获取特定类型的多态关联

Question

I have this model

class Article
  belongs_to :source, polymorphic: true
  belongs_to :html, foreign_type: "Html", foreign_key: "source_id"
  belongs_to :pdf, foreign_type: "Pdf", foreign_key: "source_id"
end

When I set an article with an html source, pdf is still found when html and pdf have the same id :

html.id
=> 1
pdf.id
=> 1

article = Article.create!(source: html)
article.pdf.id
=> 1

What am I doing wrong? Isn't the foreign_type that tells Rails what to match for the polymorphic association?

Answer 1

According to APIdock:

:foreign_type

Specify the column used to store the associated object's type, if this is a polymorphic association. By default this is guessed to be the name of the association with a “_type” suffix. So a class that defines a belongs_to :taggable, polymorphic: true association will use “taggable_type” as the default :foreign_type.

So, you should use foreign_type in the source association to specify what column stores the associated object's type.

I think you want two methods html and pdf , so you can use it when the source is either Html or Pdf . In this case, I think you should create two methods for it, for example:

def html
  source if source_type == "Html"
end


def pdf
  source if source_type == "Pdf"
end