dynamic_matchers.rb

require "active_support/core_ext/regexp"

module ActiveRecord
  module DynamicMatchers #:nodoc:
    def respond_to_missing?(name, include_private = false)
      if self == Base
        super
      else
        match = Method.match(self, name)
        match && match.valid? || super
      end
    end

    private

      def method_missing(name, *arguments, &block)
        match = Method.match(self, name)

        if match && match.valid?
          match.define
          send(name, *arguments, &block)
        else
          super
        end
      end

      class Method
        @matchers = []

        class << self
          attr_reader :matchers

          def match(model, name)
            klass = matchers.find { |k| k.pattern.match?(name) }
            klass.new(model, name) if klass
          end

          def pattern
            @pattern ||= /\A#{prefix}_([_a-zA-Z]\w*)#{suffix}\Z/
          end

          def prefix
            raise NotImplementedError
          end

          def suffix
            ""
          end
        end

        attr_reader :model, :name, :attribute_names

        def initialize(model, name)
          @model           = model
          @name            = name.to_s
          @attribute_names = @name.match(self.class.pattern)[1].split("_and_")
          @attribute_names.map! { |n| @model.attribute_aliases[n] || n }
        end

        def valid?
          attribute_names.all? { |name| model.columns_hash[name] || model.reflect_on_aggregation(name.to_sym) }
        end

        def define
          model.class_eval <<-CODE, __FILE__, __LINE__ + 1
            def self.#{name}(#{signature})
              #{body}
            end
          CODE
        end

        private

          def body
            "#{finder}(#{attributes_hash})"
          end

        # The parameters in the signature may have reserved Ruby words, in order
        # to prevent errors, we start each param name with `_`.
          def signature
            attribute_names.map { |name| "_#{name}" }.join(", ")
          end

        # Given that the parameters starts with `_`, the finder needs to use the
        # same parameter name.
          def attributes_hash
            "{" + attribute_names.map { |name| ":#{name} => _#{name}" }.join(",") + "}"
          end

          def finder
            raise NotImplementedError
          end
      end

      class FindBy < Method
        Method.matchers << self

        def self.prefix
          "find_by"
        end

        def finder
          "find_by"
        end
      end

      class FindByBang < Method
        Method.matchers << self

        def self.prefix
          "find_by"
        end

        def self.suffix
          "!"
        end

        def finder
          "find_by!"
        end
      end
  end
end