added get_next_value to SequenceField

mongoengine/fields.py

@@ -1465,6 +1465,17 @@ class SequenceField(BaseField):
                                              upsert=True)
         return self.value_decorator(counter['next'])
 
+    def get_next_value(self):
+        sequence_name = self.get_sequence_name()
+        sequence_id = "%s.%s" % (sequence_name, self.name)
+        collection = get_db(alias=self.db_alias)[self.collection_name]
+        data = collection.find_one({"_id": sequence_id})
+
+        if data:
+            return data['next']
+
+        return 1
+
     def get_sequence_name(self):
         if self.sequence_name:
             return self.sequence_name

tests/fields/fields.py

@@ -1917,6 +1917,23 @@ class FieldTest(unittest.TestCase):
         c = self.db['mongoengine.counters'].find_one({'_id': 'person.id'})
         self.assertEqual(c['next'], 1000)
 
+
+    def test_sequence_field_get_next_value(self):
+        class Person(Document):
+            id = SequenceField(primary_key=True)
+            name = StringField()
+
+        self.db['mongoengine.counters'].drop()
+        Person.drop_collection()
+
+        for x in xrange(10):
+            Person(name="Person %s" % x).save()
+
+        self.assertEqual(Person.id.get_next_value(), 10)
+        self.db['mongoengine.counters'].drop()
+
+        self.assertEqual(Person.id.get_next_value(), 1)
+        
     def test_sequence_field_sequence_name(self):
         class Person(Document):
             id = SequenceField(primary_key=True, sequence_name='jelly')