Fix bugs \#444 and \#566 and \#577 which all had the same cause

This basically tries to make relationship initalization a bit smarter.
The code is pretty ugly, but it just tries loading up relations until
they work (that is, all related objects are loaded). This is done
for every Model#properties call, but of course cached once they are
in a sane state.

lib/dm-core/associations.rb

@@ -45,8 +45,8 @@ def many_to_one_relationships
     end
 
     def relationships(repository_name = default_repository_name)
-      @relationships ||= Hash.new { |h,k| h[k] = k == Repository.default_name ? {} : h[Repository.default_name].dup }
-      @relationships[repository_name]
+      @relationships ||= {}
+      @relationships[repository_name] ||= repository_name == Repository.default_name ? {} : relationships(Repository.default_name).dup
     end
 
     def n
@@ -145,6 +145,7 @@ def has(cardinality, name, options = {})
     #
     # @api public
     def belongs_to(name, options={})
+      @_valid_relations = false
       relationship = ManyToOne.setup(name, self, options)
       # Please leave this in - I will release contextual serialization soon
       # which requires this -- guyvdb

lib/dm-core/model.rb

@@ -154,6 +154,7 @@ def property(name, type, options = {})
       create_property_setter(property)
 
       properties(repository_name)[property.name] = property
+      @_valid_relations = false
 
       # Add property to the other mappings as well if this is for the default
       # repository.
@@ -195,6 +196,20 @@ def repositories
     end
 
     def properties(repository_name = default_repository_name)
+      # We need to check whether all relations are already set up.
+      # If this isn't the case, we try to reload them here
+      if !@_valid_relations && respond_to?(:many_to_one_relationships)
+        @_valid_relations = true
+        begin
+          many_to_one_relationships.each do |r|
+            r.child_key
+          end
+        rescue NameError
+          # Apparently not all relations are loaded,
+          # so we will try again later on
+          @_valid_relations = false
+        end
+      end
       @properties[repository_name] ||= repository_name == Repository.default_name ? PropertySet.new : properties(Repository.default_name).dup
     end
 

spec/integration/association_spec.rb

@@ -302,6 +302,18 @@ def self.default_repository_name
         area.should respond_to(:machine=)
       end
 
+      it 'should create the foreign key property immediately' do
+        class Duck
+          include DataMapper::Resource
+          property :id, Serial
+          belongs_to :sky
+        end
+        Duck.properties.slice(:sky_id).compact.should_not be_empty
+        duck = Duck.new
+        duck.should respond_to(:sky_id)
+        duck.should respond_to(:sky_id=)
+      end
+
       it 'should load without the parent'
 
       it 'should allow substituting the parent' do
@@ -331,7 +343,7 @@ class Ostrich
             end
           end
 
-          FlightlessBirds::Ostrich.properties.slice(:sky_id).should_not be_empty
+          FlightlessBirds::Ostrich.properties(ADAPTER).slice(:sky_id).compact.should_not be_empty
         end
       end