当我使用aiomotoregine的唯一属性时，总是抛出

Question

我正在为Mongo ORM使用aiomotorengine，但是当我为字段设置唯一属性时，我总是得到pymongo.errors.OperationFailure的错误

class User(Document):
    __collection__ = 'users'

    name = StringField(default='nick',unique =True)
    age = IntField(default=1)

connect('test',io_loop=loop,port=27017,host = 'localhost')

pymongo.errors.OperationFailure: The field 'alias' is not valid for an index specification. Specification: { key: { name: 1 }, unique: true, alias: null, name: "name_1" }