Setup the allowed writer method in Model#finalize

* This is superior to memoizing the value because Model#finalize should only
  be called when the model has all the properties/methods added to it.
* Models must be finalize before instances being used. This was always always
  the contract, however the specs never enforced that. Now that this change
  is applied Model#finalize *must* be performed before using the initialized
  objects. Fixed the specs to comply with this.

lib/dm-core/model.rb

@@ -135,6 +135,7 @@ def raise_on_save_failure=(raise_on_save_failure)
     # @api public
     def finalize
       finalize_relationships
+      finalize_allowed_writer_methods
       assert_valid_name
       assert_valid_properties
       assert_valid_key
@@ -642,6 +643,13 @@ def load(records, query)
     # @api semipublic
     attr_reader :base_model
 
+    # The list of writer methods that can be mass-assigned to in #attributes=
+    #
+    # @return [Set]
+    #
+    # @api private
+    attr_reader :allowed_writer_methods
+
     # @api semipublic
     def default_repository_name
       Repository.default_name
@@ -701,19 +709,6 @@ def repositories
       [ repository ].to_set + @properties.keys.map { |repository_name| DataMapper.repository(repository_name) }
     end
 
-    # The list of writer methods that can be mass-assigned to in #attributes=
-    #
-    # @return [Set]
-    #
-    # @api private
-    def allowed_writer_methods
-      @allowed_writer_methods ||= begin
-        methods  = public_instance_methods.map { |method| method.to_s }.grep(WRITER_METHOD_REGEXP).to_set
-        methods -= INVALID_WRITER_METHODS
-        methods.freeze
-      end
-    end
-
     private
 
     # @api private
@@ -787,6 +782,17 @@ def finalize_relationships
       relationships(repository_name).each { |relationship| relationship.finalize }
     end
 
+    # Initialize the list of allowed writer methods
+    #
+    # @return [undefined]
+    #
+    # @api private
+    def finalize_allowed_writer_methods
+      @allowed_writer_methods  = public_instance_methods.map { |method| method.to_s }.grep(WRITER_METHOD_REGEXP).to_set
+      @allowed_writer_methods -= INVALID_WRITER_METHODS
+      @allowed_writer_methods.freeze
+    end
+
     # @api private
     # TODO: Remove this once appropriate warnings can be added.
     def assert_valid(force = false) # :nodoc:

spec/semipublic/associations/many_to_many_spec.rb

@@ -54,6 +54,8 @@ class WithDefaultCallable
     @article_model = Blog::Article
     @author_model  = Blog::Author
 
+    DataMapper.finalize
+
     n = @article_model.n
 
     @default_value          = [ @author_model.new(:name => 'Dan Kubb') ]

spec/semipublic/associations/many_to_one_spec.rb

@@ -23,6 +23,8 @@ class ::Comment
     @user_model    = User
     @comment_model = Comment
 
+    DataMapper.finalize
+
     @default_value          = @user_model.new(:name => 'dkubb', :age => 34, :description => 'Test')
     @default_value_callable = @user_model.new(:name => 'jdoe',  :age => 21, :description => 'Test')
 

spec/semipublic/associations/one_to_many_spec.rb

@@ -24,6 +24,8 @@ class Author
     @article_model = Blog::Article
     @author_model  = Blog::Author
 
+    DataMapper.finalize
+
     n = @article_model.n
 
     @default_value          = [ @author_model.new(:name => 'Dan Kubb') ]

spec/semipublic/associations/one_to_one_spec.rb

@@ -24,6 +24,8 @@ class Author
     @article_model = Blog::Article
     @author_model  = Blog::Author
 
+    DataMapper.finalize
+
     @default_value          = @author_model.new(:name => 'Dan Kubb')
     @default_value_callable = @author_model.new(:name => 'John Doe')