Multiple has_many relationships to same model

问题

I have a model User that can create Posts

User
 has_many :posts
Post
 belongs_to :user

However, I want to also allow users to save posts as bookmarks. So I added the following:

Bookmark
 belongs_to :post
 belongs_to :user
User
 has_many :posts
 has_many :posts, :through => :bookmarks
Post
 belongs_to :user
 has_many :posts, :through => :bookmarks

This can't be right because it is now ambiguous when I do @user.posts . Does that refer to the posts the user wrote or the posts the user bookmarked?

How do you get around this problem?

回答1:

How do you get around this problem?

By giving your associations unique names. It's not that you can't unambiguously access them, it's that your second one is destroying the first one.

Instead of calling both posts, use bookmarked_posts for your second association:

has_many :bookmarked_posts, through: :bookmarks, source: :posts

回答2:

Maybe something like this?

User
  has_many :bookmarks
  has_many :posts, through: :bookmarks
  has_many :authored_posts, foreign_key: :author_id, class_name: 'Post'
Bookmark
  belongs_to :post
  belongs_to :user
Post
  belongs_to :author, class_name: 'User'
  has_many :bookmarks
  has_many :users, through: :bookmarks

In this way, you are able to keep posts that are written by and bookmarked by a user separate. You could also set it up so that whenever an author creates a post, it can automatically get bookmarked by the user. i.e.

class PostsController < ActionController::Base
  def create
    @post = @user.authored_posts.build(post_params)
    @user.posts << @post

    if @post.valid?
      # do good stuff
    else
      # do errors
    end
  end
end

There is a strong 1:N relationship between author and authored_posts. Then there is a weaker N:M relationship between Users and Posts using Bookmark as the join model. You can add authored posts to be bookmarked when they are created using the controller code above. Removing a bookmark on an authored post will simply remove it from the posts relationship, but not the authored_posts relationship.

You cannot define multiple relationships using the same name.

回答3:

Check the rails API on this. You should be able to specify :as and :source

来源：https://stackoverflow.com/questions/18690700/multiple-has-many-relationships-to-same-model

标签

ruby-on-rails

activerecord