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MongoDB Basics

MongoDB Basics#

What is it?#

  • Mongodb is a general-purpose document database.
  • Scale-out and sharding is a first class citizen
  • Build for ease of development and scaling

Key Aspects#

  • Data is stored as JSON Documents
  • The fields in a JSON document can vary from document to document - unlike Relation Databases.
  • Allows to work with complex, fast-changing and messy data.
  • It enables developers to quickly deliver new application functionality

Advantages of documents:

  • Documents correspond to native data types in many programming languages.
  • Embedded documents and arrays reduce need for expensive joins.
  • Dynamic schema supports fluent polymorphism.
  • Group of documents
  • Like a SQL table with no Schema
  • Each collection is associated with one MongoDB database.
Replica Sets#
  • When you create a database in MongoDB, the system automatically creates at least two more copies of the data, referred to as a replica set.
  • Continuously replicate data between them, offering redundancy and protection against downtime in the face of a system failure or planned maintenance
  • Modern systems: Big clusters of small machines
  • MongoDB shards data at the collection level, distributing documents in a collection across the shards in a cluster.
  • Improve query speed
  • Important to know what can speed up and what index to use
Aggregation Pipelines#
  • Data processing pipelines
Supported Languages#


There is a push to make you use the cloud versions to get started but it is a bit lower down in the docs how to run community edition on mac, linux or windows

MongoDB 5.0 Community Edition supports macOS 10.14 or later.

Damn, perhaps I can use a container for it.

Run a Mongo Container with Docker#
mkdir local_mongo_data
docker run --name mongodb -d -p 27017:27017 -v /my-abs-path/local_mongo_data:/data/db mongo
  • -p 27017:27017: This exposes the port 27017 locally to the containers 27017 port
  • -v ./local_mongo_data:/data/db: Persists data locally from the container

Enter the bash shell:

docker exec -it mongodb bash

There are 2 mongo shells: mongo and mongosh



There are 3 versions of mongo:

  • MongoDB Community: Open-source, community version
  • MongoDB Enterprise
  • Mongo DB Atlas: Managed Service

Query API#


  • Create
  • Read
  • Update
  • Delete
  • Data Aggregation
  • Text-search and geospatial queries

There is a mapping from SQL to mongo queries reference

High Performance#

  • Support for embedded data models reduces I/O activity on database system.
  • Indexes support faster queries and can include keys from embedded documents and arrays.

High Availability#

Replica sets provide:

  • automatic failover
  • data redundancy

Horizontal Scalability#

  • Sharding across clusters
  • Zones

Support for Multiple Storage Engines#

  • Wired tiger - encrypted at rest
  • In-memory

Getting Started#

Mongo DB Shell#

  • db - refers to current db
  • show dbs - list dbs available
  • use db - switch to another db (automatically created when you add data)

Databases and Collections#

MongoDB stores data records as documents - BSON documents - a binary representation of json.

Create a database:

db.myNewCollection1.insertOne({ x: 1 })

This creates the database, collection and document - if they don’t already exist

You can explictly create a collection:


In Mongo 3.2 and onwards you can enforce a schema / validation with Document Validation - ensuring al the documents have the same fields.

Unique Identifiers#

Collections are assigned an immutable UUID.

Retrieve UUIDs for collections: