Rails 5.2 eager load polymorphic nested

Question

Is it possible to eager load polymorphic nested associations? How can I include doctor_profile's for Recommendation's and patient_profile's for Post's?

I'm able to call Activity.includes(:trackable).last(10) but not sure how to include the associated models past there. I've tried belongs_to :recommendation, -> { includes :patient_profile, :doctor_profile} with no luck

class Activity
  belongs_to :trackable, polymorphic: true

end

class Recommendation
  has_many :activities, as: :trackable
  belongs_to :doctor_profile

end

class Post
  has_many :activities, as: :trackable
  belongs_to :patient_profile

end

widjajayd · Accepted Answer · 2019-02-20T16:21:27.913

2

with respect referenced this SO answer and comments for your problem you can managed with foreign_type field from polymorphic table to reference which model that use it

class Activity
  belongs_to :trackable, polymorphic: true
  # below is additional info
  belongs_to :recommendation, foreign_type: 'Recommendation', foreign_key: 'trackable_id'
  belongs_to :post, foreign_type: 'Post', foreign_key: 'trackable_id'
end

and you can call it

Activity.includes(recommendation: :doctor_profile).last(10)
Activity.includes(post: :patient_profile).last(10)

Activity.includes(recommendation: :doctor_profile) means

Activity will join recommendation with foreign_type and trackable_id
and then from recommendation will join doctor_profile with doctor_profile_id

edited Feb 20 '19 at 16:21

answered Feb 20 '19 at 01:52

widjajayd

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thanks. is it possible to do the includes in 1 call? – user2954587 Feb 20 '19 at 14:13
you can try it first, I edited my answer to add some explanation about includes in one call – widjajayd Feb 20 '19 at 16:22
1

you can. thank you - `Activity.includes(recommendation: :doctor_profile, post: :patient_profile).last(10)` – user2954587 Feb 20 '19 at 16:38

score 0 · Answer 2 · answered Dec 10 '20 at 22:49

The above answer works, but the use of foreign_type isn't actually supposed to do what the commenter intended.

https://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

foreign_type is used to specify the name for the column which determines the class type for the relation.

I think the intended result here is to instead use class_name to specify which table the relation is referring to. If the relation has the same name as the table, then class_name can actually be inferred (which is why the provided answer works in the first place)

score 0 · Answer 3 · answered Jan 07 '21 at 23:05

In order to get the above answer to work, specifying inverse_of for the belongs_to and adding for the has_many associations got everything to work. For example:

class Activity
  belongs_to :trackable, polymorphic: true
  # below is additional info
  belongs_to :recommendation, foreign_type: 'Recommendation', foreign_key: 'trackable_id', inverse_of: :activities
  belongs_to :post, foreign_type: 'Post', foreign_key: 'trackable_id', inverse_of: :activities
end

On the Post model:

has_many :activities, inverse_of: :post

On the Recommendation model:

has_many :activities, inverse_of: :recommendation

Rails 5.2 eager load polymorphic nested

3 Answers3