Merge A Scope Into An ActiveRecord Query

Consider an ActiveRecord model with a scope:

class Book < ApplicationRecord
  scope :published, -> { where("books.published_at is not null") }
end

Now let's say we are working in another part of the codebase composing a query that gathers all authors with published books. That might look something like this:

published_authors =
  Authors.joins(:book).where("books.published_at is not null")

This will get the job done, but we've now duplicated the same logic in different parts of the app. We can utilize the existing scope on Book using ActiveRecord's merge method.

published_authors =
  Authors.joins(:book).merge( Book.published )

The merge method can be used to incorporate any conditions from other partial queries -- this means both where clauses and joins clauses.

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