ReferenceField now store ObjectId's by default rather than DBRef (#290)

tests/migration/refrencefield_dbref_to_object_id.py

@@ -0,0 +1,52 @@
+# -*- coding: utf-8 -*-
+import unittest
+
+from mongoengine import Document, connect
+from mongoengine.connection import get_db
+from mongoengine.fields import StringField, ReferenceField, ListField
+
+__all__ = ('ConvertToObjectIdsModel', )
+
+
+class ConvertToObjectIdsModel(unittest.TestCase):
+
+    def setUp(self):
+        connect(db='mongoenginetest')
+        self.db = get_db()
+
+    def test_how_to_convert_to_object_id_reference_fields(self):
+        """Demonstrates migrating from 0.7 to 0.8
+        """
+
+        # 1. Old definition - using dbrefs
+        class Person(Document):
+            name = StringField()
+            parent = ReferenceField('self', dbref=True)
+            friends = ListField(ReferenceField('self', dbref=True))
+
+        Person.drop_collection()
+
+        p1 = Person(name="Wilson", parent=None).save()
+        f1 = Person(name="John", parent=None).save()
+        f2 = Person(name="Paul", parent=None).save()
+        f3 = Person(name="George", parent=None).save()
+        f4 = Person(name="Ringo", parent=None).save()
+        Person(name="Wilson Jr", parent=p1, friends=[f1, f2, f3, f4]).save()
+
+        # 2. Start the migration by changing the schema
+        # Change ReferenceField as now dbref defaults to False
+        class Person(Document):
+            name = StringField()
+            parent = ReferenceField('self')
+            friends = ListField(ReferenceField('self'))
+
+        # 3. Loop all the objects and mark parent as changed
+        for p in Person.objects:
+            p._mark_as_changed('parent')
+            p._mark_as_changed('friends')
+            p.save()
+
+        # 4. Confirmation of the fix!
+        wilson = Person.objects(name="Wilson Jr").as_pymongo()[0]
+        self.assertEqual(p1.id, wilson['parent'])
+        self.assertEqual([f1.id, f2.id, f3.id, f4.id], wilson['friends'])