MongoDB更改数据update和save方法

发布时间：2023-10-04 14:44:11 所属栏目：系统来源：

导读：前面我简单介绍了下MongoDB怎样插入数据.那么数据插入到数据库中,就可能会修改数据.在MongoDB中,它提供了修改数据的方法:update.下面,我来简单说下update的使用方法.

首先,我们操作的数据都存放在test数据库中的

前面我简单介绍了下MongoDB怎样插入数据.那么数据插入到数据库中,就可能会修改数据.在MongoDB中,它提供了修改数据的方法:update.下面,我来简单说下update的使用方法.

首先,我们操作的数据都存放在test数据库中的name集合,集合中有4条记录如下:

> db

test

> show collections

name

system.indexes

> db.name.find()

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "xiaoqiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "dengdeng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

下面我们来试着修改一下这些数据.在前面的插入中,我说过,插入时可以以文档的的方式插入,也可以先把文档赋值给变量,再以变量的方式插入.update方法也可以用这两种方式.我先用文档的方式来修改集合中的第二条记录,命令如下:

> db.name.update({"_id" : ObjectId("5059223a955cfb1fd75066cc")},{"fname" : "qiang", "lname" : "he"})

> db.name.find()    #检查发现,数据修改过来了,和预期的结果一样

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "dengdeng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

我们再用变量的方式来修改该集合中的第三条记录.首先将它找出来赋值给变量someone:

> someone=db.name.findOne({"_id" : ObjectId("50592245955cfb1fd75066cd")})

{

    "_id" : ObjectId("50592245955cfb1fd75066cd"),

    "fname" : "dengdeng",

    "lname" : "pan"

}

重新赋值你要修改的内容来修改变量someone的值:

> someone.fname="deng"

deng

用修改过的变量替换之前文档的位置来达到修改数据的目的:

> db.name.update({"_id" : ObjectId("50592245955cfb1fd75066cd")},someone)

> db.name.find()    #检查发现,数据修改过来了,和预期的结果一样

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

之前我说过,save函数实际就是根据参数条件,调用了insert或update函数.那么save方法是否也能实现数据的修改操作呢?下面我们来实验一下.首先还是以文档的方式来进行修改操作:

> db.name.save({"_id" : ObjectId("50592253955cfb1fd75066ce")}, {"fname" : "dongren", "lname" : "zeng"})

> db.name.find()    #检查发现,数据修改过来了,但和预期的结果不一样,跟之前插入数据一样,save方法也同样将第二个参数"忽略"了.

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce") }

正确的操作方式如下:

> db.name.save({"_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "dongren", "lname" : "zeng"})

> db.name.find()    #检查发现,数据修改过来了,和预期的结果一样

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "dongren", "lname" : "zeng" }

下面使用变量的方式来修改:

> someone=db.name.findOne({"_id" : ObjectId("50592253955cfb1fd75066ce")})

{

    "_id" : ObjectId("50592253955cfb1fd75066ce"),

    "fname" : "dongren",

    "lname" : "zeng"

}

> someone.fname="guage"

guage

> db.name.save(someone)

> db.name.find()    #检查发现,数据修改过来了,和预期的结果一样

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

下面,我们也同样来看看save和update这两方法的具体实现.首先是save方法:

> db.name.save

function (obj) {

    if (obj == null || typeof obj == "undefined") {

        throw "can't save a null";

    }

    if (typeof obj == "number" || typeof obj == "string") {

        throw "can't save a number or string";

    }

    if (typeof obj._id == "undefined") {

        obj._id = new ObjectId;

        return this.insert(obj);

    } else {

        return this.update({_id:obj._id}, obj, true);

    }

}

参数说明：

    obj：要更新的记录，只能是单条记录，如果collection没有存在与obj一样的id，则添加一条记录，否则更新.

再来看看update方法:

> db.name.update

function (query, obj, upsert, multi) {

    assert(query, "need a query");

    assert(obj, "need an object");

    var firstKey = null;

    for (var k in obj) {

        firstKey = k;

        break;

    }

    if (firstKey != null && firstKey[0] == "$") {

        this._validateObject(obj);

    } else {

        this._validateForStorage(obj);

    }

    if (typeof upsert === "object") {

        assert(multi === undefined, "Fourth argument must be empty when specifying upsert and multi with an object.");

        opts = upsert;

        multi = opts.multi;

        upsert = opts.upsert;

    }

    this._db._initExtraInfo();

    this._mongo.update(this._fullName, query, obj, upsert ? true : false, multi ? true : false);

    this._db._getExtraInfo("Updated");

}

参数说明：

        1）query：查询条件，类似于update语句内where后面的内容

        2）obj：update的对象和一些更新的操作符(如$、$inc等)，也可以理解为关系型数据库update语句内set后面的内容

        3）upsert：如果不存在update的纪录，是否插入obj这个新的document。true为插入，默认是false，不插入

        4）multi：默认是false,只更新找到的第一条纪录，如果为true,按条件查出来的多条纪录全部更新。

   update方法至少得接收两个参数:要修改的对象(query)和修改后的对象(obj),而后两个参数它的默认值均为false.下面我再来简单实验下,后两个参数的基本用法.

   首先说说第四个参数multi的作用:默认是false,只更新找到的第一条纪录，如果为true,按条件查出来的多条纪录全部更新.

> db.name.update({fname:"jeff"},{$set:{lname:"li"}},false,false)    #为了让大家看得清楚点,我把后两个值都写了出来,这里可以不用写的,因为默认均为false.这里用到了修改器$set,关于修改器我将在以后介绍

> db.name.find()    #参数multi的值是false,只更新找到的第一条纪录

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "li" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

{ "_id" : ObjectId("50592ead955cfb1fd75066cf"), "fname" : "jeff", "lname" : "chen" }

{ "_id" : ObjectId("50592ecb955cfb1fd75066d0"), "fname" : "jeff", "lname" : "zhao" }

{ "_id" : ObjectId("50592edb955cfb1fd75066d1"), "fname" : "jeff", "lname" : "qian" }

> db.name.update({fname:"jeff"},{$set:{lname:"jiang"}},false,true)

> db.name.find()    #参数multi的值是true,更新找到的所有纪录

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

{ "_id" : ObjectId("50592ead955cfb1fd75066cf"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("50592ecb955cfb1fd75066d0"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("50592edb955cfb1fd75066d1"), "fname" : "jeff", "lname" : "jiang" }

再来看看第三个参数upsert的作用:如果不存在update的纪录，是否插入obj这个新的document。true为插入，默认是false，不插入.

> db.name.update({fname:"jeffery"},{$set:{lname:"jiang"}},false,true)

> db.name.find() #参数upsert的值是false，不插入

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

{ "_id" : ObjectId("50592ead955cfb1fd75066cf"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("50592ecb955cfb1fd75066d0"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("50592edb955cfb1fd75066d1"), "fname" : "jeff", "lname" : "jiang" }

> db.name.update({fname:"jeffery"},{$set:{lname:"jiang"}},true,true)

> db.name.find() #参数upsert的值是true，插入.又学到一种插入数据的方法!

{ "_id" : ObjectId("5059221f955cfb1fd75066cb"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059223a955cfb1fd75066cc"), "fname" : "qiang", "lname" : "he" }

{ "_id" : ObjectId("50592245955cfb1fd75066cd"), "fname" : "deng", "lname" : "pan" }

{ "_id" : ObjectId("50592253955cfb1fd75066ce"), "fname" : "guage", "lname" : "zeng" }

{ "_id" : ObjectId("50592ead955cfb1fd75066cf"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("50592ecb955cfb1fd75066d0"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("50592edb955cfb1fd75066d1"), "fname" : "jeff", "lname" : "jiang" }

{ "_id" : ObjectId("5059357ad3ba22406ad408e6"), "fname" : "jeffery", "lname" : "jiang" }

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