【MongoDB学习笔记8】深入MongoDB的更新（update）操作:修改器$set

MongoDB中文档存入数据库后用update方法更新文档，update方法有两个参数，例如

update（args1,args2）

args1是指查询文档的条件；

args2是指对查询到的文档进行什么样的修改；

一、文档替换

> joe1= db.post.findOne({"age":20}){        "_id" : ObjectId("54a530c3ff0df3732bac1680"),        "id" : 1,        "name" : "joe",        "age" : 20}> joe1.age=2121> db.post.update({"id":1},joe1)WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })>

修改后的结果：

> joe1= db.post.findOne({"age":21}){        "_id" : ObjectId("54a530c3ff0df3732bac1680"),        "id" : 1,        "name" : "joe",        "age" : 21}>

二、使用修改器

1.$set修改器

$set用来指定一个字段的值，如果字段不存在就创建；

> db.post.findOne()   {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65    }

增加comments的键：

> db.post.update({"id":0},    ... {$set:{"comments":"i love you"}})    WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })    > db.post.findOne()    {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65,            "comments" : "i love you"    }    >

修改comments键的值：

> db.post.update({"id":0}, {$set:{"comments":"i don't love you"}})   WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })    > db.post.findOne()    {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65,            "comments" : "i don't love you"    }    >

修改comments的值为数组：

> db.post.update({"id":0}, {$set:{"comments":["i love you","or","i don't love you"]}})   WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })    > db.post.findOne({"id":0})    {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65,            "comments" : [                    "i love you",                    "or",                    "i don't love you"            ]    }    >

删除comments的值：

> db.post.update({"id":0}, {$unset:{"comments":1}})   WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })    > db.post.findOne({"id":0})    {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65    }    >

2.修改内嵌文档

> db.post.findOne({"id":0})    {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65,            "comments" : {                    "1" : 1,                    "2" : 2,                    "3" : 3            }    }    > db.post.update({"id":0}, {$set:{"comments.1":4}})    WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })    > db.post.findOne({"id":0})    {            "_id" : ObjectId("54a530c3ff0df3732bac167f"),            "id" : 0,            "name" : "joe",            "age" : 65,            "comments" : {                    "1" : 4,                    "2" : 2,                    "3" : 3            }    }    >