Reflections methods on ActiveRecord relations, for serialization

active_records_association_reflexion.rb

###
# Rails : 5.0.0
# Ruby : 2.3.0
#
# Reflections methods on ActiveRecord relations, for serialization
# purpose, for example.
#
# I used this to have some Hypermedia document when responding in JSON,
# with this informations, I could easily guess the _embedded links
# of my resources.


##
# Give an array of informations about each belongs_to associations
# of the ActiveRecord given.
#
# If the class given isn't an ActiveRecord, will return an empty array.
#
#
# Example of return
# ```
# class Contact < ActiveRecord::Base
#   belongs_to :user
# end
#
#
# > relation_infos(Contact, :belongs_to)
# [
#   {
#     association_name: :user,
#     association_klass_name: "User",
#     association_klass: User,
#     foreign_key: "user_id"
#   }
# ]
# ```
def relation_infos(model_klass, relation_type)
  relations = []
  return relations unless
    ['has_one',
     'belongs_to',
     'has_many'].include?(relation_type.to_s.downcase) &&
    model_klass.respond_to?(:reflect_on_all_associations)

  model_klass.reflect_on_all_associations(relation_type)\
             .collect do |association|
    association_name = association.name
    # Get the default association name, or the specified one in options hash.
    if association.options.key?(:class_name)
      klass_name = association.options[:class_name]
    else
      klass_name = association_name.to_s.singularize.camelize
    end
    klass = klass_name.to_s.constantize

    # Get the default foreign key, or the specified one in options hash.
    if association.options.key?(:foreign_key)
      foreign_key = association.options[:foreign_key]
    else
      foreign_key = "#{klass.table_name.singularize}_id"
    end

    return {
      association_name: association_name,
      association_klass_name: klass_name,
      association_klass: klass,
      foreign_key: foreign_key
    }
  end
end


# Examples 
# ========

def belongs_to_infos(model_klass)
  relation_infos(model_klass, :belongs_to)
end

def has_one_infos(model_klass)
  relation_infos(model_klass, :has_one)
end

def has_many_infos(model_klass)
  relation_infos(model_klass, :has_many)
end
puts 'Belongs to relations for User'
belongs_to_infos(User)
puts 'Has one relations for User'
has_one_infos(User)
puts 'Has many relations for User'
has_many_infos(User)