fetchxml link-entity without alias doesn't return data

[tschopp]

When I run this query in FetchXML Builder, which has a linked-entity with no alias specified, it doesn't return the data from the linked-entity.  It returns data for "schemaname" only.  I expect it to also return data for "environmentvariablevalue1.value", but it doesn't.  The data in environmentvariablevalue exists, because if I specify an alias, the "value" values are also returned.

<fetch>
<entity name='environmentvariabledefinition'>
<attribute name='schemaname' />
<link-entity name='environmentvariablevalue' from='environmentvariabledefinitionid' to='environmentvariabledefinitionid'>
<attribute name='value' />
</link-entity>
</entity>
</fetch>

The same thing also happens sometimes (not always) when I run the same query in a C# plugin.  Any ideas on why it's working this way?

[cchannon]

As far as why, I am not sure. I think I remember from back in the 8.2 days that Fetch queries would automatically alias LEs if you didn't assign an alias yourself, so maybe you are getting a result, it's just that its name is not "value" but "SomeSystemAssignedAlias.value"

More confidently I will say--and I am sure that in general you would agree--that best practice is to always alias your linked entities if for no reason other than the disambiguation of columns with same or similar naming. Is there some reason why you are not aliasing your LEs?

[skoofy5]

@cchannon is right - see this for details https://community.dynamics.com/blogs/post/?postid=a08dd1d8-09af-4ca2-88e6-0e4996c687fc#:~:text=The%2....

I believe one of the reasons for this is to ensure that any duplicate column names on the linked entity can be differentiated without error.

[cchannon]

Nice - thanks for the confirm @skoofy5 !

[tschopp]

@cchannon @skoofy5 

I agree the LE should have an alias on it.  That C# code was written a couple years back when I was new to Power Apps.  We still have some older versions of it out there that relied on "If you do not provide an alias, the platform will auto generate the alias for you" and have always worked until now.  I'm wondering if something changed recently that require an alias be assigned

[skoofy5 · Accepted solution]

It's difficult to say what's going on without more information.

Perhaps you were applying an alias to the attribute? *Edit* For others reading this don't forget that with fetch calls when the value you want doesn't exist it omits it in the object entirely (please also note the generated alias):

//generated alias

{
    "@odata.etag": "tag",
    "schemaname": "schema",
    "environmentvariabledefinitionid": "id",
    "environmentvariablevalue1.value@OData.Community.Display.V1.AttributeName": "value",
    "environmentvariablevalue1.value": "value"
}

//null in value attribute returns nothing

{
    "@odata.etag": "tag",
    "schemaname": "schema",
    "environmentvariabledefinitionid": "id"
}

//providing an alias for the linked-entity attribute returns the alias without the prefix
//<attribute name="value" alias="valueAlias" />

{
    "@odata.etag": "tag",
    "schemaname": "schema",
    "environmentvariabledefinitionid": "id",
    "valueAlias@OData.Community.Display.V1.AttributeName": "value",
    "valueAlias": "value"
}

 
While with an OData call the attribute is returned even when null.

		{
			"@odata.etag": "tag",
			"schemaname": "schema",
			"environmentvariabledefinitionid": "id",
			"environmentvariabledefinition_environmentvariablevalue": [
				{
					"@odata.etag": "tag",
					"value": null,
					"_environmentvariabledefinitionid_value": "id",
					"environmentvariablevalueid": "id"
				}
			]
		},

 
FetchXML Builder also warns you now that an alias is required, because it's the correct practice - you should not rely on a system generated alias. Relying on a generated alias is going to make interrogating those values meaningless without it.

[tschopp]

I created a patch release of our plugin that has the alias added for the link-entity and it's working now.  I'm just puzzled why it stopped working in the one environment while it continues to work in others

[cchannon]

So it turns out that there HAVE been recent changes to Fetch. Mark Carrington just blogged about it here. Not clear to me why any of these updates would have caused your issue; probably just an undocumented change that went along with their announced updates.

[skoofy5]

I understand the frustration! We're currently having issues with plugins duplicating create calls. Plugin has been there for years, but in the last month we've started seeing duplicates. It's good that you seem to have a solution - hope it works out for you.