mongoDB常用命令

Posted 2020-10-01 smileyes

查询某个字段是否存在

db.student.findOne({name:{$exists:true}})

db.student.findOne({‘department.name‘:{$exists:true}})

db.student.findOne({‘department.name‘:{$exists:false}})

-------------------------------------------------------------------------------

判断map对象是否为空,注意不能通过$gt,$lt来判断size大小，可以利用索引来判断

db.student.find({class: {$not: {$size: 0}}}).limit(2)

db.student..find({‘class.0‘: {$exists: 1}})

----------------------------------------------------------------------------------

判断一个数组的size

db.student..find({‘class‘: {$size: 3}})

db.student.find({ $where: "this.class.length < 3" })

---------------------------------------------------------------------------------

格式化输出

select top 1 *from student;

db.student.findOne()

 

select top 1 *from student where age>15;

db.student.findOne({age:{$gt:15}})

 

select class,department from student where name=‘shell‘ and gender=true;

db.student.findOne({name:shell,gender:true},{class:1,department:1})

---------------------------------------------------------------------------------

游标跳转查询和限定返回的个数

db.department.find().skip(10)

 

select top 10 *from department;

db.department.find().limit(10)

---------------------------------------------------------------------------------

值返回指定字段,第一个map写filter条件，第二个map写返回的字段，默认会返回_id,如果不需要可以设置_id:0

db.student.find({},{name:1,id:1}

db.student.find({},{name:1,id:1,_id:0}

--------------------------------------------------------------------------------------

查询总数

db.student.find().count()

db.student.find({age:{$lt:20}}).count()

-----------------------------------------------------------------------------------

更新和删除某个字段：删除第一个class和修改更新时间为当前时间

db.student.update({id:10005},{$unset:{‘class.0‘:1},$set:{updated:NumberLong(new Date().valueOf()/1000)}})

------------------------------------------------------------------------------------