I have a 2 entities for my practice project:

Visitor Entity composed of 




Signature Entity composed of 



VisitorId (foreign key from Visitor Entity)

I wish to display the signature on an image widget based on the Signature Entity's VisitorId, and not on Signature Entity's SignatureId

Thanks in advance.

You could query Signature Entity on a Preparation to fetch SignatureId based on a VisitorId and then use it as Entity Identifier of Image widget.

Another approach is to replace SignatureId to be of Visitor Identifier type, this way you will have 1:1 relation and could use same VisitorId to fetch required Signature. I would say this approach might be better as chances to have 2 signatures at the same time are quite low.