I think your issue is that when you pick your list view over an association you don't get search filter abilities? If thats the case, you can set the source to be xpath, and the very top of the list, it will show the dataview object (in this case project), and when you expand that, you can click the association location. This will display the list of associated locations, while having functionality to search them.
I created a small model with 2 entities: Project and Location. I also created a many to many association between those entities.
Next, I created a page with a List View of Project, and nested in that List View, another List View of Location.
Here is a screen shot of that page from the Modeler:
The data source for the nested List View looks like this
Once I start the app, the page looks like this:
The search box above (from the Location List View), will only search within those Locations that are associated with Project 1.
Is this what you are trying to accomplish? Or is it something different than this?
I need the location list to be associated to a single project, so I am using a Data View for the Project that is selected on the page. (I'm open to alternative methods).
If I set my Location List to xpath, I have the ability to search, however, this will show and search on locations for all projects.
If I set my Location List to associated (to the project), the search is lost.