Dapper Tutorial Dapper - Query Method
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:
Parameters
The following table shows the different parameters of a 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 reading the results of the query (default = true). |
| commandTimeout | The command timeout (default = null) |
| commandType | The command type (default = null) |
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); }