Initialize relationships before checking for keys

DataMapper.finalize now initializes all relationships before checking
for keys.  This allows a join model which consists entirely of
belongs_to relationships with `:key => true' to be considered valid.

[#1313 state:resolved]

lib/dm-core.rb

@@ -327,15 +327,15 @@ def self.finalize_model(model)
       raise IncompleteModelError, "#{name} must have at least one property or many to one relationship to be valid"
     end
 
-    if model.key(repository_name).empty?
-      raise IncompleteModelError, "#{name} must have a key to be valid"
-    end
-
     # initialize join models and target keys
     relationships.each do |relationship|
       relationship.child_key
       relationship.through if relationship.respond_to?(:through)
       relationship.via     if relationship.respond_to?(:via)
     end
+
+    if model.key(repository_name).empty?
+      raise IncompleteModelError, "#{name} must have a key to be valid"
+    end
   end
 end

spec/public/finalize_spec.rb

@@ -17,6 +17,25 @@ class ::ValidObject
       end
     end
 
+    it "should not raise on valid child model" do
+      class ::ValidChild
+        include DataMapper::Resource
+        belongs_to :valid_object, :key => true
+      end
+      class ::ValidObject
+        include DataMapper::Resource
+        property :id, Integer, :key => true
+      end
+      begin
+        method(:subject).should_not raise_error
+      ensure
+        DataMapper::Model.descendants.delete(ValidChild)
+        DataMapper::Model.descendants.delete(ValidObject)
+        Object.send(:remove_const, :ValidChild)
+        Object.send(:remove_const, :ValidObject)
+      end
+    end
+
     it 'should raise on an anonymous model' do
       model = Class.new do
         include DataMapper::Resource