与条件的多态关联

Question

我们有以下型号...

class Post
  has_many: :comments, as: :commentable
end

class Media
  has_many: :comments, as: :commentable
end

class Comment
  belongs_to: :commentable, polymorphic: true
  belongs_to: :post, foreign_key::post_id, foreign_type: 'Post'
end

示例

Post1 has Comment3 => {id: 3, text: "Some comment 3", commentable_id: 1, commentable_type: 'Post'}
Media2 has Comment4 => {id: 4, text: "Some comment 4", commentable_id: 2, commentable_type: 'Media'}

When I want to access Comment3.post it gives result as expected.
But When some how want access Comment4.post it brings an object from post table which has id = 2, but expected nil, coz Comment4 does not belongs to any post.

我们可以从 Comment 模型中的以下方法获取，但需要作为关联。

def post
  self.commentable if self.commentable_type == 'Post'
end

无法达到我的预期..，请在这里帮忙...

Answer 1

我喜欢你的做法

def post
  self.commentable if self.commentable_type == 'Post'
end

但是如果你真的需要关联方式，那么你可以试试

belongs_to :post, foreign_key: :commentable_id, foreign_type: :commentable_type, polymorphic: true

或

belongs_to :post, -> (record){ record.commentable_type == 'Post' ? joins(:comments).where(comments: {commentable_type: 'Post'}) : where("false") }, foreign_key: :commentable_id

希望对您有帮助。