On Thu, Oct 15, 2015 at 9:17 PM, Will Spurgin <will.spur...@gmail.com>
wrote:
> Hey all,
>
> I've been doing a *bunch* of researching on this topic, and I wanted to
> get feedback from the community on this potential feature (or if I'm just
> completely missing that it's already a feature, your gentle correction).
>
> Recently, I've started a project, and I ran across a scenario where I had
> to introduce duplicate scoping while defining an association. :(
>
> Here's a summary of the scenario: There is one model that has one scope
> and two associations to two other models. In one of the other models that
> the first "joining" model is associated with, I have a has_many association
> through this joined model. However, the complication (and duplication
> arises) that the association has to be scoped to the scope on the joining
> model. Currently (from what I've found through research), there's no way to
> specify an *existing scope* on a :through association. The workaround is
> to create a scope on the has_many association that does the exact same
> thing that the :through association's scope already does.
>
> An example will probably help illuminate the problem:
>
> Assume we have the following models definitions:
>
> class Book < ActiveRecord::Base
> belongs_to :author, inverse_of: :books
> belongs_to :publication, inverse_of: :books
>
> scope :published, -> { where(is_published: true) }
>
> # ...
> end
>
>
> class Author < ActiveRecord::Base
> has_many :books, inverse_of: :author
> has_many :publications, -> { where(books: { is_published: true }) },
> through: :books
>
> # ...
> end
>
>
> class Publication < ActiveRecord::Base
> has_many :books, inverse_of: :publication
>
> # ...
> end
>
>
> Notice the has_many :through association; this is currently how you'd have
> to *manually scope* the "publications" association to achieve the same
> effect of :
> publications = books.published.map(&:publication)
>
> I'd *like* to write something similar to:
> has_many :publications, through: { :books => :published }
>
>
>
I'd handle this with a specifically-named association (in `Author`):
has_many :published_books, -> { published }, class_name: 'Book'
has_many :publications, through: :published_books
You may also want to look into the documentation for the `merge` method on
Relation.
--Matt Jones
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