文档结构：
{ "_id": ObjectId("5d5e5de597eb2f0b70005d1a"), "userId": 1234, "word_records": [ { "word": "helloo", "from": "en", "to": "hi", "update_time": 1245748, "create_time": 235689 }, { "word": "xx", "from": "en", "to": "hi", "update_time": 1245748, "create_time": 235689 } ] }
一个用户想增加一个单词：
db.getCollection("collect_record").update({‘userId‘:1234},{$addToSet:{word_records:{‘word‘:‘update2‘,‘to‘:‘en‘,‘from‘:‘hi‘}}})
一个用户想删除一个单词：
db.getCollection("collect_record").update({"userId":123},{"$pull":{"word_records":{"word":"hello"}}})
分页查询某个用户的单词：
db.getCollection("collect_record").findOne({‘userId‘:123},{‘word_records‘:{$slice:[0,2]}})
原文：https://www.cnblogs.com/gaoquanquan/p/11399028.html