Querying Multiple Results With Dapper

You can execute multiple queries in a single SQL statement using the QueryMultiple method (if the database provider supports it). Once executed, you can map the returned results to multiple objects using methods such as Read<T>, ReadFirst<T>, ReadSingle<T> and more.

The Dapper QueryMultiple method allows you to select multiple results from a database query. That feature is very useful for selecting multiple results sets at once, thus avoiding unnecessary round trips to the database server.

• The QueryMultiple method provides a simple way of fetching data stored in different tables or views with a single database query.
• By using dapper's QueryMultiple method, you can select multiple rows from different tables in one go, saving time and resources.
• Dapper's QueryMultiple method allows you to map results from multiple queries into strongly typed collections that can be easily consumed within your application code.
• Using Dapper QueryMultiple is an efficient way to select multiple results from a single database query.
• It saves time and resources by avoiding unnecessary round trips to the database server and eliminates the need for complex SQL queries.

After using the QueryMultiple or QueryMultipleAsync method, you can use the following methods with the results:

Dapper QueryMultiple

The following example demonstrates how to use Dapper QueryMultiple to execute multiple SQL statements in one query.

string sql = @"
SELECT * FROM [Order] WHERE OrderID = @orderID;
SELECT * FROM [OrderItem] WHERE OrderID = @orderID;
";

using (var multi = connection.QueryMultiple(sql, new {orderID = 1}))
{
   var order = multi.ReadFirst<Order>();
   var orderItems = multi.Read<OrderItem>().ToList();
 
   FiddleHelper.WriteTable("Order", new List<Order>() { order});
   FiddleHelper.WriteTable("OrderItem", orderItems);
}

Online Example

With this, we can execute multiple SQL statements in one query and read each result set from the GridReader object returned by the QueryMultiple method. That can help increase the performance of your application in cases where multiple queries need to be executed and their results combined.

Using Dapper QueryMultiple is a great way to simplify data access and ensure that your application runs quickly and efficiently. With its easy-to-use API, you can quickly set up complex queries and access the data you need.

Dapper QueryMultipleAsync

The asynchronous version of the QueryMultiple<T> method is QueryMultipleAsync<T>:

var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServer());

string sql = @"
SELECT * FROM [Order] WHERE OrderID = @orderID;
SELECT * FROM [OrderItem] WHERE OrderID = @orderID;
";

using (var multi = await connection.QueryMultipleAsync(sql, new {orderID = 1}))
{
   var order = multi.ReadFirst<Order>();
   var orderItems = multi.Read<OrderItem>().ToList();
 
   FiddleHelper.WriteTable("Order", new List<Order>() { order});
   FiddleHelper.WriteTable("OrderItem", orderItems);
}

Online Example

Related Articles

• Querying
• Stored Procedure
• Using Parameters
• Buffered & Unbuffered Queries