1 files changed, 53 insertions, 47 deletions

diff --git a/activerecord/lib/active_record/associations/builder/association.rb b/activerecord/lib/active_record/associations/builder/association.rb
index bbc1c20f60..1059fc032d 100644
--- a/activerecord/lib/active_record/associations/builder/association.rb
+++ b/activerecord/lib/active_record/associations/builder/association.rb
@@ -2,7 +2,7 @@
 # used by all associations.
 #
 # The hierarchy is defined as follows:
-#  Association 
+#  Association
 #    - SingularAssociation
 #      - BelongsToAssociation
 #      - HasOneAssociation
@@ -13,50 +13,44 @@
 module ActiveRecord::Associations::Builder
   class Association #:nodoc:
     class << self
-      attr_accessor :valid_options
+      attr_accessor :extensions
     end
+    self.extensions = []
 
-    self.valid_options = [:class_name, :foreign_key, :validate]
+    VALID_OPTIONS = [:class_name, :class, :foreign_key, :validate]
 
-    attr_reader :model, :name, :scope, :options, :reflection
+    attr_reader :name, :scope, :options
 
-    def self.build(*args, &block)
-      new(*args, &block).build
-    end
-
-    def initialize(model, name, scope, options)
+    def self.build(model, name, scope, options, &block)
       raise ArgumentError, "association names must be a Symbol" unless name.kind_of?(Symbol)
 
-      @model   = model
-      @name    = name
-
       if scope.is_a?(Hash)
-        @scope   = nil
-        @options = scope
-      else
-        @scope   = scope
-        @options = options
+        options = scope
+        scope   = nil
       end
 
-      if @scope && @scope.arity == 0
-        prev_scope = @scope
-        @scope = proc { instance_exec(&prev_scope) }
-      end
-    end
-
-    def mixin
-      @model.generated_feature_methods
+      builder = new(name, scope, options, &block)
+      reflection = builder.build(model)
+      builder.define_accessors model
+      builder.define_callbacks model, reflection
+      builder.define_extensions model
+      reflection
     end
 
-    include Module.new { def build; end }
+    def initialize(name, scope, options)
+      @name    = name
+      @scope   = scope
+      @options = options
 
-    def build
       validate_options
-      define_accessors
-      configure_dependency if options[:dependent]
-      @reflection = model.create_reflection(macro, name, scope, options, model)
-      super # provides an extension point
-      @reflection
+
+      if scope && scope.arity == 0
+        @scope = proc { instance_exec(&scope) }
+      end
+    end
+
+    def build(model)
+      ActiveRecord::Reflection.create(macro, name, scope, options, model)
     end
 
     def macro
@@ -64,26 +58,37 @@ module ActiveRecord::Associations::Builder
     end
 
     def valid_options
-      Association.valid_options
+      VALID_OPTIONS + Association.extensions.flat_map(&:valid_options)
     end
 
     def validate_options
       options.assert_valid_keys(valid_options)
     end
-    
+
+    def define_extensions(model)
+    end
+
+    def define_callbacks(model, reflection)
+      add_before_destroy_callbacks(model, name) if options[:dependent]
+      Association.extensions.each do |extension|
+        extension.build model, reflection
+      end
+    end
+
     # Defines the setter and getter methods for the association
     # class Post < ActiveRecord::Base
     #   has_many :comments
     # end
-    # 
+    #
     # Post.first.comments and Post.first.comments= methods are defined by this method...
 
-    def define_accessors
-      define_readers
-      define_writers
+    def define_accessors(model)
+      mixin = model.generated_feature_methods
+      define_readers(mixin)
+      define_writers(mixin)
     end
 
-    def define_readers
+    def define_readers(mixin)
       mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
         def #{name}(*args)
           association(:#{name}).reader(*args)
@@ -91,7 +96,7 @@ module ActiveRecord::Associations::Builder
       CODE
     end
 
-    def define_writers
+    def define_writers(mixin)
       mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
         def #{name}=(value)
           association(:#{name}).writer(value)
@@ -99,17 +104,18 @@ module ActiveRecord::Associations::Builder
       CODE
     end
 
-    def configure_dependency
+    def valid_dependent_options
+      raise NotImplementedError
+    end
+
+    private
+
+    def add_before_destroy_callbacks(model, name)
       unless valid_dependent_options.include? options[:dependent]
         raise ArgumentError, "The :dependent option must be one of #{valid_dependent_options}, but is :#{options[:dependent]}"
       end
 
-      n = name
-      model.before_destroy lambda { |o| o.association(n).handle_dependency }
-    end
-
-    def valid_dependent_options
-      raise NotImplementedError
+      model.before_destroy lambda { |o| o.association(name).handle_dependency }
     end
   end
 end