Extract generic attribute method generation to AMo

2 files changed, 268 insertions, 0 deletions

diff --git a/activemodel/lib/active_model.rb b/activemodel/lib/active_model.rb
index 2de19597b1..9bb4cf8b54 100644
--- a/activemodel/lib/active_model.rb
+++ b/activemodel/lib/active_model.rb
@@ -26,6 +26,7 @@ $:.unshift(activesupport_path) if File.directory?(activesupport_path)
 require 'active_support'
 
 module ActiveModel
+  autoload :AttributeMethods, 'active_model/attribute_methods'
   autoload :Conversion, 'active_model/conversion'
   autoload :DeprecatedErrorMethods, 'active_model/deprecated_error_methods'
   autoload :Errors, 'active_model/errors'
diff --git a/activemodel/lib/active_model/attribute_methods.rb b/activemodel/lib/active_model/attribute_methods.rb
new file mode 100644
index 0000000000..de80559036
--- /dev/null
+++ b/activemodel/lib/active_model/attribute_methods.rb
@@ -0,0 +1,267 @@
+module ActiveModel
+  class MissingAttributeError < NoMethodError
+  end
+
+  module AttributeMethods
+    extend ActiveSupport::Concern
+
+    # Declare and check for suffixed attribute methods.
+    module ClassMethods
+      # Defines an "attribute" method (like +inheritance_column+ or
+      # +table_name+). A new (class) method will be created with the
+      # given name. If a value is specified, the new method will
+      # return that value (as a string). Otherwise, the given block
+      # will be used to compute the value of the method.
+      #
+      # The original method will be aliased, with the new name being
+      # prefixed with "original_". This allows the new method to
+      # access the original value.
+      #
+      # Example:
+      #
+      #   class A < ActiveRecord::Base
+      #     define_attr_method :primary_key, "sysid"
+      #     define_attr_method( :inheritance_column ) do
+      #       original_inheritance_column + "_id"
+      #     end
+      #   end
+      def define_attr_method(name, value=nil, &block)
+        sing = metaclass
+        sing.send :alias_method, "original_#{name}", name
+        if block_given?
+          sing.send :define_method, name, &block
+        else
+          # use eval instead of a block to work around a memory leak in dev
+          # mode in fcgi
+          sing.class_eval "def #{name}; #{value.to_s.inspect}; end"
+        end
+      end
+
+      # Declares a method available for all attributes with the given prefix.
+      # Uses +method_missing+ and <tt>respond_to?</tt> to rewrite the method.
+      #
+      #   #{prefix}#{attr}(*args, &block)
+      #
+      # to
+      #
+      #   #{prefix}attribute(#{attr}, *args, &block)
+      #
+      # An <tt>#{prefix}attribute</tt> instance method must exist and accept at least
+      # the +attr+ argument.
+      #
+      # For example:
+      #
+      #   class Person < ActiveRecord::Base
+      #     attribute_method_prefix 'clear_'
+      #
+      #     private
+      #       def clear_attribute(attr)
+      #         ...
+      #       end
+      #   end
+      #
+      #   person = Person.find(1)
+      #   person.name          # => 'Gem'
+      #   person.clear_name
+      #   person.name          # => ''
+      def attribute_method_prefix(*prefixes)
+        attribute_method_matchers.concat(prefixes.map { |prefix| AttributeMethodMatcher.new :prefix => prefix })
+        undefine_attribute_methods
+      end
+
+      # Declares a method available for all attributes with the given suffix.
+      # Uses +method_missing+ and <tt>respond_to?</tt> to rewrite the method.
+      #
+      #   #{attr}#{suffix}(*args, &block)
+      #
+      # to
+      #
+      #   attribute#{suffix}(#{attr}, *args, &block)
+      #
+      # An <tt>attribute#{suffix}</tt> instance method must exist and accept at least
+      # the +attr+ argument.
+      #
+      # For example:
+      #
+      #   class Person < ActiveRecord::Base
+      #     attribute_method_suffix '_short?'
+      #
+      #     private
+      #       def attribute_short?(attr)
+      #         ...
+      #       end
+      #   end
+      #
+      #   person = Person.find(1)
+      #   person.name           # => 'Gem'
+      #   person.name_short?    # => true
+      def attribute_method_suffix(*suffixes)
+        attribute_method_matchers.concat(suffixes.map { |suffix| AttributeMethodMatcher.new :suffix => suffix })
+        undefine_attribute_methods
+      end
+
+      # Declares a method available for all attributes with the given prefix
+      # and suffix. Uses +method_missing+ and <tt>respond_to?</tt> to rewrite
+      # the method.
+      #
+      #   #{prefix}#{attr}#{suffix}(*args, &block)
+      #
+      # to
+      #
+      #   #{prefix}attribute#{suffix}(#{attr}, *args, &block)
+      #
+      # An <tt>#{prefix}attribute#{suffix}</tt> instance method must exist and
+      # accept at least the +attr+ argument.
+      #
+      # For example:
+      #
+      #   class Person < ActiveRecord::Base
+      #     attribute_method_affix :prefix => 'reset_', :suffix => '_to_default!'
+      #
+      #     private
+      #       def reset_attribute_to_default!(attr)
+      #         ...
+      #       end
+      #   end
+      #
+      #   person = Person.find(1)
+      #   person.name                         # => 'Gem'
+      #   person.reset_name_to_default!
+      #   person.name                         # => 'Gemma'
+      def attribute_method_affix(*affixes)
+        attribute_method_matchers.concat(affixes.map { |affix| AttributeMethodMatcher.new :prefix => affix[:prefix], :suffix => affix[:suffix] })
+        undefine_attribute_methods
+      end
+
+      def define_attribute_methods(attr_names)
+        return if attribute_methods_generated?
+        attr_names.each do |name|
+          attribute_method_matchers.each do |method|
+            method_name = "#{method.prefix}#{name}#{method.suffix}"
+            unless instance_method_already_implemented?(method_name)
+              generate_method = "define_method_#{method.prefix}attribute#{method.suffix}"
+
+              if respond_to?(generate_method)
+                send(generate_method, name)
+              else
+                generated_attribute_methods.module_eval("def #{method_name}(*args); send(:#{method.prefix}attribute#{method.suffix}, '#{name}', *args); end", __FILE__, __LINE__)
+              end
+            end
+          end
+        end
+      end
+
+      def undefine_attribute_methods
+        generated_attribute_methods.module_eval do
+          instance_methods.each { |m| undef_method(m) }
+        end
+        @attribute_methods_generated = nil
+      end
+
+      def generated_attribute_methods #:nodoc:
+        @generated_attribute_methods ||= begin
+          @attribute_methods_generated = true
+          mod = Module.new
+          include mod
+          mod
+        end
+      end
+
+      def attribute_methods_generated?
+        @attribute_methods_generated ? true : false
+      end
+
+      protected
+        def instance_method_already_implemented?(method_name)
+          method_defined?(method_name)
+        end
+
+      private
+        class AttributeMethodMatcher
+          attr_reader :prefix, :suffix
+
+          AttributeMethodMatch = Struct.new(:prefix, :base, :suffix)
+
+          def initialize(options = {})
+            options.symbolize_keys!
+            @prefix, @suffix = options[:prefix] || '', options[:suffix] || ''
+            @regex = /^(#{Regexp.escape(@prefix)})(.+?)(#{Regexp.escape(@suffix)})$/
+          end
+
+          def match(method_name)
+            if matchdata = @regex.match(method_name)
+              AttributeMethodMatch.new(matchdata[1], matchdata[2], matchdata[3])
+            else
+              nil
+            end
+          end
+        end
+
+        def attribute_method_matchers #:nodoc:
+          @@attribute_method_matchers ||= []
+        end
+    end
+
+    # Allows access to the object attributes, which are held in the <tt>@attributes</tt> hash, as though they
+    # were first-class methods. So a Person class with a name attribute can use Person#name and
+    # Person#name= and never directly use the attributes hash -- except for multiple assigns with
+    # ActiveRecord#attributes=. A Milestone class can also ask Milestone#completed? to test that
+    # the completed attribute is not +nil+ or 0.
+    #
+    # It's also possible to instantiate related objects, so a Client class belonging to the clients
+    # table with a +master_id+ foreign key can instantiate master through Client#master.
+    def method_missing(method_id, *args, &block)
+      method_name = method_id.to_s
+      if match = match_attribute_method?(method_name)
+        guard_private_attribute_method!(method_name, args)
+        return __send__("#{match.prefix}attribute#{match.suffix}", match.base, *args, &block)
+      end
+      super
+    end
+
+    # A Person object with a name attribute can ask <tt>person.respond_to?(:name)</tt>,
+    # <tt>person.respond_to?(:name=)</tt>, and <tt>person.respond_to?(:name?)</tt>
+    # which will all return +true+.
+    alias :respond_to_without_attributes? :respond_to?
+    def respond_to?(method, include_private_methods = false)
+      if super
+        return true
+      elsif !include_private_methods && super(method, true)
+        # If we're here then we haven't found among non-private methods
+        # but found among all methods. Which means that given method is private.
+        return false
+      elsif match_attribute_method?(method.to_s)
+        return true
+      end
+      super
+    end
+
+    protected
+      def attribute_method?(attr_name)
+        attributes.include?(attr_name)
+      end
+
+    private
+      # Returns a struct representing the matching attribute method.
+      # The struct's attributes are prefix, base and suffix.
+      def match_attribute_method?(method_name)
+        self.class.send(:attribute_method_matchers).each do |method|
+          if (match = method.match(method_name)) && attribute_method?(match.base)
+            return match
+          end
+        end
+        nil
+      end
+
+      # prevent method_missing from calling private methods with #send
+      def guard_private_attribute_method!(method_name, args)
+        if self.class.private_method_defined?(method_name)
+          raise NoMethodError.new("Attempt to call private method", method_name, args)
+        end
+      end
+
+      def missing_attribute(attr_name, stack)
+        raise ActiveModel::MissingAttributeError, "missing attribute: #{attr_name}", stack
+      end
+  end
+end