mongodb是一一查找更新还是全部查找然后全部更新答案

【问题标题】：Does mongodb find and update one by one or find all then update allmongodb是一一查找更新还是全部查找然后全部更新
【发布时间】：2017-02-08 00:23:30
【问题描述】：

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:

查找 A，更新 A，查找 B，更新 B，查找 C，更新 C

或

找到 A,B,C 并保存到内存中，forEach，更新 A,B,C？

【问题讨论】：

标签： mongodb mongodb-update

【解决方案1】：

Bulk Update 在 MongoDB 中受支持。

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 }

我将根据以下条件对 mycollection 进行批量更新

XYZ 公司向他们的开发人员成员提供晋升有5年资深开发经验

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 执行查询后我们会得到以下结果

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档：“XYZ”和经验：5，并且这些文档已更新（_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" }

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/

希望对你有帮助！！

【讨论】：