使用“或”子句的LINQ多个左外连接

Question

所以基本上，我尝试在LINQ中传输此查询。

DECLARE @p1 UniqueIdentifier SET @p1 = 'AC1D85C1-28F1-46A3-9C6A-3B7446609A2A' 
DECLARE @p2 UniqueIdentifier SET @p2 = NEWID() 
SELECT 
    [MTD].[Description], 
    [MTD].[MessageTypeID], 
    ISNULL([AMT].[ApplicationMessageTypeID], NEWID()), 
    ISNULL([AMT].[EventForwardingRuleID], '1001') 
FROM [dbo].[MessageType] as [MT] 
INNER JOIN [dbo].[MessageTypeDescription] AS [MTD] 
     ON [MT].[MessageTypeID] = [MTD].[MessageTypeID] 
LEFT OUTER JOIN [dbo].[ApplicationMessageType] AS [AMT] 
     ON [AMT].[MessageTypeID] = [MT].[MessageTypeID] 
     AND ([AMT].[ApplicationID] = @p1 OR [AMT].[ApplicationID] IS NULL) 
WHERE [MTD].[Culture] = 'fr' 

我知道大部分的查询看起来应该像这样的事情：

(from mt in db.MessageTypes 
join mtd in db.MessageTypeDescriptions 
    on mt.MessageTypeID equals mtd.MessageTypeID 
join amt in db.ApplicationMessageTypes 
    on new { mt.MessageTypeID, (applicationId || null) } equals new { amt.MessageTypeID, amt.ApplicationID } 
    into appMessageTypes 
from amt in appMessageTypes.DefaultIfEmpty() 
where mtd.Culture == culture 
select new ApplicationEditEventTypeModel 
{ 
    ApplicationMessageTypeID = amt.ApplicationMessageTypeID == null ? Guid.NewGuid() : amt.ApplicationMessageTypeID, 
    Description = mtd.Description, 
    MessageTypeID = mtd.MessageTypeID, 
    EventForwardingRuleID = amt.EventForwardingRuleID == null ? 0 : amt.EventForwardingRuleID 
}); 

在这里，我真的不知道该部分是“ApplicationMessageTypes”的一部分。对于多个左连接查询，我会使用new {} equals new {}构造，但在这种情况下，我有2个子句([AMT].[ApplicationID] = @p1 OR [AMT].[ApplicationID] IS NULL)。

我应该使用类似new { mt.MessageTypeID, new { applicationId ,null }} equals new { amt.MessageTypeID, amt.ApplicationID }的东西吗？这似乎太奇怪，不真实。

Answer 1

(from mt in db.MessageTypes 
join mtd in db.MessageTypeDescriptions 
    on mt.MessageTypeID equals mtd.MessageTypeID 
from amt in db.ApplicationMessageTypes 
    .Where(a => a.MessageTypeID == mt.MessageTypeID && 
      (a.ApplicationID == applicationId || !a.ApplicationID.HasValue)).DefaultIfEmpty() 
where mtd.Culture == culture 
select new ApplicationEditEventTypeModel 
{ 
    ApplicationMessageTypeID = amt.ApplicationMessageTypeID ?? Guid.NewGuid(), 
    Description = mtd.Description, 
    MessageTypeID = mtd.MessageTypeID, 
    EventForwardingRuleID = amt.EventForwardingRuleID ?? 0 
}); 

Answer 2

我认为ApplicationId子句看起来并不像它的JOIN部分 - 即它不是外键关系的一部分 - 相反它实际上只是一个正常的WHERE条件。

所以我建议你移动的applicationID出其中两个SQL和LINQ的

DECLARE @p1 UniqueIdentifier SET @p1 = 'AC1D85C1-28F1-46A3-9C6A-3B7446609A2A' 
DECLARE @p2 UniqueIdentifier SET @p2 = NEWID() 
SELECT 
    [MTD].[Description], 
    [MTD].[MessageTypeID], 
    ISNULL([AMT].[ApplicationMessageTypeID], NEWID()), 
    ISNULL([AMT].[EventForwardingRuleID], '1001') 
FROM [dbo].[MessageType] as [MT] 
INNER JOIN [dbo].[MessageTypeDescription] AS [MTD] 
     ON [MT].[MessageTypeID] = [MTD].[MessageTypeID] 
LEFT OUTER JOIN [dbo].[ApplicationMessageType] AS [AMT] 
     ON [AMT].[MessageTypeID] = [MT].[MessageTypeID] 
WHERE [MTD].[Culture] = 'fr' 
     AND (AMT IS NULL OR ([AMT].[ApplicationID] = @p1 OR [AMT].[ApplicationID] IS NULL)) 

和

(from mt in db.MessageTypes 
join mtd in db.MessageTypeDescriptions 
     on mt.MessageTypeID equals mtd.MessageTypeID 
join amt in db.ApplicationMessageTypes 
     on new mt.MessageTypeID equals amt.MessageTypeID 
    into appMessageTypes 
from amt in appMessageTypes.DefaultIfEmpty() 
where mtd.Culture == culture 
     && amt==null || (amt.ApplicationID == null || amt.ApplicationID == applicationId) 
select new ApplicationEditEventTypeModel 
{ 
ApplicationMessageTypeID = amt.ApplicationMessageTypeID == null ? Guid.NewGuid() : amt.ApplicationMessageTypeID, 
Description = mtd.Description, 
MessageTypeID = mtd.MessageTypeID, 
EventForwardingRuleID = amt.EventForwardingRuleID == null ? 0 : amt.EventForwardingRuleID 
}); 

你也许还使用了嵌套查询（或视图）如果您想要使ApplicationId子句更接近原始ApplicationMessageType表