.
    
    Deprecated since version 1.3: The Enum.convert_unicode parameter is deprecated and will be removed in a future release. All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary.
  - create_constraint –
    
    defaults to False. When creating a non-native enumerated type, also build a CHECK constraint on the database against the valid values.
    
    Note
    
    it is strongly recommended that the CHECK constraint have an explicit name in order to support schema-management concerns. This can be established either by setting the Enum.name parameter or by setting up an appropriate naming convention; see Configuring Constraint Naming Conventions for background.
    
    Changed in version 1.4: - this flag now defaults to False, meaning no CHECK constraint is generated for a non-native enumerated type.
  - metadata – Associate this type directly with a MetaData object. For types that exist on the target database as an independent schema construct (PostgreSQL), this type will be created and dropped within create_all() and drop_all() operations. If the type is not associated with any MetaData object, it will associate itself with each Table in which it is used, and will be created when any of those individual tables are created, after a check is performed for its existence. The type is only dropped when drop_all() is called for that Table object’s metadata, however.
  - name – The name of this type. This is required for PostgreSQL and any future supported database which requires an explicitly named type, or an explicitly named constraint in order to generate the type and/or a table that uses it. If a PEP-435 enumerated class was used, its name (converted to lower case) is used by default.
  - native_enum – Use the database’s native ENUM type when available. Defaults to True. When False, uses VARCHAR + check constraint for all backends. The VARCHAR length can be controlled with Enum.length
  - length –
    
    Allows specifying a custom length for the VARCHAR when Enum.native_enum is False. By default it uses the length of the longest value.
    
    New in version 1.3.16.
  - schema –
    
    Schema name of this type. For types that exist on the target database as an independent schema construct (PostgreSQL), this parameter specifies the named schema in which the type is present.
    
    Note
    
    The schema of the Enum type does not by default make use of the schema established on the owning Table. If this behavior is desired, set the inherit_schema flag to True.
  - quote – Set explicit quoting preferences for the type’s name.
  - inherit_schema – When True, the “schema” from the owning Table will be copied to the “schema” attribute of this Enum, replacing whatever value was passed for the schema attribute. This also takes effect when using the Table.to_metadata() operation.
  - validate_strings –
    
    when True, string values that are being passed to the database in a SQL statement will be checked for validity against the list of enumerated values. Unrecognized values will result in a LookupError being raised.
    
    New in version 1.1.0b2.
  - values_callable –
    
    A callable which will be passed the PEP-435 compliant enumerated type, which should then return a list of string values to be persisted. This allows for alternate usages such as using the string value of an enum to be persisted to the database instead of its name.
    
    New in version 1.2.3.
  - sort_key_function –
    
    a Python callable which may be used as the “key” argument in the Python sorted() built-in. The SQLAlchemy ORM requires that primary key columns which are mapped must be sortable in some way. When using an unsortable enumeration object such as a Python 3 Enum object, this parameter may be used to set a default sort key function for the objects. By default, the database value of the enumeration is used as the sorting function.
    
    New in version 1.3.8.

method sqlalchemy.types.Enum.create(bind=None, checkfirst=False)

inherited from the SchemaType.create() method of SchemaType

Issue CREATE DDL for this type, if applicable.
method sqlalchemy.types.Enum.drop(bind=None, checkfirst=False)

inherited from the SchemaType.drop() method of SchemaType

Issue DROP DDL for this type, if applicable.

class sqlalchemy.types.``Float(precision=None, asdecimal=False, decimal_return_scale=None)

Type representing floating point types, such as FLOAT or REAL.

This type returns Python float objects by default, unless the Float.asdecimal flag is set to True, in which case they are coerced to decimal.Decimal objects.

Note

The Float type is designed to receive data from a database type that is explicitly known to be a floating point type (e.g. FLOAT, REAL, others) and not a decimal type (e.g. DECIMAL, NUMERIC, others). If the database column on the server is in fact a Numeric type, such as DECIMAL or NUMERIC, use the Numeric type or a subclass, otherwise numeric coercion between float/Decimal may or may not function as expected.

Class signature

class sqlalchemy.types.Float (sqlalchemy.types.Numeric)

method sqlalchemy.types.Float.__init__(precision=None, asdecimal=False, decimal_return_scale=None)

Construct a Float.
- Parameters
  - precision – the numeric precision for use in DDL CREATE TABLE.
  - asdecimal – the same flag as that of Numeric, but defaults to False. Note that setting this flag to True results in floating point conversion.
  - decimal_return_scale –
    
    Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Note that the MySQL float types, which do include “scale”, will use “scale” as the default for decimal_return_scale, if not otherwise specified.
    
    New in version 0.9.0.

method sqlalchemy.types.Float.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.``Integer

A type for int integers.

Class signature

class sqlalchemy.types.Integer (sqlalchemy.types._LookupExpressionAdapter, sqlalchemy.types.TypeEngine)

method sqlalchemy.types.Integer.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.
method sqlalchemy.types.Integer.literal_processor(dialect)

Return a conversion function for processing literal values that are to be rendered directly without using binds.

This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

New in version 0.9.0.
attribute sqlalchemy.types.Integer.python_type

class sqlalchemy.types.``Interval(native=True, second_precision=None, day_precision=None)

A type for datetime.timedelta() objects.

The Interval type deals with datetime.timedelta objects. In PostgreSQL, the native INTERVAL type is used; for others, the value is stored as a date which is relative to the “epoch” (Jan. 1, 1970).

Note that the Interval type does not currently provide date arithmetic operations on platforms which do not support interval types natively. Such operations usually require transformation of both sides of the expression (such as, conversion of both sides into integer epoch values first) which currently is a manual procedure (such as via expression.func).

Class signature

class sqlalchemy.types.Interval (sqlalchemy.types.Emulated, sqlalchemy.types._AbstractInterval, sqlalchemy.types.TypeDecorator)

method sqlalchemy.types.Interval.__init__(native=True, second_precision=None, day_precision=None)

Construct an Interval object.
- Parameters
  - native – when True, use the actual INTERVAL type provided by the database, if supported (currently PostgreSQL, Oracle). Otherwise, represent the interval data as an epoch value regardless.
  - second_precision – For native interval types which support a “fractional seconds precision” parameter, i.e. Oracle and PostgreSQL
  - day_precision – for native interval types which support a “day precision” parameter, i.e. Oracle.

method sqlalchemy.types.Interval.adapt_to_emulated(impltype, \*kw*)

Given an impl class, adapt this type to the impl assuming “emulated”.

The impl should also be an “emulated” version of this type, most likely the same class as this type itself.

e.g.: sqltypes.Enum adapts to the Enum class.
method sqlalchemy.types.Interval.bind_processor(dialect)

Return a conversion function for processing bind values.

Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

If processing is not necessary, the method should return None.
- Parameters
  
  dialect – Dialect instance in use.
attribute sqlalchemy.types.Interval.impl

alias of sqlalchemy.sql.sqltypes.DateTime
attribute sqlalchemy.types.Interval.python_type
method sqlalchemy.types.Interval.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.``LargeBinary(length=None)

A type for large binary byte data.

The LargeBinary type corresponds to a large and/or unlengthed binary type for the target platform, such as BLOB on MySQL and BYTEA for PostgreSQL. It also handles the necessary conversions for the DBAPI.

Class signature

class sqlalchemy.types.LargeBinary (sqlalchemy.types._Binary)

method sqlalchemy.types.LargeBinary.__init__(length=None)

Construct a LargeBinary type.
- Parameters
  
  length – optional, a length for the column for use in DDL statements, for those binary types that accept a length, such as the MySQL BLOB type.

class sqlalchemy.types.``MatchType(create_constraint=False, name=None, _create_events=True)

Refers to the return type of the MATCH operator.

As the ColumnOperators.match() is probably the most open-ended operator in generic SQLAlchemy Core, we can’t assume the return type at SQL evaluation time, as MySQL returns a floating point, not a boolean, and other backends might do something different. So this type acts as a placeholder, currently subclassing Boolean. The type allows dialects to inject result-processing functionality if needed, and on MySQL will return floating-point values.

New in version 1.0.0.

Class signature

class sqlalchemy.types.MatchType (sqlalchemy.types.Boolean)

class sqlalchemy.types.``Numeric(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

A type for fixed precision numbers, such as NUMERIC or DECIMAL.

This type returns Python decimal.Decimal objects by default, unless the Numeric.asdecimal flag is set to False, in which case they are coerced to Python float objects.

Note

The Numeric type is designed to receive data from a database type that is explicitly known to be a decimal type (e.g. DECIMAL, NUMERIC, others) and not a floating point type (e.g. FLOAT, REAL, others). If the database column on the server is in fact a floating-point type, such as FLOAT or REAL, use the Float type or a subclass, otherwise numeric coercion between float/Decimal may or may not function as expected.

Note

The Python decimal.Decimal class is generally slow performing; cPython 3.3 has now switched to use the cdecimal library natively. For older Python versions, the cdecimal library can be patched into any application where it will replace the decimal library fully, however this needs to be applied globally and before any other modules have been imported, as follows:

import sys
import cdecimal
sys.modules["decimal"] = cdecimal

Note that the cdecimal and decimal libraries are not compatible with each other, so patching cdecimal at the global level is the only way it can be used effectively with various DBAPIs that hardcode to import the decimal library.

Class signature

class sqlalchemy.types.Numeric (sqlalchemy.types._LookupExpressionAdapter, sqlalchemy.types.TypeEngine)

method sqlalchemy.types.Numeric.__init__(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

Construct a Numeric.
- Parameters
  - precision – the numeric precision for use in DDL CREATE TABLE.
  - scale – the numeric scale for use in DDL CREATE TABLE.
  - asdecimal – default True. Return whether or not values should be sent as Python Decimal objects, or as floats. Different DBAPIs send one or the other based on datatypes - the Numeric type will ensure that return values are one or the other across DBAPIs consistently.
  - decimal_return_scale –
    
    Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Types which do include an explicit “.scale” value, such as the base Numeric as well as the MySQL float types, will use the value of “.scale” as the default for decimal_return_scale, if not otherwise specified.
    
    New in version 0.9.0.

When using the `Numeric` type, care should be taken to ensure that the asdecimal setting is appropriate for the DBAPI in use - when Numeric applies a conversion from Decimal-&gt;float or float-&gt; Decimal, this conversion incurs an additional performance overhead for all result columns received.
DBAPIs that return Decimal natively (e.g. psycopg2) will have better accuracy and higher performance with a setting of `True`, as the native translation to Decimal reduces the amount of floating- point issues at play, and the Numeric type itself doesn’t need to apply any further conversions. However, another DBAPI which returns floats natively *will* incur an additional conversion overhead, and is still subject to floating point data loss - in which case `asdecimal=False` will at least remove the extra conversion overhead.

method sqlalchemy.types.Numeric.bind_processor(dialect)

Return a conversion function for processing bind values.

Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

If processing is not necessary, the method should return None.
- Parameters
  
  dialect – Dialect instance in use.
method sqlalchemy.types.Numeric.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.
method sqlalchemy.types.Numeric.literal_processor(dialect)

Return a conversion function for processing literal values that are to be rendered directly without using binds.

This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

New in version 0.9.0.
attribute sqlalchemy.types.Numeric.python_type
method sqlalchemy.types.Numeric.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.``PickleType(protocol=4, pickler=None, comparator=None)

Holds Python objects, which are serialized using pickle.

PickleType builds upon the Binary type to apply Python’s pickle.dumps() to incoming objects, and pickle.loads() on the way out, allowing any pickleable Python object to be stored as a serialized binary field.

To allow ORM change events to propagate for elements associated with PickleType, see Mutation Tracking.

Class signature

class sqlalchemy.types.PickleType (sqlalchemy.types.TypeDecorator)

method sqlalchemy.types.PickleType.__init__(protocol=4, pickler=None, comparator=None)

Construct a PickleType.
- Parameters
  - protocol – defaults to pickle.HIGHEST_PROTOCOL.
  - pickler – defaults to cPickle.pickle or pickle.pickle if cPickle is not available. May be any object with pickle-compatible dumps and loads methods.
  - comparator – a 2-arg callable predicate used to compare values of this type. If left as None, the Python “equals” operator is used to compare values.

method sqlalchemy.types.PickleType.bind_processor(dialect)

Provide a bound value processing function for the given Dialect.

This is the method that fulfills the TypeEngine contract for bound value conversion. TypeDecorator will wrap a user-defined implementation of process_bind_param() here.

User-defined code can override this method directly, though its likely best to use process_bind_param() so that the processing provided by self.impl is maintained.
- Parameters
  
  dialect – Dialect instance in use.
This method is the reverse counterpart to the result_processor() method of this class.
method sqlalchemy.types.PickleType.compare_values(x, y)

Given two values, compare them for equality.

By default this calls upon TypeEngine.compare_values() of the underlying “impl”, which in turn usually uses the Python equals operator ==.

This function is used by the ORM to compare an original-loaded value with an intercepted “changed” value, to determine if a net change has occurred.
attribute sqlalchemy.types.PickleType.impl

alias of sqlalchemy.sql.sqltypes.LargeBinary
method sqlalchemy.types.PickleType.result_processor(dialect, coltype)

Provide a result value processing function for the given Dialect.

This is the method that fulfills the TypeEngine contract for result value conversion. TypeDecorator will wrap a user-defined implementation of process_result_value() here.

User-defined code can override this method directly, though its likely best to use process_result_value() so that the processing provided by self.impl is maintained.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – A SQLAlchemy data type

This method is the reverse counterpart to the [`bind_processor()`](#sqlalchemy.types.PickleType.bind_processor "sqlalchemy.types.PickleType.bind_processor") method of this class.

class sqlalchemy.types.``SchemaType(name=None, schema=None, metadata=None, inherit_schema=False, quote=None, _create_events=True)

Mark a type as possibly requiring schema-level DDL for usage.

Supports types that must be explicitly created/dropped (i.e. PG ENUM type) as well as types that are complimented by table or schema level constraints, triggers, and other rules.

SchemaType classes can also be targets for the DDLEvents.before_parent_attach() and DDLEvents.after_parent_attach() events, where the events fire off surrounding the association of the type object with a parent Column.

See also

Enum

Boolean

Class signature

class sqlalchemy.types.SchemaType (sqlalchemy.sql.expression.SchemaEventTarget)

method sqlalchemy.types.SchemaType.adapt(impltype, \*kw*)
attribute sqlalchemy.types.SchemaType.bind
method sqlalchemy.types.SchemaType.copy(\*kw*)
method sqlalchemy.types.SchemaType.create(bind=None, checkfirst=False)

Issue CREATE DDL for this type, if applicable.
method sqlalchemy.types.SchemaType.drop(bind=None, checkfirst=False)

Issue DROP DDL for this type, if applicable.

class sqlalchemy.types.``SmallInteger

A type for smaller int integers.

Typically generates a SMALLINT in DDL, and otherwise acts like a normal Integer on the Python side.

Class signature

class sqlalchemy.types.SmallInteger (sqlalchemy.types.Integer)

class sqlalchemy.types.``String(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

The base for all string and character types.

In SQL, corresponds to VARCHAR. Can also take Python unicode objects and encode to the database’s encoding in bind params (and the reverse for result sets.)

The length field is usually required when the String type is used within a CREATE TABLE statement, as VARCHAR requires a length on most databases.

Class signature

class sqlalchemy.types.String (sqlalchemy.types.Concatenable, sqlalchemy.types.TypeEngine)

attribute sqlalchemy.types.String.RETURNS_BYTES = symbol(‘RETURNS_BYTES’)
attribute sqlalchemy.types.String.RETURNS_CONDITIONAL = symbol(‘RETURNS_CONDITIONAL’)
attribute sqlalchemy.types.String.RETURNS_UNICODE = symbol(‘RETURNS_UNICODE’)
attribute sqlalchemy.types.String.RETURNS_UNKNOWN = symbol(‘RETURNS_UNKNOWN’)
method sqlalchemy.types.String.__init__(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

Create a string-holding type.
- Parameters
  - length – optional, a length for the column for use in DDL and CAST expressions. May be safely omitted if no CREATE TABLE will be issued. Certain databases may require a length for use in DDL, and will raise an exception when the CREATE TABLE DDL is issued if a VARCHAR with no length is included. Whether the value is interpreted as bytes or characters is database specific.
  - collation –
    
    Optional, a column-level collation for use in DDL and CAST expressions. Renders using the COLLATE keyword supported by SQLite, MySQL, and PostgreSQL. E.g.:
```
>>> from sqlalchemy import cast, select, String
>>> print(select(cast('some string', String(collation='utf8'))))
SELECT CAST(:param_1 AS VARCHAR COLLATE utf8) AS anon_1
```
  - convert_unicode –
    
    When set to True, the String type will assume that input is to be passed as Python Unicode objects under Python 2, and results returned as Python Unicode objects. In the rare circumstance that the DBAPI does not support Python unicode under Python 2, SQLAlchemy will use its own encoder/decoder functionality on strings, referring to the value of the create_engine.encoding parameter parameter passed to create_engine() as the encoding.
    
    Deprecated since version 1.3: The String.convert_unicode parameter is deprecated and will be removed in a future release. All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary.
    
    For the extremely rare case that Python Unicode is to be encoded/decoded by SQLAlchemy on a backend that does natively support Python Unicode, the string value "force" can be passed here which will cause SQLAlchemy’s encode/decode services to be used unconditionally.
    
    Note
    
    SQLAlchemy’s unicode-conversion flags and features only apply to Python 2; in Python 3, all string objects are Unicode objects. For this reason, as well as the fact that virtually all modern DBAPIs now support Unicode natively even under Python 2, the String.convert_unicode flag is inherently a legacy feature.
    
    Note
    
    In the vast majority of cases, the Unicode or UnicodeText datatypes should be used for a Column that expects to store non-ascii data. These datatypes will ensure that the correct types are used on the database side as well as set up the correct Unicode behaviors under Python 2.
    
    See also
    
    create_engine.convert_unicode - Engine-wide parameter
  - unicode_error –
    
    Optional, a method to use to handle Unicode conversion errors. Behaves like the errors keyword argument to the standard library’s string.decode() functions, requires that String.convert_unicode is set to "force"
    
    Deprecated since version 1.3: The String.unicode_errors parameter is deprecated and will be removed in a future release. This parameter is unnecessary for modern Python DBAPIs and degrades performance significantly.

method sqlalchemy.types.String.bind_processor(dialect)

Return a conversion function for processing bind values.

Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

If processing is not necessary, the method should return None.
- Parameters
  
  dialect – Dialect instance in use.
method sqlalchemy.types.String.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.
method sqlalchemy.types.String.literal_processor(dialect)

Return a conversion function for processing literal values that are to be rendered directly without using binds.

This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

New in version 0.9.0.
attribute sqlalchemy.types.String.python_type
method sqlalchemy.types.String.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.``Text(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

A variably sized string type.

In SQL, usually corresponds to CLOB or TEXT. Can also take Python unicode objects and encode to the database’s encoding in bind params (and the reverse for result sets.) In general, TEXT objects do not have a length; while some databases will accept a length argument here, it will be rejected by others.

Class signature

class sqlalchemy.types.Text (sqlalchemy.types.String)

class sqlalchemy.types.``Time(timezone=False)

A type for datetime.time() objects.

Class signature

class sqlalchemy.types.Time (sqlalchemy.types._LookupExpressionAdapter, sqlalchemy.types.TypeEngine)

method sqlalchemy.types.Time.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.
attribute sqlalchemy.types.Time.python_type

class sqlalchemy.types.``Unicode(length=None, \*kwargs*)

A variable length Unicode string type.

The Unicode type is a String subclass that assumes input and output as Python unicode data, and in that regard is equivalent to the usage of the convert_unicode flag with the String type. However, unlike plain String, it also implies an underlying column type that is explicitly supporting of non-ASCII data, such as NVARCHAR on Oracle and SQL Server. This can impact the output of CREATE TABLE statements and CAST functions at the dialect level, and can also affect the handling of bound parameters in some specific DBAPI scenarios.

The encoding used by the Unicode type is usually determined by the DBAPI itself; most modern DBAPIs feature support for Python unicode objects as bound values and result set values, and the encoding should be configured as detailed in the notes for the target DBAPI in the Dialects section.

For those DBAPIs which do not support, or are not configured to accommodate Python unicode objects directly, SQLAlchemy does the encoding and decoding outside of the DBAPI. The encoding in this scenario is determined by the encoding flag passed to create_engine().

When using the Unicode type, it is only appropriate to pass Python unicode objects, and not plain str. If a plain str is passed under Python 2, a warning is emitted. If you notice your application emitting these warnings but you’re not sure of the source of them, the Python warnings filter, documented at http://docs.python.org/library/warnings.html, can be used to turn these warnings into exceptions which will illustrate a stack trace:

import warnings
warnings.simplefilter('error')

For an application that wishes to pass plain bytestrings and Python unicode objects to the Unicode type equally, the bytestrings must first be decoded into unicode. The recipe at Coercing Encoded Strings to Unicode illustrates how this is done.

See also

UnicodeText - unlengthed textual counterpart to Unicode.

Class signature

class sqlalchemy.types.Unicode (sqlalchemy.types.String)

method sqlalchemy.types.Unicode.__init__(length=None, \*kwargs*)

Create a Unicode object.

Parameters are the same as that of String, with the exception that convert_unicode defaults to True.

class sqlalchemy.types.``UnicodeText(length=None, \*kwargs*)

An unbounded-length Unicode string type.

See Unicode for details on the unicode behavior of this object.

Like Unicode, usage the UnicodeText type implies a unicode-capable type being used on the backend, such as NCLOB, NTEXT.

Class signature

class sqlalchemy.types.UnicodeText (sqlalchemy.types.Text)

method sqlalchemy.types.UnicodeText.__init__(length=None, \*kwargs*)

Create a Unicode-converting Text type.

Parameters are the same as that of TextClause, with the exception that convert_unicode defaults to True.

SQL Standard and Multiple Vendor Types

This category of types refers to types that are either part of the SQL standard, or are potentially found within a subset of database backends. Unlike the “generic” types, the SQL standard/multi-vendor types have no guarantee of working on all backends, and will only work on those backends that explicitly support them by name. That is, the type will always emit its exact name in DDL with CREATE TABLE is issued.

Object Name	Description
`ARRAY`	Represent a SQL Array type.
`BIGINT`	The SQL BIGINT type.
`BINARY`	The SQL BINARY type.
`BLOB`	The SQL BLOB type.
`BOOLEAN`	The SQL BOOLEAN type.
`CHAR`	The SQL CHAR type.
`CLOB`	The CLOB type.
`DATE`	The SQL DATE type.
`DATETIME`	The SQL DATETIME type.
`DECIMAL`	The SQL DECIMAL type.
`FLOAT`	The SQL FLOAT type.
`INT`	alias of `sqlalchemy.sql.sqltypes.INTEGER`
`INTEGER`	The SQL INT or INTEGER type.
`JSON`	Represent a SQL JSON type.
`NCHAR`	The SQL NCHAR type.
`NUMERIC`	The SQL NUMERIC type.
`NVARCHAR`	The SQL NVARCHAR type.
`REAL`	The SQL REAL type.
`SMALLINT`	The SQL SMALLINT type.
`TEXT`	The SQL TEXT type.
`TIME`	The SQL TIME type.
`TIMESTAMP`	The SQL TIMESTAMP type.
`VARBINARY`	The SQL VARBINARY type.
`VARCHAR`	The SQL VARCHAR type.

class sqlalchemy.types.``ARRAY(item_type, as_tuple=False, dimensions=None, zero_indexes=False)

Represent a SQL Array type.

Note

This type serves as the basis for all ARRAY operations. However, currently only the PostgreSQL backend has support for SQL arrays in SQLAlchemy. It is recommended to use the PostgreSQL-specific sqlalchemy.dialects.postgresql.ARRAY type directly when using ARRAY types with PostgreSQL, as it provides additional operators specific to that backend.

ARRAY is part of the Core in support of various SQL standard functions such as array_agg which explicitly involve arrays; however, with the exception of the PostgreSQL backend and possibly some third-party dialects, no other SQLAlchemy built-in dialect has support for this type.

An ARRAY type is constructed given the “type” of element:

mytable = Table("mytable", metadata,
        Column("data", ARRAY(Integer))
    )

The above type represents an N-dimensional array, meaning a supporting backend such as PostgreSQL will interpret values with any number of dimensions automatically. To produce an INSERT construct that passes in a 1-dimensional array of integers:

connection.execute(
        mytable.insert(),
        data=[1,2,3]
)

The ARRAY type can be constructed given a fixed number of dimensions:

mytable = Table("mytable", metadata,
        Column("data", ARRAY(Integer, dimensions=2))
    )

Sending a number of dimensions is optional, but recommended if the datatype is to represent arrays of more than one dimension. This number is used:

When emitting the type declaration itself to the database, e.g. INTEGER[][]
When translating Python values to database values, and vice versa, e.g. an ARRAY of Unicode objects uses this number to efficiently access the string values inside of array structures without resorting to per-row type inspection
When used with the Python getitem accessor, the number of dimensions serves to define the kind of type that the [] operator should return, e.g. for an ARRAY of INTEGER with two dimensions:
```
>>> expr = table.c.column[5]  # returns ARRAY(Integer, dimensions=1)
>>> expr = expr[6]  # returns Integer
```

For 1-dimensional arrays, an ARRAY instance with no dimension parameter will generally assume single-dimensional behaviors.

SQL expressions of type ARRAY have support for “index” and “slice” behavior. The Python [] operator works normally here, given integer indexes or slices. Arrays default to 1-based indexing. The operator produces binary expression constructs which will produce the appropriate SQL, both for SELECT statements:

select(mytable.c.data[5], mytable.c.data[2:7])

as well as UPDATE statements when the Update.values() method is used:

mytable.update().values({
    mytable.c.data[5]: 7,
    mytable.c.data[2:7]: [1, 2, 3]
})

The ARRAY type also provides for the operators Comparator.any() and Comparator.all(). The PostgreSQL-specific version of ARRAY also provides additional operators.

New in version 1.1.0.

See also

sqlalchemy.dialects.postgresql.ARRAY

Class signature

class sqlalchemy.types.ARRAY (sqlalchemy.sql.expression.SchemaEventTarget, sqlalchemy.types.Indexable, sqlalchemy.types.Concatenable, sqlalchemy.types.TypeEngine)

class Comparator(expr)

Define comparison operations for ARRAY.

More operators are available on the dialect-specific form of this type. See Comparator.

Class signature

class sqlalchemy.types.ARRAY.Comparator (sqlalchemy.types.Comparator, sqlalchemy.types.Comparator)
- method sqlalchemy.types.ARRAY.Comparator.all(other, operator=None)
  
  Return other operator ALL (array) clause.
  
  Argument places are switched, because ALL requires array expression to be on the right hand-side.
  
  E.g.:
```
from sqlalchemy.sql import operators
conn.execute(
    select(table.c.data).where(
            table.c.data.all(7, operator=operators.lt)
        )
)
```
  Parameters
  - other – expression to be compared
  - operator – an operator object from the sqlalchemy.sql.operators package, defaults to eq().
  See also
  
  all_()
  
  Comparator.any()
- method sqlalchemy.types.ARRAY.Comparator.any(other, operator=None)
  
  Return other operator ANY (array) clause.
  
  Argument places are switched, because ANY requires array expression to be on the right hand-side.
  
  E.g.:
```
from sqlalchemy.sql import operators
conn.execute(
    select(table.c.data).where(
            table.c.data.any(7, operator=operators.lt)
        )
)
```
  Parameters
  - other – expression to be compared
  - operator – an operator object from the sqlalchemy.sql.operators package, defaults to eq().
  See also
  
  any_()
  
  Comparator.all()
- method sqlalchemy.types.ARRAY.Comparator.contains(\arg, **kw*)
  
  Implement the ‘contains’ operator.
  
  Produces a LIKE expression that tests against a match for the middle of a string value:
```
column LIKE '%' || <other> || '%'
```
  E.g.:
```
stmt = select(sometable).\
    where(sometable.c.column.contains("foobar"))
```
  Since the operator uses LIKE, wildcard characters "%" and "_" that are present inside the <other> expression will behave like wildcards as well. For literal string values, the ColumnOperators.contains.autoescape flag may be set to True to apply escaping to occurrences of these characters within the string value so that they match as themselves and not as wildcard characters. Alternatively, the ColumnOperators.contains.escape parameter will establish a given character as an escape character which can be of use when the target expression is not a literal string.
  
  Parameters
  - other – expression to be compared. This is usually a plain string value, but can also be an arbitrary SQL expression. LIKE wildcard characters % and _ are not escaped by default unless the ColumnOperators.contains.autoescape flag is set to True.
  - autoescape –
    
    boolean; when True, establishes an escape character within the LIKE expression, then applies it to all occurrences of "%", "_" and the escape character itself within the comparison value, which is assumed to be a literal string and not a SQL expression.
    
    An expression such as:
```
somecolumn.contains("foo%bar", autoescape=True)
```
    Will render as:
```
somecolumn LIKE '%' || :param || '%' ESCAPE '/'
```
    With the value of :param as "foo/%bar".
  - escape –
    
    a character which when given will render with the ESCAPE keyword to establish that character as the escape character. This character can then be placed preceding occurrences of % and _ to allow them to act as themselves and not wildcard characters.
    
    An expression such as:
```
somecolumn.contains("foo/%bar", escape="^")
```
    Will render as:
```
somecolumn LIKE '%' || :param || '%' ESCAPE '^'
```
    The parameter may also be combined with ColumnOperators.contains.autoescape:
```
somecolumn.contains("foo%bar^bat", escape="^", autoescape=True)
```
    Where above, the given literal parameter will be converted to "foo^%bar^^bat" before being passed to the database.
  See also
  
  ColumnOperators.startswith()
  
  ColumnOperators.endswith()
  
  ColumnOperators.like()
method sqlalchemy.types.ARRAY.__init__(item_type, as_tuple=False, dimensions=None, zero_indexes=False)

Construct an ARRAY.

E.g.:
```
Column('myarray', ARRAY(Integer))
```
Arguments are:
- Parameters
  - item_type – The data type of items of this array. Note that dimensionality is irrelevant here, so multi-dimensional arrays like INTEGER[][], are constructed as ARRAY(Integer), not as ARRAY(ARRAY(Integer)) or such.
  - as_tuple=False – Specify whether return results should be converted to tuples from lists. This parameter is not generally needed as a Python list corresponds well to a SQL array.
  - dimensions – if non-None, the ARRAY will assume a fixed number of dimensions. This impacts how the array is declared on the database, how it goes about interpreting Python and result values, as well as how expression behavior in conjunction with the “getitem” operator works. See the description at ARRAY for additional detail.
  - zero_indexes=False – when True, index values will be converted between Python zero-based and SQL one-based indexes, e.g. a value of one will be added to all index values before passing to the database.

attribute sqlalchemy.types.ARRAY.comparator_factory

alias of sqlalchemy.sql.sqltypes.ARRAY.Comparator
method sqlalchemy.types.ARRAY.compare_values(x, y)

Compare two values for equality.
attribute sqlalchemy.types.ARRAY.hashable

Flag, if False, means values from this type aren’t hashable.

Used by the ORM when uniquing result lists.
attribute sqlalchemy.types.ARRAY.python_type
attribute sqlalchemy.types.ARRAY.zero_indexes = False

If True, Python zero-based indexes should be interpreted as one-based on the SQL expression side.

class sqlalchemy.types.``BIGINT

The SQL BIGINT type.

Class signature

class sqlalchemy.types.BIGINT (sqlalchemy.types.BigInteger)

class sqlalchemy.types.``BINARY(length=None)

The SQL BINARY type.

Class signature

class sqlalchemy.types.BINARY (sqlalchemy.types._Binary)

class sqlalchemy.types.``BLOB(length=None)

The SQL BLOB type.

Class signature

class sqlalchemy.types.BLOB (sqlalchemy.types.LargeBinary)

class sqlalchemy.types.``BOOLEAN(create_constraint=False, name=None, _create_events=True)

The SQL BOOLEAN type.

Class signature

class sqlalchemy.types.BOOLEAN (sqlalchemy.types.Boolean)

class sqlalchemy.types.``CHAR(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

The SQL CHAR type.

Class signature

class sqlalchemy.types.CHAR (sqlalchemy.types.String)

class sqlalchemy.types.``CLOB(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

The CLOB type.

This type is found in Oracle and Informix.

Class signature

class sqlalchemy.types.CLOB (sqlalchemy.types.Text)

class sqlalchemy.types.``DATE

The SQL DATE type.

Class signature

class sqlalchemy.types.DATE (sqlalchemy.types.Date)

class sqlalchemy.types.``DATETIME(timezone=False)

The SQL DATETIME type.

Class signature

class sqlalchemy.types.DATETIME (sqlalchemy.types.DateTime)

class sqlalchemy.types.``DECIMAL(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

The SQL DECIMAL type.

Class signature

class sqlalchemy.types.DECIMAL (sqlalchemy.types.Numeric)

class sqlalchemy.types.``FLOAT(precision=None, asdecimal=False, decimal_return_scale=None)

The SQL FLOAT type.

Class signature

class sqlalchemy.types.FLOAT (sqlalchemy.types.Float)

attribute sqlalchemy.types..sqlalchemy.types.``INT

alias of sqlalchemy.sql.sqltypes.INTEGER

class sqlalchemy.types.``JSON(none_as_null=False)

Represent a SQL JSON type.

Note

JSON is provided as a facade for vendor-specific JSON types. Since it supports JSON SQL operations, it only works on backends that have an actual JSON type, currently:

PostgreSQL - see sqlalchemy.dialects.postgresql.JSON and sqlalchemy.dialects.postgresql.JSONB for backend-specific notes
MySQL - see sqlalchemy.dialects.mysql.JSON for backend-specific notes
SQLite as of version 3.9 - see sqlalchemy.dialects.sqlite.JSON for backend-specific notes
Microsoft SQL Server 2016 and later - see sqlalchemy.dialects.mssql.JSON for backend-specific notes

JSON is part of the Core in support of the growing popularity of native JSON datatypes.

The JSON type stores arbitrary JSON format data, e.g.:

data_table = Table('data_table', metadata,
    Column('id', Integer, primary_key=True),
    Column('data', JSON)
)
with engine.connect() as conn:
    conn.execute(
        data_table.insert(),
        data = {"key1": "value1", "key2": "value2"}
    )

JSON-Specific Expression Operators

The JSON datatype provides these additional SQL operations:

Keyed index operations:
```
data_table.c.data['some key']
```
Integer index operations:
```
data_table.c.data[3]
```

Path index operations:

data_table.c.data[('key_1', 'key_2', 5, ..., 'key_n')]

Data casters for specific JSON element types, subsequent to an index or path operation being invoked:
```
data_table.c.data["some key"].as_integer()
```
New in version 1.3.11.

Additional operations may be available from the dialect-specific versions of JSON, such as sqlalchemy.dialects.postgresql.JSON and sqlalchemy.dialects.postgresql.JSONB which both offer additional PostgreSQL-specific operations.

Casting JSON Elements to Other Types

Index operations, i.e. those invoked by calling upon the expression using the Python bracket operator as in some_column['some key'], return an expression object whose type defaults to JSON by default, so that further JSON-oriented instructions may be called upon the result type. However, it is likely more common that an index operation is expected to return a specific scalar element, such as a string or integer. In order to provide access to these elements in a backend-agnostic way, a series of data casters are provided:

Comparator.as_string() - return the element as a string
Comparator.as_boolean() - return the element as a boolean
Comparator.as_float() - return the element as a float
Comparator.as_integer() - return the element as an integer

These data casters are implemented by supporting dialects in order to assure that comparisons to the above types will work as expected, such as:

# integer comparison
data_table.c.data["some_integer_key"].as_integer() == 5
# boolean comparison
data_table.c.data["some_boolean"].as_boolean() == True

New in version 1.3.11: Added type-specific casters for the basic JSON data element types.

Note

The data caster functions are new in version 1.3.11, and supersede the previous documented approaches of using CAST; for reference, this looked like:

from sqlalchemy import cast, type_coerce
from sqlalchemy import String, JSON
cast(
    data_table.c.data['some_key'], String
) == type_coerce(55, JSON)

The above case now works directly as:

data_table.c.data['some_key'].as_integer() == 5

For details on the previous comparison approach within the 1.3.x series, see the documentation for SQLAlchemy 1.2 or the included HTML files in the doc/ directory of the version’s distribution.

Detecting Changes in JSON columns when using the ORM

The JSON type, when used with the SQLAlchemy ORM, does not detect in-place mutations to the structure. In order to detect these, the sqlalchemy.ext.mutable extension must be used. This extension will allow “in-place” changes to the datastructure to produce events which will be detected by the unit of work. See the example at HSTORE for a simple example involving a dictionary.

Support for JSON null vs. SQL NULL

When working with NULL values, the JSON type recommends the use of two specific constants in order to differentiate between a column that evaluates to SQL NULL, e.g. no value, vs. the JSON-encoded string of "null". To insert or select against a value that is SQL NULL, use the constant null():

from sqlalchemy import null
conn.execute(table.insert(), json_value=null())

To insert or select against a value that is JSON "null", use the constant JSON.NULL:

conn.execute(table.insert(), json_value=JSON.NULL)

The JSON type supports a flag JSON.none_as_null which when set to True will result in the Python constant None evaluating to the value of SQL NULL, and when set to False results in the Python constant None evaluating to the value of JSON "null". The Python value None may be used in conjunction with either JSON.NULL and null() in order to indicate NULL values, but care must be taken as to the value of the JSON.none_as_null in these cases.

Customizing the JSON Serializer

The JSON serializer and deserializer used by JSON defaults to Python’s json.dumps and json.loads functions; in the case of the psycopg2 dialect, psycopg2 may be using its own custom loader function.

In order to affect the serializer / deserializer, they are currently configurable at the create_engine() level via the create_engine.json_serializer and create_engine.json_deserializer parameters. For example, to turn off ensure_ascii:

engine = create_engine(
    "sqlite://",
    json_serializer=lambda obj: json.dumps(obj, ensure_ascii=False))

Changed in version 1.3.7: SQLite dialect’s json_serializer and json_deserializer parameters renamed from _json_serializer and _json_deserializer.

See also

sqlalchemy.dialects.postgresql.JSON

sqlalchemy.dialects.postgresql.JSONB

sqlalchemy.dialects.mysql.JSON

sqlalchemy.dialects.sqlite.JSON

New in version 1.1.

Class signature

class sqlalchemy.types.JSON (sqlalchemy.types.Indexable, sqlalchemy.types.TypeEngine)

class Comparator(expr)

Define comparison operations for JSON.

Class signature

class sqlalchemy.types.JSON.Comparator (sqlalchemy.types.Comparator, sqlalchemy.types.Comparator)
- method sqlalchemy.types.JSON.Comparator.as_boolean()
  
  Cast an indexed value as boolean.
  
  e.g.:
```
stmt = select(
    mytable.c.json_column['some_data'].as_boolean()
).where(
    mytable.c.json_column['some_data'].as_boolean() == True
)
```
  New in version 1.3.11.
- method sqlalchemy.types.JSON.Comparator.as_float()
  
  Cast an indexed value as float.
  
  e.g.:
```
stmt = select(
    mytable.c.json_column['some_data'].as_float()
).where(
    mytable.c.json_column['some_data'].as_float() == 29.75
)
```
  New in version 1.3.11.
- method sqlalchemy.types.JSON.Comparator.as_integer()
  
  Cast an indexed value as integer.
  
  e.g.:
```
stmt = select(
    mytable.c.json_column['some_data'].as_integer()
).where(
    mytable.c.json_column['some_data'].as_integer() == 5
)
```
  New in version 1.3.11.
- method sqlalchemy.types.JSON.Comparator.as_json()
  
  Cast an indexed value as JSON.
  
  e.g.:
```
stmt = select(mytable.c.json_column['some_data'].as_json())
```
  This is typically the default behavior of indexed elements in any case.
  
  Note that comparison of full JSON structures may not be supported by all backends.
  
  New in version 1.3.11.
- method sqlalchemy.types.JSON.Comparator.as_numeric(precision, scale, asdecimal=True)
  
  Cast an indexed value as numeric/decimal.
  
  e.g.:
```
stmt = select(
    mytable.c.json_column['some_data'].as_numeric(10, 6)
).where(
    mytable.c.
    json_column['some_data'].as_numeric(10, 6) == 29.75
)
```
  New in version 1.4.0b2.
- method sqlalchemy.types.JSON.Comparator.as_string()
  
  Cast an indexed value as string.
  
  e.g.:
```
stmt = select(
    mytable.c.json_column['some_data'].as_string()
).where(
    mytable.c.json_column['some_data'].as_string() ==
    'some string'
)
```
  New in version 1.3.11.
class JSONElementType

Common function for index / path elements in a JSON expression.

Class signature

class sqlalchemy.types.JSON.JSONElementType (sqlalchemy.types.TypeEngine)
- method sqlalchemy.types.JSON.JSONElementType.bind_processor(dialect)
  
  Return a conversion function for processing bind values.
  
  Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.
  
  If processing is not necessary, the method should return None.
  
  Parameters
  
  dialect – Dialect instance in use.
- method sqlalchemy.types.JSON.JSONElementType.literal_processor(dialect)
  
  Return a conversion function for processing literal values that are to be rendered directly without using binds.
  
  This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.
  
  New in version 0.9.0.
- method sqlalchemy.types.JSON.JSONElementType.string_bind_processor(dialect)
- method sqlalchemy.types.JSON.JSONElementType.string_literal_processor(dialect)
class JSONIndexType

Placeholder for the datatype of a JSON index value.

This allows execution-time processing of JSON index values for special syntaxes.

Class signature

class sqlalchemy.types.JSON.JSONIndexType (sqlalchemy.types.JSONElementType)
class JSONIntIndexType

Placeholder for the datatype of a JSON index value.

This allows execution-time processing of JSON index values for special syntaxes.

Class signature

class sqlalchemy.types.JSON.JSONIntIndexType (sqlalchemy.types.JSONIndexType)
class JSONPathType

Placeholder type for JSON path operations.

This allows execution-time processing of a path-based index value into a specific SQL syntax.

Class signature

class sqlalchemy.types.JSON.JSONPathType (sqlalchemy.types.JSONElementType)
class JSONStrIndexType

Placeholder for the datatype of a JSON index value.

This allows execution-time processing of JSON index values for special syntaxes.

Class signature

class sqlalchemy.types.JSON.JSONStrIndexType (sqlalchemy.types.JSONIndexType)
attribute sqlalchemy.types.JSON.NULL = symbol(‘JSON_NULL’)

Describe the json value of NULL.

This value is used to force the JSON value of "null" to be used as the value. A value of Python None will be recognized either as SQL NULL or JSON "null", based on the setting of the JSON.none_as_null flag; the JSON.NULL constant can be used to always resolve to JSON "null" regardless of this setting. This is in contrast to the null() construct, which always resolves to SQL NULL. E.g.:
```
from sqlalchemy import null
from sqlalchemy.dialects.postgresql import JSON
# will *always* insert SQL NULL
obj1 = MyObject(json_value=null())
# will *always* insert JSON string "null"
obj2 = MyObject(json_value=JSON.NULL)
session.add_all([obj1, obj2])
session.commit()
```
In order to set JSON NULL as a default value for a column, the most transparent method is to use text():
```
Table(
    'my_table', metadata,
    Column('json_data', JSON, default=text("'null'"))
)
```
While it is possible to use JSON.NULL in this context, the JSON.NULL value will be returned as the value of the column, which in the context of the ORM or other repurposing of the default value, may not be desirable. Using a SQL expression means the value will be re-fetched from the database within the context of retrieving generated defaults.
method sqlalchemy.types.JSON.__init__(none_as_null=False)

Construct a JSON type.
- Parameters
  
  none_as_null=False –
  
  if True, persist the value None as a SQL NULL value, not the JSON encoding of null. Note that when this flag is False, the null() construct can still be used to persist a NULL value:
```
from sqlalchemy import null
conn.execute(table.insert(), data=null())
```
  Note
  
  JSON.none_as_null does not apply to the values passed to Column.default and Column.server_default; a value of None passed for these parameters means “no default present”.
  
  See also
  
  JSON.NULL
method sqlalchemy.types.JSON.bind_processor(dialect)

Return a conversion function for processing bind values.

Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

If processing is not necessary, the method should return None.
- Parameters
  
  dialect – Dialect instance in use.
attribute sqlalchemy.types.JSON.comparator_factory

alias of sqlalchemy.sql.sqltypes.JSON.Comparator
attribute sqlalchemy.types.JSON.python_type
method sqlalchemy.types.JSON.result_processor(dialect, coltype)

Return a conversion function for processing result row values.

Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

If processing is not necessary, the method should return None.
- Parameters
  - dialect – Dialect instance in use.
  - coltype – DBAPI coltype argument received in cursor.description.

attribute sqlalchemy.types.JSON.should_evaluate_none

If True, the Python constant None is considered to be handled explicitly by this type.

The ORM uses this flag to indicate that a positive value of None is passed to the column in an INSERT statement, rather than omitting the column from the INSERT statement which has the effect of firing off column-level defaults. It also allows types which have special behavior for Python None, such as a JSON type, to indicate that they’d like to handle the None value explicitly.

To set this flag on an existing type, use the TypeEngine.evaluates_none() method.

See also

TypeEngine.evaluates_none()

New in version 1.1.

class sqlalchemy.types.``INTEGER

The SQL INT or INTEGER type.

Class signature

class sqlalchemy.types.INTEGER (sqlalchemy.types.Integer)

class sqlalchemy.types.``NCHAR(length=None, \*kwargs*)

The SQL NCHAR type.

Class signature

class sqlalchemy.types.NCHAR (sqlalchemy.types.Unicode)

class sqlalchemy.types.``NVARCHAR(length=None, \*kwargs*)

The SQL NVARCHAR type.

Class signature

class sqlalchemy.types.NVARCHAR (sqlalchemy.types.Unicode)

class sqlalchemy.types.``NUMERIC(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

The SQL NUMERIC type.

Class signature

class sqlalchemy.types.NUMERIC (sqlalchemy.types.Numeric)

class sqlalchemy.types.``REAL(precision=None, asdecimal=False, decimal_return_scale=None)

The SQL REAL type.

Class signature

class sqlalchemy.types.REAL (sqlalchemy.types.Float)

class sqlalchemy.types.``SMALLINT

The SQL SMALLINT type.

Class signature

class sqlalchemy.types.SMALLINT (sqlalchemy.types.SmallInteger)

class sqlalchemy.types.``TEXT(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

The SQL TEXT type.

Class signature

class sqlalchemy.types.TEXT (sqlalchemy.types.Text)

class sqlalchemy.types.``TIME(timezone=False)

The SQL TIME type.

Class signature

class sqlalchemy.types.TIME (sqlalchemy.types.Time)

class sqlalchemy.types.``TIMESTAMP(timezone=False)

The SQL TIMESTAMP type.

TIMESTAMP datatypes have support for timezone storage on some backends, such as PostgreSQL and Oracle. Use the TIMESTAMP.timezone argument in order to enable “TIMESTAMP WITH TIMEZONE” for these backends.

Class signature

class sqlalchemy.types.TIMESTAMP (sqlalchemy.types.DateTime)

method sqlalchemy.types.TIMESTAMP.__init__(timezone=False)

Construct a new TIMESTAMP.
- Parameters
  
  timezone – boolean. Indicates that the TIMESTAMP type should enable timezone support, if available on the target database. On a per-dialect basis is similar to “TIMESTAMP WITH TIMEZONE”. If the target database does not support timezones, this flag is ignored.
method sqlalchemy.types.TIMESTAMP.get_dbapi_type(dbapi)

Return the corresponding type object from the underlying DB-API, if any.

This can be useful for calling setinputsizes(), for example.

class sqlalchemy.types.``VARBINARY(length=None)

The SQL VARBINARY type.

Class signature

class sqlalchemy.types.VARBINARY (sqlalchemy.types._Binary)

class sqlalchemy.types.``VARCHAR(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

The SQL VARCHAR type.

Class signature

class sqlalchemy.types.VARCHAR (sqlalchemy.types.String)

Vendor-Specific Types

Database-specific types are also available for import from each database’s dialect module. See the Dialects reference for the database you’re interested in.

For example, MySQL has a BIGINT type and PostgreSQL has an INET type. To use these, import them from the module explicitly:

from sqlalchemy.dialects import mysql
table = Table('foo', metadata,
    Column('id', mysql.BIGINT),
    Column('enumerates', mysql.ENUM('a', 'b', 'c'))
)

Or some PostgreSQL types:

from sqlalchemy.dialects import postgresql
table = Table('foo', metadata,
    Column('ipaddress', postgresql.INET),
    Column('elements', postgresql.ARRAY(String))
)

Each dialect provides the full set of typenames supported by that backend within its __all__ collection, so that a simple import * or similar will import all supported types as implemented for that backend:

from sqlalchemy.dialects.postgresql import *
t = Table('mytable', metadata,
           Column('id', INTEGER, primary_key=True),
           Column('name', VARCHAR(300)),
           Column('inetaddr', INET)
)

Where above, the INTEGER and VARCHAR types are ultimately from sqlalchemy.types, and INET is specific to the PostgreSQL dialect.

Some dialect level types have the same name as the SQL standard type, but also provide additional arguments. For example, MySQL implements the full range of character and string types including additional arguments such as collation and charset:

from sqlalchemy.dialects.mysql import VARCHAR, TEXT
table = Table('foo', meta,
    Column('col1', VARCHAR(200, collation='binary')),
    Column('col2', TEXT(charset='latin1'))
)