MongoDB database: Pipelines, user management, replica sets, etc.

Aggregation (aggregate): DB. Collection. aggregate ([{pipe: {expression}}])

Db. Collection. Aggregate ([
{Pipe 1:{expression 1}},
{Pipe 2:{expression 2}},
... ...
])

Pipeline 1 results as input to pipeline 2.

$group: grouping {$group: {
_id: ' $gender ',
count:{$sum: 1}
}}

$match: Filter (older than) {$match: {age:{$gt: 19}}}

$project: Projection (same as find second set of parameters, 1 display, 0 not shown) {$project: {_id:0,counter:1}}

$sort: Sort (same as sort, 1 ascending,-1 descending) {$sort: {_id:-1}}

$skip (Skip the number of clauses, same as Skip) {$skip: 2}

$limit (Get how many clauses, same as limit) {$limit: 2}

$unwind (You can split the array into a single document) {$unwind: ' $xxx '}

Index (1: Ascending index, 2: Descending index):d B. Collection. Ensureindex ({Property 1:1, property 2:1})

View the document index DB. Collection. GetIndex ()

Delete Index db. collection. Dropindex (' Index name ')

Role: Root is available only in the Admin database, super account
READ: Allows the user to read the specified database
ReadWrite: Allows the user to read and write to the specified database

To create a super Administrator:
Db.createuser ({User: ' admin ', pwd: ' 123 ', roles:[{role: ' Root ', db: ' Admin '}]})

To enable validation modification/etc/mongodb.conf:

Security
Authorization:enabled

or Auth=true.

To create a normal user with a super Administrator:
Db.createuser ({User: ' User1 ', pwd: ' 123 ', Roles:[{role: ' ReadWrite ', DB: ' Students '}]})

Login: Mongo-u user1-p 123--authenticationdatabase Students

Replica set: Data backup, etc.:
Mongod--bind_ip x.x.x.x--porx 27018--dbpath ~/desktop/t1--replset rs0
Mongod--bind_ip x.x.x.x--porx 27019--dbpath ~/desktop/t2--replset rs0

Connection MONGO--host x.x.x.x--port 27018

Initialize Primary server: >rs.initiate () View status Rs.status ()

Add replica set: Rs.add (' x.x.x.x:27019 ') ')
Delete Replica set: Rs.remove (' x.x.x.x:27019 ') ')

The read operation from the server needs to be set Rs.slaveok ()

Automatic master-Slave switchover: One server shuts down another automatically switches to the primary server.

Database backup: Mongodump-u user1-p 123--authenticationdatabase database name-d backup DATABASE-O storage location

Database recovery: Mongorestore-h server address-D database--dir backup database location to be restored

MongoDB database: Pipelines, user management, replica sets, etc.