Question

此LINQ查询表达式发出左连接并起作用：

from p in Prices
join ip in ItemPrices 
    on new { p.PriceId,  ItemId = 7 } equals 
       new { ip.PriceId, ip.ItemId }
into priceItemPrice
from pip in priceItemPrice.DefaultIfEmpty()
select new
{
    pricesPriceId = p.PriceId,
    z = (int?)pip.PriceId,
    p.Content,
    p.PriceMinQ
}

SQL发出：

-- Region Parameters
DECLARE @p0 Int = 7
-- EndRegion
SELECT [t0].[priceId] AS [pricesPriceId], 
    [t1].[priceId] AS [z], 
    [t0].[price] AS [Content], 
    [t0].[priceMinQ] AS [PriceMinQ]
FROM [price] AS [t0]
LEFT OUTER JOIN [itemPrice] AS [t1] 
    ON ([t0].[priceId] = [t1].[priceId]) 
    AND (@p0 = [t1].[itemId])

如何让它在下面发出SQL？ 它只是在最后添加了where子句。在“from pip”下不接受where子句，并且在DefaultIfEmpty（）之前的lambda表达式不起作用。我知道我可以在选择中过滤掉它，但这不是我需要的。

SELECT [t0].[priceId] AS [pricesPriceId], 
    [t1].[priceId] AS [z], 
    [t0].[price] AS [Content], 
    [t0].[priceMinQ] AS [PriceMinQ]
FROM [price] AS [t0]
LEFT OUTER JOIN [itemPrice] AS [t1] 
    ON ([t0].[priceId] = [t1].[priceId]) 
    AND (@p0 = [t1].[itemId])
WHERE [t1].[priceId] is null

更新 Oy vey，我的错误，where子句确实有效 - 出于某种原因，VS2008没有表现出来并让我感到悲伤，我的肚子也在咆哮。我在LinqPad中测试过，where子句很好。所以这个小小的补充确实起作用了：

...
from pip in priceItemPrice.DefaultIfEmpty()
*** where pip.ItemId == null ***
select new
...

Answer 1

以下是OneDotNetWay如何做类似事情的示例。我试图采用他们的例子并匹配你的查询。

var query =  p in Prices
   join ip in ItemPrices 
   on 
   new { p.PriceId,  ItemId = 7 } 
   equals 
   new { ip.PriceId, ip.ItemId }
   into priceItemPrice
   from pip in priceItemPrice.DefaultIfEmpty()
   select new
   {
      pricesPriceId = p.PriceId,
      z = (int?)pip.PriceId,
      p.Content,
      p.PriceMinQ
   }

LINQ to SQL - 如何在左连接中添加where子句？

1 个答案: