【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=21
21
>
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
}
}
>