It's so nice to be able to say that my Videos belongs to many tags! So clear and simple! Love it!

Belongs to an array of records, storing those locally. The original belongs_to associations define a SingularAssociation, which means that it could be extended with array: true. In this case, I decided to create my own CollectionAssociation called belongs_to_many, which behaves similar to the single one, but storing and returning a list of records. This was only possible due to PostgreSQL arrays and the new Arel inflix operators.

With this, now you can say things like Project belongs to many employees, which is more syntactically correct than Project has many employees PostgreSQL Docs

How it works

Migration

The only difference here while creating the association is that you just need to set the column as an array. The references or similar helpers are not yet available.

create_table "employee" do |t|
  t.string "name"
end

create_table "project" do |t|
  t.bigint "employee_ids", array: true
  t.string "title"
end

Model

Now go to the model and simply activate the feature using the belongs_to_many method, similar to how would you do with belongs_to.

# models/project.rb
class Project< ApplicationRecord
  belongs_to_many :employees
end

That's it. The features provided with this is a middle point between belongs_to and has_many, which means that the records are returned as a list on CollectionProxy, but things like touch are also available.

One important notice is that polymorphic is not allowed for array-like associations, because the tuples can be guaranteed every time.

Most of the options are just like the has_many association, but it also includes:

• touch: If true, the associated objects will be touched (the updated_at/on attributes set to current time) when this record is either saved or destroyed. Default: false
• optional: When set to true, the association will not have its presence validated. Default: true
• required: When set to true, the association will also have its presence validated. Default: false
• dependent: Controls what happens to the associated objects when their owner is destroyed. Default: :nullify
• primary_key: The name of the array column used to store the association ids locally. Default: :"#{name.singular}_ids"
• foreign_key: The name of the column that on the foreign table that connects to the array. Default: :id

There are no additional or custom feature on top of those provided by a normal has_many association.