Rails 7 adds accepts_nested_attributes_for support for delegated_type

Rails 6.1 introduced the delegated_type to Active Record, which makes it easier for models to share responsibilities. Please see our blog to read more about delegated_type.

class Entry < ApplicationRecord
  # Schema
  #  entryable_type, entryable_id, ...
  delegated_type :entryable, types: %w[ Message Comment ]
end

class Message
  # Schema
  #  subject, ...
end

class Comment
  # Schema
    #  content, ...
end

The accepts_nested_attributes_for option is very helpful while handling nested forms. We can easily create and update associated records by passing details along with the main object parameters when the accepts_nested_attributes_for option is enabled.

Before

The accepts_nested_attributes_for option is not available for delegated_type, hence we can't use nested forms for associated objects configured via delegated_type.

Rails 7 onwards

Rails 7 adds accepts_nested_attributes_for support to delegated_type, which allows to create and update records easily without needing to write specific methods or logic.

class Entry < ApplicationRecord
  delegated_type :entryable, types: %w[ Message Comment ]
  accepts_nested_attributes_for :entryable
end

params = {
  entry: {
    entryable_type: 'Message',
    entryable_attributes: { subject: 'Delegated Type' }
  }
}

message_entry = Entry.create(params[:entry])

params = {
  entry: {
    entryable_type: 'Comment',
    entryable_attributes: { content: 'Looks Cool!' }
  }
}

comment_entry = Entry.create(params[:entry])

If we want to deal with more logic or validations while creating the entryable objects, we'll have to create a method specifically and do the logic there.

class Entry < ApplicationRecord
  def self.create_with_comment(content)
    # Validation logic goes here
    create! entryable: Comment.new(content: content)
  end
end

Please check out this pull request for more details.