I have created a view that filters out entities that have an existing relationship for Referencing entity. Basically show only where nid of referencing entity is null. This works until I try to actually add a new reference to a node. I get an error for the existing entities when I try to add another. I also tried using tokens to add a conditional class to hide, which it does, but only the text. Users are still able to select entities by selecting the seemingly empty space in the drop down. I can't get to the parent in container in the drop down to hide.

The reason I need this is that I want to try and ensure that an entity is only referenced once. There is nothing available to enforce this, so my next best option was to not show entities already referenced.

Maybe something exists that I missed. If not, is there anyway to make this work with a view?

Thank you,
Sean