Question

I’m racking my brain on this complex query for finding related posts:

Here’re my models:

class Post
   has_many :post_assignments, :dependent => :destroy
   has_many :topics, :through => :post_assignments
end

class PostAssignment
   belongs_to :post
   belongs_to :topic
end

class Topic
  has_many :post_assignments, :dependent => :destroy
  has_many :posts, :through => :post_assignments
end

Given that I have a post that may or may not have a topic. I need to find all posts that share a topic in common with this one.

I am already using the squeal gem so that syntax would be preferable.

Answer 1

Sorry I haven’t used the sequeal gem, so don’t know its syntax. I think this would work, but it might not be the best way:

@post.topics.map(&:posts).flatten.uniq

Another way I can think of:

Post.joins('LEFT OUTER JOIN post_assignments ON post_assignments.post_id = post.id LEFT OUTER JOIN topics on post_assignments.topic_id = topic.id').where(:topic_id => @post.topics.map(&:id)) 

Lastly, you could write the SQL.