結(jié)果強(qiáng)類型

描述

可以使用擴(kuò)展方法執(zhí)行查詢并使用動(dòng)態(tài)類型映射結(jié)果。

強(qiáng)類型結(jié)果可以從以下擴(kuò)展方法映射：

• Query
• QueryFirst
• QueryFirstOrDefault
• QuerySingle
• QuerySingleOrDefault

這些擴(kuò)展方法可以從IDbConnection類型的任意對(duì)象中調(diào)用。

案例 - Query

Query方法可以執(zhí)行查詢并將結(jié)果映射到強(qiáng)類型列表。

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);
}

案例 - QueryFirst

QueryFirst方法可以執(zhí)行查詢并將第一個(gè)結(jié)果映射到強(qiáng)類型列表。

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

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDetail = connection.QueryFirst<OrderDetail>(sql, new {OrderDetailID = 1});

    FiddleHelper.WriteTable( new List<OrderDetail>() { orderDetail });
}

案例 - QueryFirstOrDefault

QueryFirstOrDefault方法可以執(zhí)行查詢并將第一個(gè)結(jié)果映射到強(qiáng)類型列表，如果序列不包含任何元素則為默認(rèn)值。

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

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{
    var orderDetail = connection.QueryFirstOrDefault<OrderDetail>(sql, new {OrderDetailID = 1});

    FiddleHelper.WriteTable(new List<OrderDetail>() { orderDetail });
}

案例 - QuerySingle

QuerySingle方法可以執(zhí)行查詢并將第一個(gè)結(jié)果映射到強(qiáng)類型列表，如果序列中沒有元素則會(huì)引發(fā)異常。

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

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDetail = connection.QuerySingle<OrderDetail>(sql, new {OrderDetailID = 1});

    FiddleHelper.WriteTable(new List<OrderDetail>() { orderDetail });
}

案例 - QuerySingleOrDefault

QuerySingleOrDefault方法可以執(zhí)行查詢并將第一個(gè)結(jié)果映射到強(qiáng)類型列表，如果序列為空則為默認(rèn)值；如果序列中有多個(gè)元素，則此方法將引發(fā)異常。

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

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{            
    var orderDetail = connection.QuerySingleOrDefault<OrderDetail>(sql, new {OrderDetailID = 1});

    FiddleHelper.WriteTable(new List<OrderDetail>() { orderDetail });
}