Ensure static attributes are executed before dynamic ones.

Static attributes must be executed first because dynamic attributes might
rely on them. This is really important when using the :parent relationship.

Previous code didn't work fine in situations like this one:
  Factory.define(:generic_user, :class => User) do |u|
    u.email { |user| "#{user.name}@example.com }
  end

  Factory.define(:flavio, :parent => :generic_user) do |u|
    u.name "flavio"
  end

When building a :user object the previous code would have set the email
attribute and then the name attribute. This results in a user object with
an invalid email address: the 'name' attribute is yet not set while the
'email' attribute is evaluated.

Closes #159

lib/factory_girl/attribute.rb

@@ -8,6 +8,7 @@ class AttributeDefinitionError < RuntimeError
   end
 
   class Attribute #:nodoc:
+    include Comparable
 
     attr_reader :name
 
@@ -28,6 +29,16 @@ def add_to(proxy)
     def association?
       false
     end
+
+    def priority
+      1
+    end
+
+    def <=>(another)
+      return nil unless another.is_a? Attribute
+      self.priority <=> another.priority
+    end
+
   end
 
 end

lib/factory_girl/attribute/static.rb

@@ -11,7 +11,10 @@ def initialize(name, value)
       def add_to(proxy)
         proxy.set(name, @value)
       end
-    end
 
+      def priority
+        0
+      end
+    end
   end
 end

lib/factory_girl/factory.rb

@@ -49,7 +49,9 @@ def inherit_from(parent) #:nodoc:
           new_attributes << attribute.clone
         end
       end
-      @attributes.unshift *new_attributes
+
+      @attributes += new_attributes
+      @attributes.sort!
     end
 
     def define_attribute(attribute)

spec/acceptance/parent_spec.rb

@@ -8,11 +8,11 @@
     FactoryGirl.define do
       factory :user do
         name  "John"
-        email "john@example.com"
+        email { "#{name.downcase}@example.com" }
 
         factory :admin do
+          name "admin"
           admin true
-          email "admin@example.com"
         end
 
         factory :guest do
@@ -28,16 +28,18 @@
     its(:email) { should == "john@example.com" }
   end
 
-  describe "the child class" do
+  describe "the child class redefining parent's static method used by a dynamic method" do
     subject     { FactoryGirl.create(:admin) }
     it          { should be_kind_of(User) }
     it          { should be_admin }
-    its(:name)  { should == "John" }
+    its(:name)  { should == "admin" }
     its(:email) { should == "admin@example.com" }
   end
 
-  describe "the child class with parent attribute" do
+  describe "the child class redefining parent's dynamic method" do
     subject     { FactoryGirl.create(:guest) }
+    it          { should_not be_admin }
+    its(:name)  { should == "John" }
     its(:email) { should eql "John-guest@example.com" }
   end
 end

spec/factory_girl/attribute_spec.rb

@@ -31,4 +31,13 @@
   it "should convert names to symbols" do
     FactoryGirl::Attribute.new('name').name.should == :name
   end
+
+  it "should return nil when is compared with a non-attribute object" do
+    (@attr <=> "foo").should == nil
+  end
+
+  it "should use priority to perform comparisons" do
+    attr2 = FactoryGirl::Attribute.new('name')
+    (@attr <=> attr2).should == 0
+  end
 end