App: use disaplay template fields as a supplementary query fields in relateion interface

[everyx]

I want show product_property_items_id.property.name and product_property_items_id.value so I set this in this many to many relation, but is empty when I view product item

apps should consider adding flexibility in this case.

[rijkvanzanten]

Yes! Yes! Yes!

As a matter of fact, I actually just implemented this and got it working in the v9 in works branch 😄

The display template for m2o can go indefinitely deep in v9+ 💪