Rails includes with scope

Question

I have a model called Author. An author has many Articles. Articles have a scope called .published that does: where(published: true).

I want to load the author, with the published articles. I tried:

Author.includes(:articles.published).find(params[:author_id])

But that throws an error: undefined method 'published'. Any idea?

Solution 1

I think the best solution would be:

Author.includes(:articles).where(:articles=>{published: true}).find(params[:author_id])

Or you can create scope:

class Author < ActiveRecord::Base 
    scope :with_published_articles, -> { includes(:articles).where(articles: { published: true}) }
end

and then:

Author.with_published_articles.find(params[:author_id].to_s)

Solution 2

I would specify a scope on the Author called with_published_articles like this:

scope :with_published_articles, -> { joins(:articles).merge(Article.published) }

This will resolve your problem to also specify the where(active: true) on your Author model in case the published behaviour of and Article will change in the future.

So now you can call:

Author.with_published_articles.find(params[:author_id])

Solution 3

Using:

class Articles < ActiveRecord::Base 
    scope :published, -> { where(articles: {published: true}) }
end

Define a scope on Autor

class Author < ActiveRecord::Base 
    scope :with_published_articles, -> { joins(:articles).merge(Articles.published) }
end

Or

Author.joins(:articles).merge(Articles.published).find(params[:author_id])

Solution 4

Try this code:

Author
  .includes(:articles).where(published: true).references(:articles)
  .find(params[:author_id])

Here you can find more information about the example above: includes api doc

View more solutions

Comments

[tantrix]

This is the best answer since it doesn't couple Author with Article's internal implementation of what "published" means

[Joel Blum]

As far as I know joins does not eager load, so this will still have n+1 problem

[Midwire]

This is the correct answer because it decreases future cost-of-change (avoiding code duplication and leaking implementation details of the concept of a published Article). And as tantrix said, it also avoids further coupling of Author and Article.