Add :extractor option to ::association

[hugopeixoto]

I have the following use case (code simplified for readability):

# BlueprinterFinder#find converts :user into UserSerializer

class ApplicationSerializer < Blueprinter::Base
  def self.association(method, options = {}, &block)
    super(
      method,
      { blueprint: BlueprinterFinder.find(method) }.merge(options),
    )
  end
end

class UserSerializer < ApplicationSerializer
  association :contents do |user, options|
    if options[:version]
      user.content_versions.find_by!(version: options[:version])
    else
      user.content_versions.last
    end
  end
end

class UsersController
  def show
    render json: UserSerializer.render(User.find(params[:id]), version: params[:version])
  end
end

I also needed something like the following:

class CredentialSerializer < ApplicationSerializer
  association :user # pass in credential.version to UserSerializer#render somehow
end

class CredentialsController
  def show
    render json: CredentialSerializer.render(Credential.find(params[:id]))
  end
end

To do this, I tried to override the extractor on the association:

class MyAssociationExtractor < Blueprinter::AssociationExtractor
  def extract(association_name, object, local_options, options={})
    super(
      association_name,
      object,
      local_options.merge(version: object.version),
      options.except(:extractor),
    )
  end
end

class CredentialSerializer < ApplicationSerializer
  association :user, extractor: MyAssociationExtractor
end

::field allows to override the :extractor option, but ::association does not. This PR introduces the ability to override :extractor in associations as well.

Sidenotes/questions:

Is there another way of specifying local_options on associations that I may have missed?

I noticed that apart from the extractor, the differences between ::association and ::field is the option association: true. This option seems to be used in Blueprinter::BaseHelpers#associations, but I don't see where this helper is used. Is it still required?

[philipqnguyen]

Thank you @hugopeixoto !! Yes I think this makes perfect sense and makes the association method more aligned with the rest of the api.

My responses to your questions:

Is there another way of specifying local_options on associations that I may have missed?

No other way that I can think of. I'm not sure how else to solve your problem more elegantly with current api. Although if you have some thoughts on augmenting association in such a way that would allow developers to add additional data to association's local_options more elegantly, I'd appreciate it if you'd share them.

I noticed that apart from the extractor, the differences between ::association and ::field is the option association: true. This option seems to be used in Blueprinter::BaseHelpers#associations, but I don't see where this helper is used. Is it still required?

You're right, it does not seem to be in use anymore and can be removed.