npodonnell/mongodb_cheatsheet.md

## mongodb_cheatsheet.md

      
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    MongoDB Cheatsheet

N. P. O'Donnell, 2021
Installing Community Edition (Ubuntu)

Check for latest version here
Add MongoDB repository to Apt and install:
MONGO_VERSION=4.4
curl -fsSL https://www.mongodb.org/static/pgp/server-$MONGO_VERSION.asc | sudo apt-key add -
  && echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/$MONGO_VERSION multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-$MONGO_VERSION.list
  && sudo apt update
  && sudo apt install mongodb-org
Enable and start the MongoDB service:
sudo systemctl enable mongod
sudo systemctl start mongod
Check if database is operational:
mongo --eval 'db.runCommand({ connectionStatus: 1 })'
Working in the Shell

Enter the MongoDB shell:
mongo
Security/User Management

First, create a user with a strong password:
> use admin
> db.createUser({user: "user", pwd: passwordPrompt(), roles: []})

Press Ctrl-C to exit the shell.
Edit the mongoDB configuration file (/etc/mongod.conf) and add the following under the security section:
security:
  authorization: enabled

Databases

List databases:
> show databases

Choose a database called foo. If foo doesn't exist MongoDB will create it once the first collection is created:
> use foo

Collections

Create a collection called bar:
> db.createCollection("bar")

Show collections in foo:
> show collections

Drop collection bar:
> db.bar.drop()

Create two more collections called customer and sale:
> db.createCollection("customer")
> db.createCollection("sale")

Insert two records into collection customer:
> db.customer.insert({"name": "alice", "likes": ["makeup", "clothes"]})
> db.customer.insert({"name": "bob", "likes": ["electronics", "sports"]})
> db.customer.insert({"name": "carol", "likes": ["video games"]})

List all the records in collection customer:
> db.customer.find()

List first record in collection customer (alice):
> db.customer.findOne()

List any records in collection customer whose name is bob:
> db.customer.find({name: "bob"})

Print how many records are in the customer collection:
> db.customer.count()

Delete carol from the collection customer:
> db.customer.remove({"name": "carol"})

Delete everything from the collection sale:
> db.sale.remove({})

Delete the customer and sale collections:
db.customer.drop()
db.sale.drop()

Indexes

Get indexes on customer collection:
> db.customer.getIndexes()

Create an ascending index on customer's age attribute:
> db.customer.createIndex({"age": 1})

Create an decending index on customer's age attribute:
> db.customer.createIndex({"age": -1})

Delete all indexes on customer collection:
> db.customer.dropIndexes()

Executing MongoDB Scripts

The mongoDB shell uses Javascript, and .js files may be piped into the shell:
mongo <database name> < <some .js file>
Example:
mongo mydb < generate-report.js
Step-by-Step Replica Set and Authentication


On all nodes, delete all files in /var/lib/mongodb:

rm -fr /var/lib/mongodb/*

Generate key-file on one node:

KEYFILE="/var/lib/mongodb/keyfile"
openssl rand -base64 16 > $KEYFILE
sudo chown root:root $KEYFILE
sudo chmod 400 $KEYFILE


Copy key-file to the other nodes, same location.


Edit /etc/mongod.conf and set the key-file, and authorization to disabled (for now):


security:
  keyFile: /var/lib/mongodb/keyfile
  authorization: disabled
storage:
  dbPath: /var/lib/mongodb
replication:
  replSetName: "rs"

Restart mongod service.