Dapper - QuerySingle

Dapper - QuerySingle

Description

QuerySingle 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 and throws an exception if there is not exactly one element in the sequence.

The result can be mapped to:

Anonymous
Strongly Typed

Parameters

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

Name	Description
sql	The query to execute.
param	The query parameters (default = null).
transaction	The transaction to use (default = null).
commandTimeout	The command timeout (default = null)
commandType	The command type (default = null)

First, Single & Default

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

Result	No Item	One Item	Many Items
First	Exception	Item	First Item
Single	Exception	Item	Exception
FirstOrDefault	Default	Item	First Item
SingleOrDefault	Default	Item	Exception

Example - Query Anonymous

Execute a query and map the first result to a dynamic list, and throws an exception if there is not exactly one element in the sequence.

string sql = "SELECT * FROM OrderDetails WHERE OrderDetailID = @OrderDetailID;";
using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{    
    var orderDetail = connection.QuerySingle(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, and throws an exception if there is not exactly one element in the sequence.

string sql = "SELECT * FROM OrderDetails WHERE OrderDetailID = @OrderDetailID;";
using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDetail = connection.QuerySingle<OrderDetail>(sql, new {OrderDetailID = 1});
    FiddleHelper.WriteTable(new List<OrderDetail>() { orderDetail });
}

Try it: .NET Core | .NET Framework