我不擅长
Linq表达,今天我遇到了一个奇怪的问题,如下面的内连接语句,
var orders = (from q in dao.CurrentDBContext.New_OrderForm
join d in dao.CurrentDBContext.New_OrderGoodsDetail on q.billNum equals d.billNum
select new
{
q.billNum,q.orderSource,q.sourceOddNum
d.PPT
}
当我追踪linq语句时,我很困惑,实体框架会将linq语句转换为下面的sql语句
SELECT
[Extent1].[billNum] AS [billNum],[Extent1].[orderSource] AS [orderSource],[Extent1].[sourceOddNum] AS [sourceOddNum],[Extent2].[PPT] AS [PPT]
FROM [dbo].[New_OrderForm] AS [Extent1]
INNER JOIN [dbo].[New_OrderGoodsDetail] AS [Extent2]
ON ([Extent1].[billNum] = [Extent2].[billNum]) OR
(([Extent1].[billNum] IS NULL) AND ([Extent2].[billNum] IS NULL))
你知道为什么下面的sql段会自动附加吗？
或(([Extent1].[billNum] IS NULL)AND([Extent2].[billNum] IS NULL)“
我不希望上面的内容自动附加,因为它确实降低了sql性能.有什么建议？
解决方法
如果您无法将billNum列更改为不可为空,则可以执行以下操作.
首先,设置@Giorgi提到的选项
class CurrentDBContext
{
public CurrentDBContext()
{
Configuration.UseDatabaseNullSemantics = true;
// ...
}
}
然后将LINQ查询更改为不使用join,但这样简单
var orders = (from q in dao.CurrentDBContext.New_OrderForm
from d in dao.CurrentDBContext.New_OrderGoodsDetail
where q.billNum == d.billNum
select ...
结果将是您所显示的(使用JOIN！)而没有OR部分的确切SQL查询.