Left outer joins in FetchXML with multiple conditions - sql

Question

I'm trying to do a left outer join in FetchXML with multiple conditions.
Here is the approximate SQL of what I'm trying to achieve:
SELECT incident.*, externalCheck.*
FROM incident
LEFT OUTER JOIN externalCheck
ON externalCheck.incidentId = incident.incidentId
AND externalCheck.checkType = 1
AND externalCheck.isLatest = 1;
NB: This should always return a 1:1 relationship since our business logic requires that there is only one isLatest for each checkType.
And here is my FetchXML:
<entity name="incident">
<all-attributes />
<link-entity name="externalCheck" from="incidentId" to="incidentId" link-type="outer">
<filter type="and">
<condition attribute="checkType" operator="eq" value="1" />
<condition attribute="isLatest" operator="eq" value="1" />
</filter>
<all-attributes />
</link-entity>
</entity>
The Problem
The problem is that incident records where the right-hand side of the join are null (i.e. there is no externalCheck record) are not being returned, whereas in a left outer join I would expect that the incident record is still returned even if the right-hand side of the join is null.
What I suspect is that FetchXML is converting my filter to a WHERE clause, rather than adding the conditions to the ON clause.
The Question
Can anyone confirm what is happening, and a possible solution?

Answer 1

Your suspicion is correct. But you can overcome from it somewhat.
Fetchxml is flexible & the below snippet will give the results for left outer join with multiple clause.
<entity name="incident">
<all-attributes />
<link-entity name="externalCheck" alias="ext" from="incidentId" to="incidentId" link-type="outer">
<filter type="and">
<condition attribute="checkType" operator="eq" value="1" />
<condition attribute="isLatest" operator="eq" value="1" />
</filter>
</link-entity>
<filter>
<condition entityname="ext" attribute="externalCheckid" operator= "null" />
</filter>
</entity>
The real problem is with externalCheck.*, you cannot get the related entity attributes. Have to remove the <all-attributes /> from link-entity node.
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