Dapper - Query

Description

Query method is an extension method which 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 different parameter of an Query method.

Name	Description
sql	The query to execute.
param	The query parameters (default = null).
transaction	The transaction to use (default = null).
buffered	True to buffer readeing the results of the query (default = true).
commandTimeout	The command timeout (default = null)
commandType	The command type (default = null)

Example - Query Anonymous

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

string sql = "SELECT TOP 10 * FROM OrderDetails";

using (var connection = new SqlCeConnection("Data Source=SqlCe_W3Schools.sdf"))
{	
	var orderDetail = connection.Query(sql).FirstOrDefault();

	FiddleHelper.WriteTable(orderDetail);
}

Try it online

Example - Query Strongly Typed

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

string sql = "SELECT TOP 10 * FROM OrderDetails";

using (var connection = new SqlCeConnection("Data Source=SqlCe_W3Schools.sdf"))
{			
	var orderDetails = connection.Query<OrderDetail>(sql).ToList();

	Console.WriteLine(orderDetails.Count);

	FiddleHelper.WriteTable(orderDetails);
}

Try it online

Example - Query Multi-Mapping (One to One)

Raw SQL query can be executed using 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)

Raw SQL query can be executed using Query method and map the result to a strongly typed list with a 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 SqlCeConnection("Data Source=SqlCe_W3Schools.sdf"))
{			
	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 online

Example - Query Multi-Type

Raw SQL query can be executed using 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);
}