Quarkus - Reactive SQL Clients

The Reactive SQL Clients have a straightforward API focusing on scalability and low-overhead. Currently, the following database servers are supported:

• DB2

• PostgreSQL

• MariaDB/MySQL

In this guide, you will learn how to implement a simple CRUD application exposing data stored in PostgreSQL over a RESTful API.

The application shall manage fruit entities:

public class Fruit {
    public Long id;
    public String name;
    public Fruit() {
    }
    public Fruit(String name) {
        this.name = name;
    }
    public Fruit(Long id, String name) {
        this.id = id;
        this.name = name;
    }
}

docker run —ulimit memlock=-1:-1 -it —rm=true —memory-swappiness=0 —name quarkus_test -e POSTGRES_USER=quarkus_test -e POSTGRES_PASSWORD=quarkus_test -e POSTGRES_DB=quarkus_test -p 5432:5432 postgres:10.5

Installing

Reactive PostgreSQL Client extension

First, make sure your project has the quarkus-reactive-pg-client extension enabled. If you are creating a new project, set the extensions parameter as follows:

mvn io.quarkus:quarkus-maven-plugin:1.7.6.Final:create \
    -DprojectGroupId=org.acme \
    -DprojectArtifactId=reactive-pg-client-quickstart \
    -Dextensions="reactive-pg-client"
cd reactive-pg-client-quickstart

If you have an already created project, the reactive-pg-client extension can be added to an existing Quarkus project with the add-extension command:

./mvnw quarkus:add-extension -Dextensions="reactive-pg-client"

Otherwise, you can manually add this to the dependencies section of your pom.xml file:

<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-reactive-pg-client</artifactId>
</dependency>

Mutiny

Reactive REST endpoints in your application that return Uni or Multi need Mutiny support for RESTEasy extension (io.quarkus:quarkus-resteasy-mutiny) to work properly:

./mvnw quarkus:add-extension -Dextensions="resteasy-mutiny"

JSON Binding

We will expose Fruit instances over HTTP in the JSON format. Consequently, you also need to add the quarkus-resteasy-jsonb extension:

./mvnw quarkus:add-extension -Dextensions="resteasy-jsonb"

If you prefer not to use the command line, manually add this to the dependencies section of your pom.xml file:

<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-resteasy-jsonb</artifactId>
</dependency>

Of course, this is only a requirement for this guide, not any application using the Reactive PostgreSQL Client.

Configuring

The Reactive PostgreSQL Client can be configured with standard Quarkus datasource properties and a reactive URL:

src/main/resources/application.properties

quarkus.datasource.db-kind=postgresql
quarkus.datasource.username=quarkus_test
quarkus.datasource.password=quarkus_test
quarkus.datasource.reactive.url=postgresql://localhost:5432/quarkus_test

With that you may create your FruitResource skeleton and @Inject a io.vertx.mutiny.pgclient.PgPool instance:

src/main/java/org/acme/vertx/FruitResource.java

@Path("fruits")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class FruitResource {
    @Inject
    io.vertx.mutiny.pgclient.PgPool client;
}

Database schema and seed data

Before we implement the REST endpoint and data management code, we need to setup the database schema. It would also be convenient to have some data inserted upfront.

For production we would recommend to use something like the Flyway database migration tool. But for development we can simply drop and create the tables on startup, and then insert a few fruits.

src/main/java/org/acme/vertx/FruitResource.java

@Inject
@ConfigProperty(name = "myapp.schema.create", defaultValue = "true") (1)
boolean schemaCreate;
@PostConstruct
void config() {
    if (schemaCreate) {
        initdb();
    }
}
private void initdb() {
    // TODO
}

Almost ready! To initialize the DB in development mode, we will use the client simple query method. It returns a Uni and thus can be composed to execute queries sequentially:

client.query("DROP TABLE IF EXISTS fruits").execute()
    .flatMap(r -> client.query("CREATE TABLE fruits (id SERIAL PRIMARY KEY, name TEXT NOT NULL)").execute())
    .flatMap(r -> client.query("INSERT INTO fruits (name) VALUES ('Orange')").execute())
    .flatMap(r -> client.query("INSERT INTO fruits (name) VALUES ('Pear')").execute())
    .flatMap(r -> client.query("INSERT INTO fruits (name) VALUES ('Apple')").execute())
    .await().indefinitely();

That’s it! So far we have seen how to configure a pooled client and execute simple queries. We are now ready to develop the data management code and implement our RESTful endpoint.

Using

Query results traversal

In development mode, the database is set up with a few rows in the fruits table. To retrieve all the data, we will use the query method again:

Uni<RowSet<Row>> rowSet = client.query("SELECT id, name FROM fruits ORDER BY name ASC").execute();

When the operation completes, we will get a RowSet that has all the rows buffered in memory. A RowSet is an java.lang.Iterable<Row> and thus can be converted to a Multi:

Multi<Fruit> fruits = rowSet
  .onItem().transformToMulti(set -> Multi.createFrom().iterable(set))
  .onItem().transform(Fruit::from);

The Fruit#from method converts a Row instance to a Fruit instance. It is extracted as a convenience for the implementation of the other data management methods:

src/main/java/org/acme/vertx/Fruit.java

private static Fruit from(Row row) {
    return new Fruit(row.getLong("id"), row.getString("name"));
}

Putting it all together, the Fruit.findAll method looks like:

src/main/java/org/acme/vertx/Fruit.java

public static Multi<Fruit> findAll(PgPool client) {
    return client.query("SELECT id, name FROM fruits ORDER BY name ASC").execute()
            .onItem().transformToMulti(set -> Multi.createFrom().iterable(set))
            .onItem().transform(Fruit::from);
}

And the endpoint to get all fruits from the backend:

src/main/java/org/acme/vertx/FruitResource.java

@GET
public Multi<Fruit> get() {
    return Fruit.findAll(client);
}

Now start Quarkus in dev mode with:

./mvnw compile quarkus:dev

Lastly, open your browser and navigate to http://localhost:8080/fruits, you should see:

[{"id":3,"name":"Apple"},{"id":1,"name":"Orange"},{"id":2,"name":"Pear"}]

Prepared queries

The Reactive PostgreSQL Client can also prepare queries and take parameters that are replaced in the SQL statement at execution time:

client.preparedQuery("SELECT id, name FROM fruits WHERE id = $1").execute(Tuple.of(id))

Similar to the simple query method, preparedQuery returns an instance of PreparedQuery<RowSet<Row>>. Equipped with this tooling, we are able to safely use an id provided by the user to get the details of a particular fruit:

src/main/java/org/acme/vertx/Fruit.java

public static Uni<Fruit> findById(PgPool client, Long id) {
    return client.preparedQuery("SELECT id, name FROM fruits WHERE id = $1").execute(Tuple.of(id)) (1)
            .onItem().transform(RowSet::iterator) (2)
            .onItem().transform(iterator -> iterator.hasNext() ? from(iterator.next()) : null); (3)
}

And in the JAX-RS resource:

src/main/java/org/acme/vertx/FruitResource.java

@GET
@Path("{id}")
public Uni<Response> getSingle(@PathParam Long id) {
    return Fruit.findById(client, id)
            .onItem().transform(fruit -> fruit != null ? Response.ok(fruit) : Response.status(Status.NOT_FOUND)) (1)
            .onItem().transform(ResponseBuilder::build); (2)
}

The same logic applies when saving a Fruit:

src/main/java/org/acme/vertx/Fruit.java

public Uni<Long> save(PgPool client) {
    return client.preparedQuery("INSERT INTO fruits (name) VALUES ($1) RETURNING (id)").execute(Tuple.of(name))
            .onItem().transform(pgRowSet -> pgRowSet.iterator().next().getLong("id"));
}

And in the web resource we handle the POST request:

src/main/java/org/acme/vertx/FruitResource.java

@POST
public Uni<Response> create(Fruit fruit) {
    return fruit.save(client)
            .onItem().transform(id -> URI.create("/fruits/" + id))
            .onItem().transform(uri -> Response.created(uri).build());
}

Result metadata

A RowSet does not only hold your data in memory, it also gives you some information about the data itself, such as:

• the number of rows affected by the query (inserted/deleted/updated/retrieved depending on the query type),

• the column names.

Let’s use this to support removal of fruits in the database:

src/main/java/org/acme/vertx/Fruit.java

public static Uni<Boolean> delete(PgPool client, Long id) {
    return client.preparedQuery("DELETE FROM fruits WHERE id = $1").execute(Tuple.of(id))
            .onItem().transform(pgRowSet -> pgRowSet.rowCount() == 1); (1)
}

And to handle the HTTP DELETE method in the web resource:

src/main/java/org/acme/vertx/FruitResource.java

@DELETE
@Path("{id}")
public Uni<Response> delete(@PathParam Long id) {
    return Fruit.delete(client, id)
            .onItem().transform(deleted -> deleted ? Status.NO_CONTENT : Status.NOT_FOUND)
            .onItem().transform(status -> Response.status(status).build());
}

With GET, POST and DELETE methods implemented, we may now create a minimal web page to try the RESTful application out. We will use jQuery to simplify interactions with the backend:

<!doctype html>
<html>
<head>
    <meta charset="utf-8"/>
    <title>Reactive PostgreSQL Client - Quarkus</title>
    <script src="https://code.jquery.com/jquery-3.3.1.min.js"
            integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script>
    <script type="application/javascript" src="fruits.js"></script>
</head>
<body>
<h1>Fruits API Testing</h1>
<h2>All fruits</h2>
<div id="all-fruits"></div>
<h2>Create Fruit</h2>
<input id="fruit-name" type="text">
<button id="create-fruit-button" type="button">Create</button>
<div id="create-fruit"></div>
</body>
</html>

In the Javascript code, we need a function to refresh the list of fruits when:

• the page is loaded, or

• a fruit is added, or

• a fruit is deleted.

function refresh() {
    $.get('/fruits', function (fruits) {
        var list = '';
        (fruits || []).forEach(function (fruit) { (1)
            list = list
                + '<tr>'
                + '<td>' + fruit.id + '</td>'
                + '<td>' + fruit.name + '</td>'
                + '<td><a href="#" onclick="deleteFruit(' + fruit.id + ')">Delete</a></td>'
                + '</tr>'
        });
        if (list.length > 0) {
            list = ''
                + '<table><thead><th>Id</th><th>Name</th><th></th></thead>'
                + list
                + '</table>';
        } else {
            list = "No fruits in database"
        }
        $('#all-fruits').html(list);
    });
}
function deleteFruit(id) {
    $.ajax('/fruits/' + id, {method: 'DELETE'}).then(refresh);
}
$(document).ready(function () {
    $('#create-fruit-button').click(function () {
        var fruitName = $('#fruit-name').val();
        $.post({
            url: '/fruits',
            contentType: 'application/json',
            data: JSON.stringify({name: fruitName})
        }).then(refresh);
    });
    refresh();
});

All done! Navigate to http://localhost:8080/fruits.html and read/create/delete some fruits.

Database Clients details

Transactions

The reactive SQL clients support transactions. A transaction is started with client.begin() and terminated with either tx.commit() or tx.rollback(). All these operations are asynchronous:

• client.begin() returns a Uni<Transaction>

• client.commit() and client.rollback() return Uni<Void>

Managing transactions in the reactive programming world can be cumbersome. Instead of writing repetitive and complex (thus error-prone!) code, you can use the io.vertx.mutiny.sqlclient.SqlClientHelper.

The following snippet shows how to run 2 insertions in the same transaction:

public static Uni<Void> insertTwoFruits(PgPool client, Fruit fruit1, Fruit fruit2) {
    return SqlClientHelper.inTransactionUni(client, tx -> {
        Uni<RowSet<Row>> insertOne = tx.preparedQuery("INSERT INTO fruits (name) VALUES ($1) RETURNING (id)")
                .execute(Tuple.of(fruit1.name));
        Uni<RowSet<Row>> insertTwo = tx.preparedQuery("INSERT INTO fruits (name) VALUES ($1) RETURNING (id)")
                .execute(Tuple.of(fruit2.name));
        return insertOne.and(insertTwo)
                // Ignore the results (the two ids)
                .onItem().ignore().andContinueWithNull();
    });
}

In this example, the transaction is automatically committed on success or rolled back on failure.

You can also create dependent actions as follows:

return SqlClientHelper.inTransactionUni(client, tx -> tx
        .preparedQuery("INSERT INTO person (firstname,lastname) VALUES ($1,$2) RETURNING (id)")
                .execute(Tuple.of(person.getFirstName(), person.getLastName()))
        .onItem().transformToUni(id -> tx.preparedQuery("INSERT INTO addr (person_id,addrline1) VALUES ($1,$2)")
                .execute(Tuple.of(id.iterator().next().getLong("id"), person.getLastName())))
        .onItem().ignore().andContinueWithNull());

UNIX Domain Socket connections

The PostgreSQL and MariaDB/MySQL clients can be configured to connect to the server through a UNIX domain socket.

First make sure that native transport support is enabled.

Then configure the database connection url. This step depends on the database type.

PostgreSQL

PostgresSQL domain socket paths have the following form: <directory>/.s.PGSQL.<port>

The database connection url must be configured so that:

• the host is the directory in the socket path

• the port is the port in the socket path

Consider the following socket path: /var/run/postgresql/.s.PGSQL.5432.

In application.properties add:

quarkus.datasource.reactive.url=postgresql://:5432/quarkus_test?host=/var/run/postgresql

MariaDB/MySQL

The database connection url must be configured so that the host is the socket path.

Consider the following socket path: /var/run/mysqld/mysqld.sock.

In application.properties add:

quarkus.datasource.reactive.url=mysql:///quarkus_test?host=/var/run/mysqld/mysqld.sock

Configuration Reference

Common Datasource

Reactive Datasource

DB2

MariaDB/MySQL

PostgreSQL