Ruby on Rails: Is there a way to temporarily disable polymorphic associations?

I've got an association between models that is polymorphic.

Example:

class Review
  belongs_to :review_subject, :polymorphic => true
end

However, I would like to make a call on this :review_subject association where I know all the results will be of a certain type.

In my case, I want to do this so I can join in the review_subject and then impose a condition upon it. Doing so on a polymorphic relation normally causes this to raise an EagerLoadPolymorphicError. The logic behind this is that it's not able to know what model to load in order to perform the join, but that does not apply in my case because I already know only one model will be involved in this query.

Example, where I know that all relevant reviews will belong_to a Book, and I want to only show reviews where the books have authors:

Review.joins(:review_subject)
      .where(review_subject_type => "Book")
      .where("reviewed.book_author IS NOT NULL")开发者_C百科

Is there a way to temporarily disable the polymorphic relationship?

The best solution I've come up with is to add a second associationin the Review model, belongs_to :review_subject_books_only that is not polymorphic, and can be called on only in this situation. However, this is an ugly hack both in the model, and in that it also messes up include calls unless the views also refer to a Review's review_subject_books_only.

Do the query the other way around:

Book.joins(:reviews).where('book_author is not null')