为什么要使用修改器？
通常我们只会修改文档的一部分，这时候更新整个文档就显得很麻烦，通常是通过原子性的更新修改器来完成。
1."$set"修改器
"$set"用来指定某个字段，如果不存在，则创建。这对部分更新或者添加来说就非常方便了。
如:
step1:往users数据库长如一条数据，通过JavaScript来完成：
var logs={name:"joe",age:30,sex:"female",location:"Wisconsin"}
logs
运行：
1 /* 1 */
2 {
3 "name" : "joe",
4 "age" : 30.0,
5 "sex" : "female",
6 "location" : "Wisconsin"
7 }
step2:放入users数据库
db.users.insert(logs)
查询结果:
db.users.find()
/* 1 */
{
"_id" : ObjectId("575a2acfbc9fb3f12145a004"),
"name" : "joe",
"age" : 30.0,
"sex" : "female",
"location" : "Wisconsin"
}
step3:加入要插入一条喜欢的书籍:
db.users.update({name:"joe"},{"$set":{"favorite book":"War and Peace"}})
然后查询db.users.find()
/* 1 */
{
"_id" : ObjectId("575a2acfbc9fb3f12145a004"),
"name" : "joe",
"age" : 30.0,
"sex" : "female",
"location" : "Wisconsin",
"favorite book" : "War and Peace"
}
从结果总可以看出，数据中添加了一条favorite book字段,达到了我们想要的结果^_^;
step4:如果joe喜欢另一本书，继续来看"$set"如何大发神威；
/* 1 */
{
"_id" : ObjectId("575a2acfbc9fb3f12145a004"),
"name" : "joe",
"age" : 30.0,
"sex" : "female",
"location" : "Wisconsin",
"favorite book" : "forrest gump"
}
"$Set"还可以修改键的类型，比如喜欢的是好多书，就可以放在数组中。
如下:
db.users.update({name:"joe"},{"$set":{"favorite book":["cat's Cradle","Foundation Trilogy","Ender's Game"]}})
/* 1 */
{
"_id" : ObjectId("575a2acfbc9fb3f12145a004"),
"name" : "joe",
"age" : 30.0,
"sex" : "female",
"location" : "Wisconsin",
"favorite book" : [
"cat's Cradle",
"Foundation Trilogy",
"Ender's Game"
]
}
还可以通过"$unset"来操作删除某个字段
db.users.update({name:"joe"},{"$unset":{"favorite book":1}})
/* 1 */
{
"_id" : ObjectId("575a2acfbc9fb3f12145a004"),
"name" : "joe",
"age" : 30.0,
"sex" : "female",
"location" : "Wisconsin"
}
这样就和最开始一样了。
"$set"还可以修改内嵌的文档
如:
var log={title:"A Blog Post",content:"...",author:{name:"joe",email:"joe@qq.com"}}
log
db.blog.posts.insert(log)
db.blog.posts.findOne()
/* 1 */
{
"_id" : ObjectId("575a313fbc9fb3f12145a008"),
"title" : "A Blog Post",
"content" : "...",
"author" : {
"name" : "joe",
"email" : "joe@qq.com"
}
}
db.blog.posts.update({"author.name":"joe"},{"$set":{"author.name":"joe Mather"}})
/* 1 */
{
"_id" : ObjectId("575a313fbc9fb3f12145a008"),
"title" : "A Blog Post",
"content" : "...",
"author" : {
"name" : "joe Mather",
"email" : "joe@qq.com"
}
}
总结:$开头的修改器都是通过主键key来修改对应的内容。