ODataV4 Expand followed by Select not working

Hi There,

I am trying to run a REST query to retrieves some fields at AR Line Level (coming from ARTran) with a couple of fields coming from the ARInvoice header table.

If I start just with the AR Tran part, I have this:

/ODatav4/PX_Objects_AR_ARTran?$select=RefNbr,LineNbr&$filter=RefNbr eq 'AR012031'

which works fine.

I then try to add the expand clause to pull in the related information from AR Invoice. This gets me this:

/ODatav4/PX_Objects_AR_ARTran?$select=RefNbr,LineNbr&$filter=RefNbr eq 'AR012031'&$expand=ARInvoiceByRefNbr

which also works fine.

However - lets say I only want to see the InvoiceDate - I add a select giving me this:

/ODatav4/PX_Objects_AR_ARTran?$select=RefNbr,LineNbr&$filter=RefNbr eq 'AR012031'&$expand=ARInvoiceByRefNbr($select=InvoiceDate)

BANG!

And this rather exciting error message that I can’t make head nor tail of.

   "innererror": {

            "message": "Column DocType is not found in DAC ARRegister. ",

            "type": "PX.Data.PXNotSupportedException",

            "stacktrace": "   at PX.Data.SQLTree.SQLinqExecutor.SQLinqExpressionVisitor.VisitSubQueryProperty(SubQuery subQuery, Type dac, Type propertyType, String propertyName)\r\n   at PX.Data.SQLTree.SQLinqExecutor.SQLinqExpressionVisitor.VisitMember(MemberExpression expression)\r\n   at Remotion.Linq.Parsing.ThrowingExpressionVisitor.Visit(Expression expression)\r\n   at PX.Data.SQLTree.SQLinqExecutor.SQLinqExpressionVisitor.Visit(Expression expression)\r\n   at PX.Data.SQLTree.SQLinqExecutor.SQLinqExpressionVisitor.VisitMemberInit

etc

Any ideas?

Thanks in adavnce.

PS: Doing the same thing over SalesLines - and linking back to the header as below:

/ODatav4/PX_Objects_SO_SOLine?$select=OrderNbr,OrderDate&$filter=OrderNbr eq 'SO004375'&$expand=SOOrderByOrderNbr($select=CustomerOrderNbr)

works.

Is it possible there’s an underlying error in the join definition server side?