Not 100% sure of where the issue is, but it seems to come up with has_many associations.

If I have a scope in a Foo model (where a user has_many: foos) - models/foo.rb:

belongs_to :user
scope :hasCars, -> { joins(:cars) }

And now try use the scope with will_paginate (in the controller):

@foos = auser.foos.hasCars.paginate(:page=>1,:per_page=>20)

Then the view duplicates each foo by the number of cars they have in the :through ownership association - so if auser.foos.first has 3 cars. foos.first will be iterated through 3 times in the paginated view.

I can work around this by using a group:

@foos = auser.foos.hasCars.group("car_id").paginate

http://stackoverflow.com/questions/38671915/rails-will-paginate-with-named-scope-for-associations-0/38671965#38671965

http://stackoverflow.com/questions/11729816/rails-will-paginate-shows-duplicates-on-habtm-models