mongodb - mongodb是一一查找更新还是全部查找然后全部更新

Question

在mongodb中，更新多个文档的写操作不是原子的。如果有3条记录A，B，C需要更新。

MongoDB是否：

查找 A，更新 A，查找 B，更新 B，查找 C，更新 C

或者

找到A，B，C并保存到内存，forEach，更新A，B，C？

Answer 1

MongoDB 支持批量更新。

请看这个例子

db.mycollection.find()
{ "_id" : 1, "name" : "A", "designation" : "developer", "company" : "XYZ" }
{ "_id" : 2, "name" : "B", "designation" : "developer", "company" : "XYZ", "expe
rience" : 2 }
{ "_id" : 3, "name" : "C", "designation" : "developer", "company" : "XYZ", "expe
rience" : 3 }
{ "_id" : 4, "name" : "D", "designation" : "developer", "company" : "XYZ", "expe
rience" : 5 }
{ "_id" : 5, "name" : "E", "designation" : "Manager", "company" : "XYZ", "experi
ence" : 10 }
{ "_id" : 6, "name" : "F", "designation" : "Manager", "company" : "XYZ", "experi
ence" : 10 }
{ "_id" : 7, "name" : "G", "designation" : "Manager", "company" : "ABC", "experi
ence" : 10 }
{ "_id" : 8, "name" : "H", "designation" : "Developer", "company" : "ABC", "expe
rience" : 5 }
{ "_id" : 9, "name" : "I", "designation" : "Developer", "company" : "XYZ", "expe
rience" : 5 }

我将根据以下标准对 mycollection 进行批量更新

XYZ 公司将其成员是具有 5 年经验的开发人员提升为高级开发人员

我在 Mongo shell 中的命令是

var bulk = db.mycollection.initializeUnorderedBulkOp();

bulk.find({ $and:[{company:"XYZ"}, {experience:5}] }).update({$set:{designation:"
senior developer", comments:"Congrats you have been promoted to senior developer
"}});

bulk.execute();

Mongo Shell 执行查询后我们将得到以下结果

BulkWriteResult({
        "writeErrors" : [ ],
        "writeConcernErrors" : [ ],
        "nInserted" : 0,
        "nUpserted" : 0,
        "nMatched" : 2,
        "nModified" : 2,
        "nRemoved" : 0,
        "upserted" : [ ]
})

符合我们公司条件的两个文件：“XYZ”和经验：5，这些文件已更新（_id：4，_id：9）

db.mycollection.find()

{ "_id" : 1, "name" : "A", "designation" : "developer", "company" : "XYZ" }
{ "_id" : 2, "name" : "B", "designation" : "developer", "company" : "XYZ", "expe
rience" : 2 }
{ "_id" : 3, "name" : "C", "designation" : "developer", "company" : "XYZ", "expe
rience" : 3 }
{ "_id" : 4, "name" : "D", "designation" : "senior developer", "company" : "XYZ"
, "experience" : 5, "comments" : "Congrats you have been promoted to senior deve
loper" }
{ "_id" : 5, "name" : "E", "designation" : "Manager", "company" : "XYZ", "experi
ence" : 10 }
{ "_id" : 6, "name" : "F", "designation" : "Manager", "company" : "XYZ", "experi
ence" : 10 }
{ "_id" : 7, "name" : "G", "designation" : "Manager", "company" : "ABC", "experi
ence" : 10 }
{ "_id" : 8, "name" : "H", "designation" : "Developer", "company" : "ABC", "expe
rience" : 5 }
{ "_id" : 9, "name" : "I", "designation" : "senior developer", "company" : "XYZ"
, "experience" : 5, "comments" : "Congrats you have been promoted to senior deve
loper" }

其他相关的有趣参考：

MongoDB 中的 findAndModify 和 update 有什么区别？

https://docs.mongodb.com/manual/reference/method/Bulk.find.update/

https://docs.mongodb.com/manual/reference/method/db.collection.findAndModify/

https://docs.mongodb.com/v3.2/reference/method/db.collection.findOneAndUpdate/

希望能帮助到你！！