Mongoengine官方文档中的介绍

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从官方文档可以看出MapField和DictField的区别仅限于MapField的类型必须与特定字段类型相匹配。

一个例子带你看清真相

def test_only_with_mapfields(self):

    class BlogPost(Document):
        content = StringField()
        author = MapField(field=StringField())

    BlogPost.drop_collection()

    post = BlogPost(content='Had a good coffee today...', 
                    author={'name': "Ross", "age": "20"}).save()

    obj = BlogPost.objects.only('author__name',).get()

    self.assertEquals(obj.author['name'], "Ross")
    self.assertEquals(obj.author.get("age", None), None)

代码来源:https://stackoverflow.com/questions/10679458/mongoengine-retriving-only-some-of-a-mapfield