EF中多表聯結查詢只實現了inner join並沒有實現left join，但是在實際的業務中需要用到left join的情況是很常見的。那麼我們可以通過設定左表之外的表查詢無記錄時返回預設值即可。具體參見以下程式碼。

EF程式碼：

var order = (from a in context.Set<SonOrder>()
						 join bus in context.Set<BusinessUser>() on a.BusinessID equals bus.ID 
						 join c in context.Set<LogisticsInfo>() on a.LogisticsID equals c.LogisticsID into t from c in t.DefaultIfEmpty()
						 where a.SonOrderShow == Id
						 select new OrderDetailDTO()
						{
							Address = a.FatherOrder.ReceiveAddress,	//收穫地址
							Name = a.FatherOrder.Name,	//收貨人姓名
							Phone = a.FatherOrder.Phone,	//收貨人電話
							OrderNum = a.SonOrderShow,	//訂單號
							OrderStatus = (EnumOrderStatus)a.Status,	//訂單狀態
							BusinessName = bus.BussessName,		//商家名

							InsertTime = a.FatherOrder.CreateTime,	//訂單提交時間
							PayTime = a.PayTime,	//支付時間
							SentTime = a.SendTime,	//發貨時間
							ReceiveTime = a.ReceiveTime,	//收貨時間
							CancelTime = a.CancelTime,	//取消訂單時間
							LogisticsTypeID = c.LogisticsTypeID.ToString(),	//物流型別編號
							Province = c.Province,	//省份
							City = c.City,	//城市
							Area = c.Area,	//區
							LogisticsAddress = c.LogisticsAddress,	//物流地址
							Logistics = c.Logistics,	//
							LogisticsCode = c.LogisticsCode		//物流單號

						}).FirstOrDefault();
 

生成的SQL語句如下

exec sp_executesql N'SELECT 
    [Limit1].[BusinessID] AS [BusinessID], 
    [Limit1].[ReceiveAddress] AS [ReceiveAddress], 
    [Limit1].[Name] AS [Name], 
    [Limit1].[Phone] AS [Phone], 
    [Limit1].[SonOrderShow] AS [SonOrderShow], 
    [Limit1].[Status] AS [Status], 
    [Limit1].[BussessName] AS [BussessName], 
    [Limit1].[CreateTime] AS [CreateTime], 
    [Limit1].[PayTime] AS [PayTime], 
    [Limit1].[SendTime] AS [SendTime], 
    [Limit1].[ReceiveTime] AS [ReceiveTime], 
    [Limit1].[CancelTime] AS [CancelTime], 
    [Limit1].[C1] AS [C1], 
    [Limit1].[Province] AS [Province], 
    [Limit1].[City] AS [City], 
    [Limit1].[Area] AS [Area], 
    [Limit1].[LogisticsAddress] AS [LogisticsAddress], 
    [Limit1].[Logistics] AS [Logistics], 
    [Limit1].[LogisticsCode] AS [LogisticsCode]
    FROM ( SELECT TOP (1) 
        [Extent1].[BusinessID] AS [BusinessID], 
        [Extent1].[SonOrderShow] AS [SonOrderShow], 
        [Extent1].[Status] AS [Status], 
        [Extent1].[PayTime] AS [PayTime], 
        [Extent1].[SendTime] AS [SendTime], 
        [Extent1].[ReceiveTime] AS [ReceiveTime], 
        [Extent1].[CancelTime] AS [CancelTime], 
        [Extent2].[BussessName] AS [BussessName], 
        [Extent4].[CreateTime] AS [CreateTime], 
        [Extent4].[ReceiveAddress] AS [ReceiveAddress], 
        [Extent4].[Phone] AS [Phone], 
        [Extent4].[Name] AS [Name], 
        CASE WHEN ([Extent3].[LogisticsTypeID] IS NULL) THEN N'''' ELSE  CAST( [Extent3].[LogisticsTypeID] AS nvarchar(max)) END AS [C1], 
        [Extent3].[Province] AS [Province], 
        [Extent3].[City] AS [City], 
        [Extent3].[Area] AS [Area], 
        [Extent3].[LogisticsAddress] AS [LogisticsAddress], 
        [Extent3].[Logistics] AS [Logistics], 
        [Extent3].[LogisticsCode] AS [LogisticsCode]
        FROM    [dbo].[SonOrder] AS [Extent1]
        INNER JOIN [dbo].[BusinessUser] AS [Extent2] ON [Extent1].[BusinessID] = [Extent2].[ID]
        LEFT OUTER JOIN [dbo].[LogisticsInfo] AS [Extent3] ON [Extent1].[LogisticsID] = [Extent3].[LogisticsID]
        INNER JOIN [dbo].[FatherOrder] AS [Extent4] ON [Extent1].[FatherOrderID] = [Extent4].[FatherOrderID]
        WHERE [Extent1].[SonOrderShow] = @p__linq__0
    )  AS [Limit1]',N'@p__linq__0 nvarchar(4000)',@p__linq__0=N'20170210165403680111702120'