MongoDB Data Update command, operator

One, mongodb Data Update command

MongoDB Update has two commands: Update, save.

1.1update Command

UPDATE command format:

Db.collection.update (Criteria,objnew,upsert,multi)

Parameter description:

Criteria: Query criteria

Objnew:update objects and some update operators

Upsert: If there is no record of update, whether to insert objnew this new document, true to insert, default to False, not to insert.

Multi: The default is false, updating only the first record found. If true, all records that are queried by criteria are updated.

Example: Shell code    > db.classes.insert ({"Name": "C1", "Count": ())    >  Db.classes.insert ({"Name": "C2", "Count": $)    > db.classes.find ()    {  "_id"  : objectid ("5030f3a3721e16c4ab180cd9"),  "name"  :  "C1",  "Count"  : 30  }   {  "_id"  : objectid ("5030F3AB721E16C4AB180CDA"),  "name"  :  "C2" ,  "Count"  : 30 }   >   

Example 1: Modify the class name of count greater than 20 to C3 shell Code > db.classes.update ({"Count": {$gt: 20}},{$set: {"name": "C3"}}) > Db.classes.find () {"_id": ObjectId ("5030F3A3721E16C4AB180CD9"), "name": "C3", "Count": $ {"_id": ObjectId ("50 30F3AB721E16C4AB180CDA ")," name ":" C2 "," Count ": >

Because the values of Upsert and multi are not specified, all defaults to false, as the result shows, only the first record that meets the criteria is modified.

Example 2: Change the class name of count greater than 20 to C4, set Multi to True shell code > db.classes.update ({"Count": {$gt: 20}},{$set: {"name": "C4"}} , false,true) > Db.classes.find () {"_id": ObjectId ("5030F3A3721E16C4AB180CD9"), "name": "C4", "Count": 30} { "_id": ObjectId ("5030F3AB721E16C4AB180CDA"), "name": "C4", "Count": >

Because multi is specified as true, two records that match the criteria are updated.

Example 3: Change the class name of count greater than 50 to C5, set Upsert to True Shell code > db.classes.update ({"Count": {$gt: 50}},{$set: {"name": "C5"}  },true,false) > Db.classes.find () {"_id": ObjectId ("5030F3A3721E16C4AB180CD9"), "name": "C4", "Count": 30} { "_id": ObjectId ("5030F3AB721E16C4AB180CDA"), "name": "C4", "Count": $ {"_id": ObjectId ("5030f589ce8fa8884e6cd44 1 ")," name ":" C5 "} >

There are no records in the collection that count is greater than 50, but because Upsert is specified as true, a new record is inserted if it is not found.

1.2save Command

MongoDB Another update command is save, in the following format:

Db.collection.save (obj)

Obj represents an object that needs to be updated, and MongoDB replaces the Obj object with a record that already exists in the collection if there is already a record of "_id" that is identical to obj, and inserts the Obj object if it does not exist.

This command is relatively simple and the example is omitted.

Second, data update operator

1. $inc

Usage: {$inc: {Field:value}}

Function: Adds value to a field of a number

Example: Add the age of the student named Chenzhou 5 Shell Code > db.students.find () {"_id": ObjectId ("5030f7ac721e16c4ab180cdb"), "name": " Chenzhou "," Age ": #查询结果显示年龄为22 > Db.students.update ({name:" Chenzhou "},{$inc: {age:5}}) #执行修改, increase the age by 5 > Db.students.find () {"_id": ObjectId ("5030f7ac721e16c4ab180cdb"), "name": "Chenzhou", "Age": > #查询结果显示年龄 Is 27, the modification succeeds

2. $set

Usage: {$set: {Field:value}}

Function: Sets the value of a field in a document

Example: Set the age of Chenzhou to 23-year-old shell code > db.students.find () {"_id": ObjectId ("5030f7ac721e16c4ab180cdb"), "name": "Chenzh Ou "," Age ": $ > Db.students.update ({name:" Chenzhou "},{$set: {age:23}}) > Db.students.find () {" _id ": objec TId ("5030f7ac721e16c4ab180cdb"), "name": "Chenzhou", "Age": $ >

As you can see from the results, the age of the update changed from 27 to 23.

3. $unset

Usage: {$unset: {field:1}}

Role: Delete a field

Example: Remove the shell code from the Chenzhou age field