Dapper官方教程翻译10：Dapper方法之结果集类型

1.匿名结果集

 

匿名结果集支持以下方法：

• Query
• QueryFirst
• QueryFirstOrDefault
• QuerySingle
• QuerySingleOrDefault

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

using (var connection = new SqlCeConnection("Data Source=SqlCe_W3Schools.sdf"))
{			
	var orderDetails = connection.QueryFirstOrDefault(sql);

	FiddleHelper.WriteTable(orderDetails);
}

 

2.强类型结果集

 

支持以下方法：

• Query
• QueryFirst
• QueryFirstOrDefault
• QuerySingle
• QuerySingleOrDefault

 

string sql = "SELECT * FROM OrderDetails WHERE OrderDetailID = @OrderDetailID;";

using (var connection = new SqlCeConnection("Data Source=SqlCe_W3Schools.sdf"))
{
	var orderDetail = connection.QueryFirstOrDefault(sql, new {OrderDetailID = 1});

	FiddleHelper.WriteTable(new List() { orderDetail });
}

 

3.多映射

 

映射关系包括一对一及一对多：

• One to One
• One to Many

 

一对一：

 

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(
            sql,
            (invoice, invoiceDetail) =>
            {
                invoice.InvoiceDetail = invoiceDetail;
                return invoice;
            },
            splitOn: "InvoiceID")
        .Distinct()
        .ToList();
}

一对多：

 

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();


    var list = connection.Query(
        sql,
        (order, orderDetail) =>
        {
            Order orderEntry;

            if (!orderDictionary.TryGetValue(order.OrderID, out orderEntry))
            {
                orderEntry = order;
                orderEntry.OrderDetails = new List();
                orderDictionary.Add(orderEntry.OrderID, orderEntry);
            }

            orderEntry.OrderDetails.Add(orderDetail);
            return orderEntry;
        },
        splitOn: "OrderDetailID")
    .Distinct()
    .ToList();

    Console.WriteLine("Orders Count:" + list.Count);

    FiddleHelper.WriteTable(list);
    FiddleHelper.WriteTable(list.First().OrderDetails);
}

 

4.多结果集

多条查询一起执行

string sql = "SELECT * FROM Invoice WHERE InvoiceID = @InvoiceID; SELECT * FROM InvoiceItem WHERE InvoiceID = @InvoiceID;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    using (var multi = connection.QueryMultiple(sql, new {InvoiceID = 1}))
    {
        var invoice = multi.Read().First();
        var invoiceItems = multi.Read().ToList();
    }
}

 

5.多类型

结果集中并非相同的类型

string sql = "SELECT * FROM Invoice;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var invoices = new List();

    using (var reader = connection.ExecuteReader(sql))
    {
        var storeInvoiceParser = reader.GetRowParser();
        var webInvoiceParser = reader.GetRowParser();

        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);
        }
    }
}