Mongo delete_many方法不会从数据库中删除文档

根据 mongodb docs

db = Mongoid::Clients.default
collection = db[:oauth_access_tokens]
collection.delete_many({"resource_owner_id": "xxxxxxxxxxxxxx"})

根据我得到的结果,应该可以:

<Mongo::Operation::Result:58395820 documents=[{"ok"=>1, "n"=>0, "opTime"=>{"ts"=>#<BSON::Timestamp:0x00000006f62380 @seconds=1500457271, @increment=1>, "t"=>2}, "electionId"=>BSON::ObjectId('xxxxxxxxxxxxxxxxx')}]>

但是如果我在mongo shell中发现:

db.oauth_access_tokens.find({resource_owner_id: ObjectId("00000111111")})