Rails 5 get association of association

Question

Rails 5, using filterrific to filter a model with a polymorphic association on an association attribute.

Flag
  belongs_to :flaggable, polymorphic: true
  belongs_to :reporter, class_name: "User"

Post
 belongs_to :user
 has_many :flags, as: :flaggable

Comment
 belongs_to :user
 has_many :flags, as: :flaggable

For filteriffic to work, it needs a scope defined on the model, and I'm trying to get any flagged post or comment that belongs to a certain user. flag.flaggable.user.id works correctly, but I can't seem to get the scope right.

scope :with_owner_name, lambda { |post_owner|
    includes(flaggable: :user).where( :post => {:user => [*post_owner]} )
  }

or

scope :with_owner_name, lambda { |post_owner|
        includes(flaggable: :user).where( :flaggable => {:user => [*post_owner]} )
      }

returns

Cannot eagerly load the polymorphic association :flaggable

and trying to include each flaggable model individually does the same. Is there even a way to do this? I can't find anything in filterrific's documentation about polymorphic scopes. Should I instead have an association between Flag and the Post/Comment user?

Answer 1

This is not a filterrific specific issue. Working with polymorphic relations can be a pain to work with, I've had similar cases and I think I did a manual join to fix this in the end.

Can you try if this works?

joins("INNER JOIN flags ON flags.flaggable_id = posts.id AND flags.flaggable_type = 'Post' INNER JOIN users ON users.id = flags.user_id")

E.g.

scope :with_owner_name, lambda { |post_owner|
    joins("INNER JOIN flags ON flags.flaggable_id = posts.id AND flags.flaggable_type = 'Post' INNER JOIN users ON users.id = flags.user_id").where( :post => {:user => [*post_owner]} )
}