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@@ -349,6 +349,27 @@ module ActiveRecord
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     end
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   end
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+  # MigrationProxy is used to defer loading of the actual migration classes
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+  # until they are needed
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+  class MigrationProxy
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+
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+    attr_accessor :name, :version, :filename
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+
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+    delegate :migrate, :announce, :write, :to=>:migration
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+
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+    private
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+
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+      def migration
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+        @migration ||= load_migration
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+      end
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+
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+      def load_migration
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+        load(filename)
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+        name.constantize
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+      end
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+
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+  end
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+
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   class Migrator#:nodoc:
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     class << self
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       def migrate(migrations_path, target_version = nil)
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@@ -437,7 +458,7 @@ module ActiveRecord
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       runnable.pop if down? && !target.nil?
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       runnable.each do |migration|
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-        Base.logger.info "Migrating to #{migration} (#{migration.version})"
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+        Base.logger.info "Migrating to #{migration.name} (#{migration.version})"
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         # On our way up, we skip migrating the ones we've already migrated
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         # On our way down, we skip reverting the ones we've never migrated
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@@ -470,11 +491,10 @@ module ActiveRecord
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             raise DuplicateMigrationNameError.new(name.camelize) 
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           end
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-          load(file)
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-          
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-          klasses << returning(name.camelize.constantize) do |klass|
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-            class << klass; attr_accessor :version end
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-            klass.version = version
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+          klasses << returning(MigrationProxy.new) do |migration|
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+            migration.name     = name.camelize
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+            migration.version  = version
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+            migration.filename = file
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           end
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         end
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@@ -922,6 +922,26 @@ if ActiveRecord::Base.connection.supports_migrations?
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       migrations[0].name    == 'innocent_jointable'
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     end
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+    def test_only_loads_pending_migrations
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+      # migrate up to 1
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+      ActiveRecord::Migrator.up(MIGRATIONS_ROOT + "/valid", 1)
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+
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+      # now unload the migrations that have been defined
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+      PeopleHaveLastNames.unloadable
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+      ActiveSupport::Dependencies.remove_unloadable_constants!
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+
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+      ActiveRecord::Migrator.migrate(MIGRATIONS_ROOT + "/valid", nil)
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+
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+      assert !defined? PeopleHaveLastNames
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+
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+      %w(WeNeedReminders, InnocentJointable).each do |migration|
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+        assert defined? migration
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+      end
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+
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+    ensure
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+      load(MIGRATIONS_ROOT + "/valid/1_people_have_last_names.rb")
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+    end
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+
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     def test_migrator_interleaved_migrations
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       ActiveRecord::Migrator.up(MIGRATIONS_ROOT + "/interleaved/pass_1")
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