MongoDB入门学习(三)：MongoDB的增删查改 - 数据库编程

然后将person的age赋为20，删除country字段，再替换原来查询到的文档，如果一个文档有很多字段，而我们只要修改其中一到两个字段，这种方式就比第一种方式要简单的很多。但是这样就有个问题，如果findOne匹配到第二个mary，更新的时候却更新到了第一个mary，那就会出现"_id"重复的问题。这样就有了修改器的使用，是更新变的更简单高效。

1).$set

$set用来修改指定键的值(也可以是内嵌文档的键)，如果这个键不存在就创建它，如：

> db.people.find()
{ "_id" : ObjectId("53a3b0e633c516902a43a790"), "name" : "mary", "age" : 30, "country" : "US", "school" : { "name" : "BeijingUniversity", "city" : "Beijing" } }
> db.people.update({"name" : "mary"}, {"$set" : {"age" : 20, "school.name" : "QinghuaUniversity"}})
> db.people.find()
{ "_id" : ObjectId("53a3b0e633c516902a43a790"), "name" : "mary", "age" : 20, "country" : "US", "school" : { "name" : "QinghuaUniversity", "city" : "Beijing" } }

2).$unset

$unset用来将键完全删除，如：

> db.people.find()
{ "_id" : ObjectId("53a3a1c1abda49d7dfce102d"), "name" : "mary", "age" : 20, "country" : "US" }
> db.people.update({"name" : "mary"}, {"$unset" : {"country" : 1}})
> db.people.find()
{ "_id" : ObjectId("53a3a1c1abda49d7dfce102d"), "age" : 20, "name" : "mary" }

3).$inc

$inc用来增加已有键的值，当键不存在时创建这个键，再在初始值0的基础上再增加，$inc对应的键必须是数字类型的，如果是别的数据类型就会报错，如：

> db.people.find()
{ "_id" : ObjectId("53a3b0e633c516902a43a790"), "age" : 20, "country" : "US", "name" : "mary" }
> db.people.update({"name" : "mary"}, {"$inc" : {"age" : 1}})
> db.people.find()
{ "_id" : ObjectId("53a3b0e633c516902a43a790"), "age" : 21, "country" : "US", "name" : "mary" }
> db.people.update({"name" : "mary"}, {"$inc" : {"age" : -2}})
> db.people.find()
{ "_id" : ObjectId("53a3b0e633c516902a43a790"), "age" : 19, "country" : "US", "name" : "mary" }
> db.people.update({"name" : "mary"}, {"$inc" : {"country" : 2}})
Cannot apply $inc modifier to non-number

4).$push，$pushAll

$push用来对内置数组的操作，给内置数组添加元素，$push是添加一个元素，$pushAll是添加一个数组，如：

> db.people.find()
{ "_id" : ObjectId("53a3b47733c516902a43a791"), "name" : "mary", "friends" : [  "amy",  "join" ] }
> db.people.update({"name" : "mary"}, {"$push" : {"friends" : "joe"}})
> db.people.find()
{ "_id" : ObjectId("53a3b47733c516902a43a791"), "friends" : [  "amy",  "join",  "joe" ], "name" : "mary" }
> db.people.update({"name" : "mary"}, {"$push" : {"friends" : ["jodan", "mical"]}})
> db.people.find()
{ "_id" : ObjectId("53a3b47733c516902a43a791"), "friends" : [  "amy",  "join",  "joe",  [  "jodan",  "mical" ] ], "name" : "mary" }

5).$addToSet，$each

$addToSet用来给内置数组添加元素，如果数组中已经存在相同值的元素，就不添加，用来避免重复，通常和$each组合使用，$each后面跟一个数组用来添加该数组中的元素如：

> db.people.find()
{ "_id" : ObjectId("53a3c18533c516902a43a794"), "friends" : [  "amy" ], "name" : "mary" }
> db.people.update({"name" : "mary"}, {"$addToSet" : {"friends" : "join"}})
> db.people.find()
{ "_id" : ObjectId("53a3c18533c516902a43a794"), "friends" : [  "amy",  "join" ], "name" : "mary" }
> db.people.update({"name" : "mary"}, {"$addToSet" : {"friends" : {"$each" : ["amy", "join", "jodan"]}}})
> db.people.find()
{ "_id" : ObjectId("53a3c18533c516902a43a794"), "friends" : [  "amy",  "join",  "jodan" ], "name" : "mary" }

6).$pull，$pullAll

$pull用来删除内置数组中的某元素，$pullAll删除某几个元素，如：

 db.people.find()
{ "_id" : ObjectId("53a3c18533c516902a43a794"), "name" : "mary", "friends" : [  "amy",  "join",  "jodan",  "mical" ] }
> db.people.update({"name" : "mary"}, {"$pull" : {"friends" : "amy"}})
> db.people.find()
{ "_id" : ObjectId("53a3c18533c516902a43a794"), "friends" : [  "join",  "jodan",  "mical" ], "nam

MongoDB入门学习(三)：MongoDB的增删查改(二)