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Rails 7 allows constructors (build_association and create_association) on has_one :through associations
What are build_association and create_association constructors?
When we declare either a belongs_to or has_one association,
the declaring class automatically gains the following methods
related to the association:
- build_association(attributes = {})
- create_association(attributes = {})
In the above methods
_association is replaced with the symbol(association name)
passed as the first argument while declaring the associations.
For example:
1class Book < ApplicationRecord
2 belongs_to :author
3end
4
5@book.build_author(name: 'John Doe', email: 'john_doe@example.com')
6#=> Returns a new Author object, instantiated with the passed attributes
7#=> Links through the book's object foreign key
8#=> New author object won't be saved in the database
9
10@book.create_author(name: 'John Doe', email: 'john_doe@example.com')
11#=> Returns a new Author object, instantiated with the passed attributes
12#=> Links through the book's object foreign key
13#=> The new author object will be saved in the database after passing all of the validations specified on the Author modelBefore Rails 7
The build_association and create_association constructors
were only supported by
belongs_to and has_one associations.
Consider the example below.
We have a model, Member,
that has a has_one association
with the CurrentMembership model.
It also has a has_one :through association
with the Club model.
1class Member < ApplicationRecord
2 has_one :current_membership
3 has_one :club, through: :current_membership
4end
5
6@member.build_club
7#=> NoMethodError (undefined method `build_club' for #<Member:0x00007f9ea2ebd3e8>)
8#=> Did you mean? build_current_membership
9
10@member.create_club
11#=> NoMethodError (undefined method `create_club' for #<Member:0x00007f9ea2ebd3e8>)
12#=> Did you mean? create_current_membershipAfter Rails 7
Users are allowed to use constructors
(build_association and create_association)
on has_one :through associations
along with belongs_to and has_one associations.
1class Member < ApplicationRecord
2 has_one :current_membership
3 has_one :club, through: :current_membership
4end
5
6@member.build_club
7#=> #<Club:0x00007f9ea01a8ce0>
8
9@member.create_club
10#=> #<Club:0x00007f9ea01a8ce0>Check out this pull request for more details.
