Dapper official translation Tutorial 3: Query Dapper method of (turn)

Dapper official translation Tutorial 3: Query Dapper method of

December 20, 2018 16:51:44  Day_and_Night_2017  Reads: 271

 

Query method described

 

Query method is an extension method, it can be called IDbConnection object, you can execute a query, and mapped to the result.

You can be mapped type:

• Anonymous (anonymous type var)
• Strongly Typed (strongly typed)
• Multi-Mapping (One to One) (one to one mapping)
• Multi-Mapping (One to Many) (many maps)
• The Type-the Multi (multi-type)

 

The method can be used in Query

 

Query method Parameter Description

parameter name	Parameter Description
sql	Database statement
param	Query parameters
transaction	Services used
buffered	Whether to cache
commandTimeout	Execution timeout
commandType	Statement Types

 

Example: Query execution anonymous type

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

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

FiddleHelper.WriteTable(orderDetail);
}

Example: Query to perform strongly typed queries

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);
}

Example: one to one relationship query execution

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 execution to-many relationship

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);
}

Example: Query perform multiple 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);
}