Dapper - Query

Description

Query method is an extension method that can be called from any object of type IDbConnection. It can execute a query and map the result.

The result can be mapped to:

• Anonymous
• Strongly Typed
• Multi-Mapping (One to One)
• Multi-Mapping (One to Many)
• Multi-Type

Parameters

The following table shows the different parameters of a Query method.

Example - Query Anonymous

The raw SQL query can be executed using the Query method and map the result to a dynamic list.

string sql = "SELECT TOP 10 * FROM OrderDetails";
using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{    
    var orderDetail = connection.Query(sql).FirstOrDefault();
    FiddleHelper.WriteTable(orderDetail);
}

Try it: .NET Core | .NET Framework

Example - Query Strongly Typed

The raw SQL query can be executed using the Query method and map the result to a strongly typed list.

string sql = "SELECT TOP 10 * FROM OrderDetails";
using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDetails = connection.Query<OrderDetail>(sql).ToList();
    Console.WriteLine(orderDetails.Count);
    FiddleHelper.WriteTable(orderDetails);
}

Try it: .NET Core | .NET Framework

Example - Query Multi-Mapping (One to One)

The raw SQL query can be executed using the Query method and map the result to a strongly typed list with a one to one relation.

string sql = "SELECT * FROM Invoice AS A INNER JOIN InvoiceDetail AS B ON A.InvoiceID = B.InvoiceID;";
using (var connection = My.ConnectionFactory())
{
    connection.Open();
    var invoices = connection.Query<Invoice, InvoiceDetail, Invoice>(
            sql,
            (invoice, invoiceDetail) =>
            {
                invoice.InvoiceDetail = invoiceDetail;
                return invoice;
            },
            splitOn: "InvoiceID")
        .Distinct()
        .ToList();
}

Example - Query Multi-Mapping (One to Many)

The raw SQL query can be executed using the Query method and map the result to a strongly typed list with one-to-many relations.

string sql = "SELECT TOP 10 * FROM Orders AS A INNER JOIN OrderDetails AS B ON A.OrderID = B.OrderID;";
using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDictionary = new Dictionary<int, Order>();
    var list = connection.Query<Order, OrderDetail, Order>(
    sql,
    (order, orderDetail) =>
    {
        Order orderEntry;
        if (!orderDictionary.TryGetValue(order.OrderID, out orderEntry))
        {
        orderEntry = order;
        orderEntry.OrderDetails = new List<OrderDetail>();
        orderDictionary.Add(orderEntry.OrderID, orderEntry);
        }
        orderEntry.OrderDetails.Add(orderDetail);
        return orderEntry;
    },
    splitOn: "OrderID")
    .Distinct()
    .ToList();
    Console.WriteLine(list.Count);
    FiddleHelper.WriteTable(list);
    FiddleHelper.WriteTable(list.First().OrderDetails);
}

Try it: .NET Core | .NET Framework

Example - Query Multi-Type

The raw SQL query can be executed using the Query method and map the result to a list of different types.

string sql = "SELECT * FROM Invoice;";
using (var connection = My.ConnectionFactory())
{
    connection.Open();
    var invoices = new List<Invoice>();
    using (var reader = connection.ExecuteReader(sql))
    {
        var storeInvoiceParser = reader.GetRowParser<StoreInvoice>();
        var webInvoiceParser = reader.GetRowParser<WebInvoice>();
        while (reader.Read())
        {
            Invoice invoice;
            switch ((InvoiceKind) reader.GetInt32(reader.GetOrdinal("Kind")))
            {
                case InvoiceKind.StoreInvoice:
                    invoice = storeInvoiceParser(reader);
                    break;
                case InvoiceKind.WebInvoice:
                    invoice = webInvoiceParser(reader);
                    break;
                default:
                    throw new Exception(ExceptionMessage.GeneralException);
            }
            invoices.Add(invoice);
        }
    }
    My.Result.Show(invoices);
}