Good day

I would like to know how one could filter the values that are displayed in a drop down in a form. This is a detail form used to capture details of an entity and then submit them to the DB. The drop down displays the results of an entity, but the entity has a foreign key in it. Clicking on the drop down only allows access to the source entity and attribute its this source that I need to filter.

Perhaps the autocomplete component of the forge is something you could use.
That will help if the user know what they are looking for but not when need to pick from a list.