Master MongoDB: Essential CRUD, Queries, Tools, and User Management Guide

MongoDB Introduction

MongoDB supports CRUD operations (Create, Read, Update, Delete) on documents, provides atomic operations on a single document, does not require a predefined schema, and offers its own rich query language. Each document has a unique _id field that MongoDB generates if omitted.

Display Commands

Help                // Show help
db.help()           // Database methods help
show dbs            // List all databases
use <dbName>        // Switch to a database
show collections    // List collections in current DB
show users          // List users
show roles          // List roles
show profile        // Show recent operations >1ms
load('file.js')     // Execute a JavaScript file

CRUD Basics

Insert Documents

# Single insert
use dba
db.test.insert({"name":"zhangya","age":27,"ad":"北京市朝阳区"})
# Multiple insert
db.inventory.insertMany([
  {"item":"journal","qty":25,"size":{"h":14,"w":21,"uom":"cm"},"status":"A"},
  {"item":"notebook","qty":50,"size":{"h":8.5,"w":11,"uom":"in"},"status":"A"},
  {"item":"paper","qty":100,"size":{"h":8.5,"w":11,"uom":"in"},"status":"D"},
  {"item":"planner","qty":75,"size":{"h":22.85,"w":30,"uom":"cm"},"status":"D"},
  {"item":"postcard","qty":45,"size":{"h":10,"w":15.25,"uom":"cm"},"status":"A"}
])

Read Documents

# Find one document
db.inventory.findOne()
# Find all documents
db.inventory.find()
# Query by condition
db.inventory.find({"status":"A"})
# Projection and pretty output
db.inventory.find({"uid":999}).pretty()

Conditional Queries

# Equality
db.inventory.find({"status":"D"})
# Field query
db.inventory.find({"size.uom":"cm"})
# AND condition
db.inventory.find({"size.h":{$gt:10},"status":"D"})
# OR condition
db.inventory.find({$or:[{"qty":{$lt:50}},{"size.uom":"in"}]})
# Regex
db.inventory.find({"status":"A","item":/^p/})

Update Documents

# Update one document
db.inventory.updateOne(
  {"item":"paper"},
  {$set:{"size.uom":"cm","status":"P"},$currentDate:{"lastModified":true}}
)
# Update many documents
db.inventory.updateMany(
  {"qty":{$lt:50}},
  {$set:{"size.uom":"cm","status":"P"},$currentDate:{"lastModified":true}}
)

Delete Documents

# Delete one document
db.inventory.deleteOne({"status":"D"})
# Delete many documents
db.inventory.deleteMany({"status":"P"})

MongoDB Tools

Official documentation: https://docs.mongodb.com/manual/reference/program/

mongod : Main daemon that handles data requests and background management.

mongos : Router for sharded clusters, directs queries to appropriate shards.

mongostat : Provides real‑time statistics of running mongod/mongos instances.

mongotop : Shows time spent reading/writing data per collection.

mongooplog : Polls remote oplog for real‑time migration.

mongoperf : Benchmarks disk I/O performance.

Authentication and Authorization

MongoDB uses role‑based access control. Create the first admin user with db.createUser() and assign roles such as root, readWrite, dbAdmin, etc. Example:

use admin
db.createUser({user:"admin",pwd:"123456",roles:[{role:"root",db:"admin"}]})

Other roles include read, readWriteAnyDatabase, userAdmin, and more. Users are stored in the admin.system.users collection.

Configuration File

# Enable role‑based access control
security:
  authorization: enabled

User Management Examples

Create a database‑specific admin:

use pincheng
db.createUser({user:"pcadmin",pwd:"123",roles:[{role:"dbAdmin",db:"pincheng"}]})

Create a read‑write user for the same database:

use pincheng
db.createUser({user:"user",pwd:"user",roles:[{role:"readWrite",db:"pincheng"}]})

Create a user with different roles on multiple databases:

use test
db.createUser({user:"myTester",pwd:"xyz123",roles:[{role:"readWrite",db:"test"},{role:"read",db:"test2"}]})

View users:

use admin
db.system.users.find().pretty()

Delete users (requires root):

use pincheng
db.dropUser("pcadmin")
use admin
db.dropUser("myTester")

Original source: https://pincheng.xyz/forward/73b3481b.html (Author: BingCheng)