MongoDB--使用修改器修改文档

     可以使用修改器啦修改文档，比如增加、删除文档的键值。使用修改器首先要定位到某个文档， 然后再增加相应的修改选项,需要使用update语句

1.$inc修改器修改文档

> db.users.findOne({'name':'cd'});
{
        "_id" : ObjectId("584eafa97629396db95535da"),
        "name" : "cd",
        "sex" : "M",
        "information" : {
                "age" : 23,
                "address" : "Shanghai"
        }
}
> db.users.update({"name": "cd"},
...    {"$inc":{"qq": 123456789}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.users.findOne({'name':'cd'});
{
        "_id" : ObjectId("584eafa97629396db95535da"),
        "name" : "cd",
        "sex" : "M",
        "information" : {
                "age" : 23,
                "address" : "Shanghai"
        },
        "qq" : 123456789
}
>

  命令解释：

  db.users.findOne() -->查询某个文档，可以添加具体的参数，只返回一个文档，如上例子查询文档键name的值为cd的该文档

  db.users.update() -->更新某个文档，一般带有两个参数，一个参数定位到更新那个文档，另一个参数设置修改内容

 {"$inc":{"key" : "value"}}-->修改键key对应的值，若key不存在，则创建key

 流程：

  1.首先查询name为cd的文档，看文档里面的具体键值

  2.使用修改器$inc和更新语句更新集合中的文档

  3.再次查询name为cd的文档，和步骤1的查询结果对比，看更新文档是否成功

2.$set修改器修改文档

> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549695a14618fbeef3bf0f"),
        "name" : "scd",
        "sex" : "M",
        "address" : "上海"
}
> db.users.update( {"name":"scd"},
...     {"$set":{"lang": ["中文", "english"]}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549695a14618fbeef3bf0f"),
        "name" : "scd",
        "sex" : "M",
        "address" : "上海",
        "lang" : [
                "中文",
                "english"
        ]
}
>

3.$unset修改器，删除文档中的某个键

> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549885a14618fbeef3bf11"),
        "name" : "scd",
        "sex" : "M",
        "address" : "上海",
        "lang" : [
                "中文",
                "english"
        ]
}
> db.users.update({"name":"scd"},
...     {"$unset":{"sex":"M"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549885a14618fbeef3bf11"),
        "name" : "scd",
        "address" : "上海",
        "lang" : [
                "中文",
                "english"
        ]
}
>

操作结果：删除键name值为scd文档的键sex

4.$set和$inc修改器的区别

  $inc只能由于修改整型、长整型或双精度浮点型的值

> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549885a14618fbeef3bf11"),
        "name" : "scd",
        "address" : "上海",
        "lang" : [
                "中文",
                "english"
        ]
}
> db.users.update({"name":"scd"},
...    {"$inc":{"address": "北京"}});
WriteResult({
        "nMatched" : 0,
        "nUpserted" : 0,
        "nModified" : 0,
        "writeError" : {
                "code" : 14,
                "errmsg" : "Cannot increment with non-numeric argument: {address: "鍖椾含"}"
        }
})

使用$inc修改键对应的数值为字符串会报错 "writeError"

而使用$set可以修改键对应的值为字符类型的数值

> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549885a14618fbeef3bf11"),
        "name" : "scd",
        "address" : "上海",
        "lang" : [
                "中文",
                "english"
        ]
}

> db.users.update({"name":"scd"},
...    {"$set":{"address":"北京"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.users.findOne("name":"scd");
2016-12-17T09:55:20.213+0800 E QUERY    [thread1] SyntaxError: missing ) after argument list @(shell):1:23

> db.users.findOne({"name":"scd"});
{
        "_id" : ObjectId("58549885a14618fbeef3bf11"),
        "name" : "scd",
        "address" : "北京",
        "lang" : [
                "中文",
                "english"
        ]
}
>

$set修改器可以修改许多类型的数值，如字符串、数组等等