CODEWITHSUNDEEP
ruby-on-railsruby-on-rails-3postgresqlactiverecord
1dolinski
1dolinski

Reputation: 549

Rails joins query

I have three models

I know the id of the tag. I would like to query for all of the posts that have a specific tag_id, through the Taggings model.

Something like

@post = Post.joins(:taggings).where(:tag_id => 17)

but this doesn't work because it is looking for the tag_id in the Post model and not the Tagging model.

I'm not sure how to do this.

Upvotes: 3

Views: 20203

Answers (4)

1dolinski
1dolinski

Reputation: 549

As @tharrison mentioned. A solution is:

@post = Post.joins(:taggings).where("taggings.tag_id = ?", 17)

Upvotes: 1

Raphael Abreu
Raphael Abreu

Reputation: 211

I don't like to use string in ActiveRecord queries, so, I prefer this sintax:

@post = Post.joins(:taggings).where(taggings: {tag_id: 17})

Upvotes: 17

Alexandru Emil Lupu
Alexandru Emil Lupu

Reputation: 429

First of all :

 class Post < ActiveRecord::Base

   has_many :taggings
   has_many :tags, :through => :taggings 
 end

 class Taggins < ActiveRecord::Base 
   belongs_to :post 
   belongs_to :tag
 end

 class Tag < ActiveRecord::Base 
   has_many :taggings 
   has_many :posts, :through => :taggings 
 end

If you have the tag object you can do 

 @posts = @tag.posts

or 

 class Post < .... 
   ....
   def self.find_by_tag_id(tag_id)
      Post.joins(:taggings).where('taggings.tag_id = ?', tag_id)
   end
 end

Upvotes: 7

Tom Harrison
Tom Harrison

Reputation: 14018

Using the .where format you can pass a string like .where("taggings.tag_id = ?", 17) to qualify the joined taggings table.

Upvotes: 2

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