Question

So basically, I try here to transfer this query in LINQ.

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'

I know for the most part that the query should look like something like that:

(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
});

The part here where I’m really not sure is the “ApplicationMessageTypes” part. For a multiple left join query I’d use the new {} equals new {} construct but in this case, I have 2 clauses ( [AMT].[ApplicationID] = @p1 OR [AMT].[ApplicationID] IS NULL ).

Should I use something like new { mt.MessageTypeID, new { applicationId ,null }} equals new { amt.MessageTypeID, amt.ApplicationID }? This seems too strange to be real.

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
});