This content has been automatically translated from Ukrainian.
In Ruby on Rails, `has_many through` is one of the association methods that allows establishing a connection between models through another model that both have a has_many relationship.
For example, suppose you have three models: User, Role, and Assignment. The User model can have many roles, and the Role model can belong to many users. The Assignment model is used to link User and Role through the has_many through relationship.
class User < ApplicationRecord has_many :assignments has_many :roles, through: :assignments end class Role < ApplicationRecord has_many :assignments has_many :users, through: :assignments end class Assignment < ApplicationRecord belongs_to :user belongs_to :role end
In the User and Role models, we use the keyword has_many to establish an association with the Assignment model. The keyword through: :assignments tells Rails to use the Assignment model as a mediator to establish the connection between User and Role.
Now that we have this structure, we can access a user's roles through the has_many through association.
For example:
user = User.find(1) user.roles # Returns all roles associated with the user (user)
Or conversely, we can access the users that belong to a specific role:
role = Role.find(1) role.users # Returns all users that have this role (role)
has_many through allows us to conveniently work with many-to-many relationships in Ruby on Rails, simplifying access to related data through a mediator.
