CODEWITHSUNDEEP
ruby-on-railsactiverecordassociations
Alien
Alien

Reputation: 1162

Rails has_many association how to guarantee only one of each associated record?

I have this system essentially:

class Article < ApplicationRecord
  has_many :tag_associations
  has_many :tags, through :tag_associations
end

class Tag < ApplicationRecord
  # attr :name
end

How do I make it so the article can only have one of each tag name? That is, say I have these tags:

{ name: 'foo' }
{ name: 'bar' }
{ name: 'baz' }

I would eexpect this to be the final result:

tag1 = Tag.create!(name: 'foo')
tag2 = Tag.create!(name: 'bar')
tag3 = Tag.create!(name: 'baz')
article.tags << tag1
article.tags << tag2
article.tags << tag1
article.tags << tag1
article.tags << tag1
article.save!
article.tags # => [tag1, tag2]

How do I achieve this? I am not highly familiar with Rails paradigms, and am not really sure how to do this in a general way even with plain SQL. But I am just looking for how to do this the Rails way.

Upvotes: 0

Views: 75

Answers (1)

Les Nightingill
Les Nightingill

Reputation: 6156

It's done using an ActiveRecord uniqueness validation.

In this case, I would suggest that the validation should be applied in the ArticleTag model. Create this model if you don't already have it.

class ArticleTag < ActiveRecord::Base

  validates :tag_id, :uniqueness, scope: :article_id

end

This says that instances of ArticleTag with associated with a given Article should have unique tag_id. So if you try to create a duplicate tag for an articl, you'll raise a validation error.

Upvotes: 1

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