Add a changelog entry [ci skip]

`BaseDocument.to_dict` serializes a document/embedded document into a dict,
which can be easily consumed by other modules (which in this case don't need
to be aware of MongoEngine-specific object types).

The output dict contains key-value pairs where:
* Keys are field names as they're defined on the document (as opposed to e.g.
  how they're stored in MongoDB).
* Values are field values in their deserialized form (i.e. the same form that
  you get when you access `doc.some_field_name`).

docs/changelog.rst

@@ -6,6 +6,7 @@ Changelog
 Development
 ===========
 - (Fill this out as you fix issues and develop your features).
+- Add a `BaseDocument.to_dict` method #2101
 
 Changes in 0.18.1
 =================

mongoengine/base/document.py

@@ -309,9 +309,7 @@ class BaseDocument(object):
         return self._data['_text_score']
 
     def to_mongo(self, use_db_field=True, fields=None):
-        """
-        Return as SON data ready for use with MongoDB.
-        """
+        """Return as SON data ready for use with MongoDB."""
         fields = fields or []
 
         data = SON()
@@ -412,12 +410,35 @@ class BaseDocument(object):
             message = 'ValidationError (%s:%s) ' % (self._class_name, pk)
             raise ValidationError(message, errors=errors)
 
+    def to_dict(self):
+        """Serialize this document into a dict.
+
+        Return field names as they're defined on the document (as opposed to
+        e.g. how they're stored in MongoDB). Return values in their
+        deserialized form (i.e. the same form that you get when you access
+        `doc.some_field_name`). Serialize embedded documents recursively.
+
+        The resultant dict can be consumed easily by other modules which
+        don't need to be aware of MongoEngine-specific object types.
+
+        :return dict: dictionary of field name & value pairs.
+        """
+        data_dict = {}
+        for field_name in self._fields:
+            value = getattr(self, field_name)
+            if isinstance(value, BaseDocument):
+                data_dict[field_name] = value.to_dict()
+            else:
+                data_dict[field_name] = value
+        return data_dict
+
     def to_json(self, *args, **kwargs):
         """Convert this document to JSON.
 
         :param use_db_field: Serialize field names as they appear in
             MongoDB (as opposed to attribute names on this document).
             Defaults to True.
+        :return str: string representing the jsonified document.
         """
         use_db_field = kwargs.pop('use_db_field', True)
         return json_util.dumps(self.to_mongo(use_db_field), *args, **kwargs)
@@ -426,12 +447,13 @@ class BaseDocument(object):
     def from_json(cls, json_data, created=False):
         """Converts json data to a Document instance
 
-        :param json_data: The json data to load into the Document
-        :param created: If True, the document will be considered as a brand new document
-                        If False and an id is provided, it will consider that the data being
-                        loaded corresponds to what's already in the database (This has an impact of subsequent call to .save())
-                        If False and no id is provided, it will consider the data as a new document
-                        (default ``False``)
+        :param str json_data: The json data to load into the Document
+        :param bool created: If True, the document will be considered as
+            a brand new document. If False and an ID is provided, it will
+            consider that the data being loaded corresponds to what's already
+            in the database (This has an impact of subsequent call to .save())
+            If False and no id is provided, it will consider the data as a new
+            document (default ``False``)
         """
         return cls._from_son(json_util.loads(json_data), created=created)
 

tests/document/instance.py

@@ -3525,5 +3525,76 @@ class InstanceTest(MongoDBTestCase):
             User.objects().select_related()
 
 
+class DocumentToDictTest(MongoDBTestCase):
+    """Class for testing the BaseDocument.to_dict method."""
+
+    def test_to_dict(self):
+        class Person(Document):
+            name = StringField()
+            age = IntField()
+
+        p = Person(name='Tom', age=30)
+        self.assertEqual(p.to_dict(), {'id': None, 'name': 'Tom', 'age': 30})
+
+    def test_to_dict_with_a_persisted_doc(self):
+        class Person(Document):
+            name = StringField()
+            age = IntField()
+
+        p = Person.objects.create(name='Tom', age=30)
+        p_dict = p.to_dict()
+        self.assertTrue(p_dict['id'])
+        self.assertEqual(p_dict['name'], 'Tom')
+        self.assertEqual(p_dict['age'], 30)
+
+    def test_to_dict_empty_doc(self):
+        class Person(Document):
+            name = StringField()
+            age = IntField()
+
+        p = Person()
+        self.assertEqual(p.to_dict(), {'id': None, 'name': None, 'age': None})
+
+    def test_to_dict_with_default_values(self):
+        class Person(Document):
+            name = StringField(default='Unknown')
+            age = IntField(default=0)
+
+        p = Person()
+        self.assertEqual(
+            p.to_dict(),
+            {'id': None, 'name': 'Unknown', 'age': 0}
+        )
+
+    def test_to_dict_with_a_db_field(self):
+        class Person(Document):
+            name = StringField(db_field='db_name')
+
+        p = Person(name='Tom')
+        self.assertEqual(p.to_dict(), {'id': None, 'name': 'Tom'})
+
+    def test_to_dict_with_a_primary_key(self):
+        class Person(Document):
+            username = StringField(primary_key=True)
+
+        p = Person(username='tomtom')
+        self.assertEqual(p.to_dict(), {'username': 'tomtom'})
+
+    def test_to_dict_with_an_embedded_document(self):
+        class Book(EmbeddedDocument):
+            title = StringField()
+
+        class Author(Document):
+            name = StringField()
+            book = EmbeddedDocumentField(Book)
+
+        a = Author(name='Yuval', book=Book(title='Sapiens'))
+        self.assertEqual(a.to_dict(), {
+            'id': None,
+            'name': 'Yuval',
+            'book': {'title': 'Sapiens'}
+        })
+
+
 if __name__ == '__main__':
     unittest.main()