association.rb

module ActiveRecord::Associations::Builder
  class Association #:nodoc:
    class << self
      attr_accessor :valid_options
    end

    self.valid_options = [:class_name, :foreign_key, :validate]

    attr_reader :model, :name, :scope, :options, :reflection

    def self.build(*args, &block)
      new(*args, &block).build
    end

    def initialize(model, name, scope, options)
      @model   = model
      @name    = name

      if scope.is_a?(Hash)
        @scope   = nil
        @options = scope
      else
        @scope   = scope
        @options = options
      end

      if @scope && @scope.arity == 0
        prev_scope = @scope
        @scope = proc { instance_exec(&prev_scope) }
      end
    end

    def mixin
      @model.generated_feature_methods
    end

    include Module.new { def build; end }

    def build
      validate_options
      define_accessors
      @reflection = model.create_reflection(macro, name, scope, options, model)
      super # provides an extension point
      @reflection
    end

    def macro
      raise NotImplementedError
    end

    def valid_options
      Association.valid_options
    end

    def validate_options
      options.assert_valid_keys(valid_options)
    end

    def define_accessors
      define_readers
      define_writers
    end

    def define_readers
      name = self.name
      mixin.redefine_method(name) do |*params|
        association(name).reader(*params)
      end
    end

    def define_writers
      name = self.name
      mixin.redefine_method("#{name}=") do |value|
        association(name).writer(value)
      end
    end

    def validate_dependent_option(valid_options)
      unless valid_options.include? options[:dependent]
        raise ArgumentError, "The :dependent option must be one of #{valid_options}, but is :#{options[:dependent]}"
      end

      if options[:dependent] == :restrict
        ActiveSupport::Deprecation.warn(
          "The :restrict option is deprecated. Please use :restrict_with_exception instead, which " \
          "provides the same functionality."
        )
      end
    end
  end
end