Dapper Tutorial Dapper - QuerySingleOrDefault

Description

QuerySingleOrDefault method is an extension method that can be called from any object of type IDbConnection. It can execute a query and map the first result, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence.

The result can be mapped to:

• Anonymous
• Strongly Typed

Parameters

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

First, Single & Default

Be careful to use the right method. First & Single methods are very different.

Example - Query Anonymous

Execute a query and map the first result to a dynamic list, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence.

string sql = "SELECT * FROM OrderDetails WHERE OrderDetailID = @OrderDetailID;";

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{
    var orderDetail = connection.QuerySingleOrDefault(sql, new {OrderDetailID = 1});

    FiddleHelper.WriteTable(orderDetail);
}

Try it: .NET Core | .NET Framework

Example - Query Strongly Typed

Execute a query and map the first result to a strongly typed list, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence.

string sql = "SELECT * FROM OrderDetails WHERE OrderDetailID = @OrderDetailID;";

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDetail = connection.QuerySingleOrDefault<OrderDetail>(sql, new {OrderDetailID = 1});

    FiddleHelper.WriteTable(new List<OrderDetail>() { orderDetail });
}

Try it: .NET Core | .NET Framework