Top 10 Frequently Used queries in Mongo Database with example

Top 10 Frequently Used queries in Mongo Database with example

This tutorials explains about frequently used queries in MongoDB

How to select database in Mongodb

admin>
admin>use moviesdb;

switched to db moviesdb
moviesdb>

MongoDB List All Collections command

For command line,Below commands list out all collections of a database.

  • show collections
  • show tables
  • db.getCollectionNames()

The above command works in non-scripted and command line works in Mongo Shell Terminal

moviesdb>show collections
comments
movies
sessions
theaters
users

or

moviesdb>show tables
comments
movies
sessions
theaters
users

db.getCollectionNames() returns an array of collection names. It works as command line as well as in code script.

You can use this in Code API from an application

db.getCollectionNames()
[ 'comments', 'users', 'sessions', 'theaters', 'movies' ]

Mongo List all Databases command

show dbs or show database command in shell list out all commands.

show dbs;
admin       40.00 KiB
config     112.00 KiB
ecommerce    8.00 KiB
local       40.00 KiB
moviesdb    28.46 MiB

show users: return an array of users in Mongodb

show users;
["admin"]

show roles: return an array of roles object in Mongodb. Roles object contains role assigned to database and inheritedRoles.

show users;

[
    inheritedRoles: []
  },
  {
    role: 'readWrite',
    db: 'moviesdb',
    isBuiltin: true,
    roles: [],
    inheritedRoles: []
  },
  {
    role: 'userAdmin',
    db: 'moviesdb',
    isBuiltin: true,
    roles: [],
    inheritedRoles: []
  },
  {
    role: 'dbOwner',
    db: 'moviesdb',
    isBuiltin: true,
    roles: [],
    inheritedRoles: []
  },
  {
    role: 'enableSharding',
    db: 'moviesdb',
    isBuiltin: true,
    roles: [],
    inheritedRoles: []
  },
  {
    role: 'dbAdmin',
    db: 'moviesdb',
    isBuiltin: true,
    roles: [],
    inheritedRoles: []
  }
]
moviesdb>

Count of documents in a collection in mongo Shell

countDocuments(): returns number records in a collection

db.users.countDocuments();
185

List of indexes for an collection in Mongodb

db.collection.getIndexes() returns the indexes for a given collection in a Database.

db.user.getIndexes()
[ { v: 2, key: { _id: 1 }, name: '_id_' } ]