The very tutorial for starters learning MongoDB

• Author: Sean
• Date created: Feb 14^th, 2023

Contents

• MongoDB installation
• MongoDB and NoSql
• MongoDB services
• Basic MongoDB syntax
  • Access databases' meta data
  • Database level
  • Collection level
• Documents CRUD

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MongoDB Installlation

For various operating systems:

• Ubuntu
• Docker
• MacOS
• Windows

Ubuntu

Official instructions: here

wget -qO - https://www.mongodb.org/static/pgp/server-6.0.asc | sudo apt-key add -

## Here we have to specify Ubuntu version, and we use 16.04 as an example
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/6.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-6.0.list

sudo apt-get update

sudo apt-get install -y mongodb-org

Docker

Official docker image: here

Run docker:

docker run --name some-mongo -d mongo:tag

... where some-mongo is the name you want to assign to your container and tag is the tag specifying the MongoDB version you want. See the list above for relevant tags.

MongoDB service is initialized when the container is running!

Connect to mongoDB via another docker container

docker run -it --network some-network --rm mongo mongosh --host some-mongo test

Access MongoDB shell

docker exec -it some-mongo bash

MacOS

Windows

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MongoDB and NoSql

MongoDB is a source-available cross-platform document-oriented database program. Classified as a NoSQL database program, MongoDB uses JSON-like documents with optional schemas. MongoDB is an NoSql database which is most alike a Sql database.

Sql vs NoSql

Aspects	Sql	NoSql
Data formats	Relational tables with primary keys	Collections and JSON-like documents
Difficulty to scale	Hard to scale	Easy to scale
Scaling pattern	Scale vertically	Scale horizontally
Other characteristics	Data consistensy	Same

MongoDB terminology

Sql	MongoDB
Database	Database
Tables	Collections
Row	Documents
Index	Index
Table joins	\
Primary key	Primary key

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MongoDB services

Start and Stop Mongo service

Start MongoDB service

sudo service mongod start

Stop MongoDB service

sudo service mongod stop

Access MongoDB shell

mongosh

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Basic MongoDB syntax

• Access databases' meta data

These are each database' special collection. To access, we can:

dbname.system.*

Options:

Namespaces	Descriptions
dbname.system.namespaces	List all namespaces
dbname.system.indexes	list all indexes
dbname.system.profile	List database's profile info
dbname.system.users	List all users who can access the database
dbname.local.sources	List slaves' info

• Database level

Show all dbs:

show dbs

Create/Switch to a specific database:

use _DB_NAME_

Notes:

• The defaulf entry db is test.
• MongoDB will automatically create a db if the use-ed one does not exist.

Show current database info

Show current database name:

db

Delete current database

db.dropDatabase()

• Collection level

Create collection

Create a collection:

db.createCollection(name, options)

Options

Or we can directly access a collection without creating it ahead(Assume the we choose the collection name users):

db.users.insertOne({name: "Sean"})

Again, MongoDB will automatically create the collection if it does not exist.

Show collections

show collections
## or: show tables

Delete collections

db.<collection_name>.drop()

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Documents CRUD

• Documents creation

Insert one:

db.collection.insertOne({key: value})

Insert multiple documents:

db.collection.insertMany(
   [ <document 1> , <document 2>, ... ],
   {
      writeConcern: <document>,
      ordered: <boolean>
   }
)

Optional parameters

Notes: In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. If an inserted document omits the _id field, the MongoDB driver automatically generates an ObjectId for the _id field.

• Documents query

Select All Documents in a Collection

db.collection.find({})

Specify Equality Condition

To specify equality conditions, use <field>:<value> expressions:

db.collection.find( { <field1>: <value1>, ... } )

Example:

db.collection.find{ name: "Sean", age: 24 }

To only get part of the fields, we use the second parameter in find() method:

db.collection.find( { <field1>: <value1>, ... }, { <field1>: boolean, <field2>: boolean,... } )

For each field, the boolean indicates if we want this field to be selected.

• If we want this field, we set it to be 1
• If we don't want, we set it to be 0
• If we don't specify, the field is not selected by default
• _id is always selected by default unless we specify it to be 0

Specify Conditions Using Query Operators

Query Operators should be JSON-format:

{ <Query_operator1>: value,  <Query_operator2>: value, ...} 

And we can use Query Operators as values to the keys:

db.collection.find( { age: { $lt: 30} } )

Complete query conditions here

SELECT AND operator

db.collection.find( { key1: value1, key2: value2, ...} )

SELECT OR operator

db.collection.find( { $or: [{key1: value1}, {key2: value2}, ...] )

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Access control and authentication

Create a user

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