In my previous post Virtual Entities I walked through the steps of creating a Virtual Entity using the data source "http://services.odata.org/V4/OData/OData.svc"
Another open data source is "http://api.purdue.io/odata" (publicly accessible), which lets us leverage a 1:n many relationship that exists between (course-) subjects and courses in that provider to create and relate two virtual entities.
So if I create a parent (virtual) entity called CourseSubject and a related (virtual) entity called Course I can demostrate another aspect of the power of virtual entities - relationships
If I click I see all the (course-) subjects listed in a nice grid...
I can click one of the subjects, eg "American Studies" to open the form...
In the form, I can navigate to the related views to see the all the Courses related to the Subject American Studies...
In the list of courses related to subject American Studies I can click a Course...
And in the opened form I can see the lookup field from the relationship with the Subject
To make this work it is important you ensure that the external name of the lookup field matches the external name from the data source entity
With Virtual Entities you can surface data from external data sources in Dynamics 365 and work with the data as entities without the data residing in Dynamics 365