Refactor auto migration into two steps

lib/dm-core/associations.rb

@@ -40,6 +40,7 @@ class UnsavedParentError < RuntimeError
     #
     # @api private
     def many_to_one_relationships
+      relationships unless @relationships # needs to be initialized!
       @relationships.values.collect do |rels| rels.values end.flatten.select do |relationship| relationship.child_model == self end
     end
 

lib/dm-core/auto_migrations.rb

@@ -8,9 +8,14 @@ class AutoMigrator
     #
     # @param Symbol repository_name the repository to be migrated
     # @calls DataMapper::Resource#auto_migrate!
-    def self.auto_migrate(repository_name = nil)
-      DataMapper::Resource.descendants.each do |model|
-        model.auto_migrate!(repository_name)
+    def self.auto_migrate(repository_name = nil, *descendants)
+      descendants = DataMapper::Resource.descendants.to_a if descendants.empty?
+      descendants.reverse.each do |model|
+        model.auto_migrate_down!(repository_name)
+      end
+
+      descendants.each do |model|
+        model.auto_migrate_up!(repository_name)
       end
     end
 
@@ -34,11 +39,35 @@ module AutoMigrations
     #
     # @param Symbol repository_name the repository to be migrated
     def auto_migrate!(repository_name = nil)
+      auto_migrate_down!(repository_name)
+      auto_migrate_up!(repository_name)
+    end
+
+    ##
+    # Destructively migrates the data-store down, which basically
+    # deletes all the models.
+    # REPEAT: THIS IS DESTRUCTIVE
+    #
+    # @param Symbol repository_name the repository to be migrated
+    def auto_migrate_down!(repository_name = nil)
       if self.superclass != Object
         self.superclass.auto_migrate!(repository_name)
       else
         repository(repository_name) do |r|
           r.adapter.destroy_model_storage(r, self)
+        end
+      end
+    end
+
+    ##
+    # Auto migrates the data-store to match the model
+    #
+    # @param Symbol repository_name the repository to be migrated
+    def auto_migrate_up!(repository_name = nil)
+      if self.superclass != Object
+        self.superclass.auto_migrate!(repository_name)
+      else
+        repository(repository_name) do |r|
           r.adapter.create_model_storage(r, self)
         end
       end

spec/integration/association_spec.rb

@@ -370,6 +370,13 @@ class Ostrich
         Machine.first(:name => 'machine10').should_not be_nil
       end
 
+      it 'should set and retrieve associations on not yet saved objects' do
+        e = Machine.create(:name => 'machine10')
+        y = e.areas.build(:name => 'area10')
+
+        y.machine.name.should == 'machine10'
+      end
+
       it 'should convert NULL parent ids into nils' do
         Area.first(:name => 'area2').machine.should be_nil
       end

spec/unit/auto_migrations_spec.rb

@@ -85,7 +85,8 @@
 
       models.each do |model|
         DataMapper::Resource.descendants << model
-        model.should_receive(:auto_migrate!).with(@repository_name)
+        model.should_receive(:auto_migrate_down!).with(@repository_name)
+        model.should_receive(:auto_migrate_up!).with(@repository_name)
       end
 
       DataMapper::AutoMigrator.auto_migrate(@repository_name)