MongoDB Cheat Sheet

MongoDB user?

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It's a cheat sheet of all the basics of MongoDB:

Key Concepts

What is MongoDB?

MongoDB is a document-based database for flexibility, scalability, and rich querying. It stores data in BSON format, a binary representation of JSON documents, providing additional data types over JSON.

Database Structure

  • Database: A database is a logical grouping of collections. Each database has its own set of files on the file system, usually associated with a single application.
  • Collection: A collection is a group of MongoDB documents analogous to a table in relational databases but without a predefined schema.
  • Document: A BSON document representing a data record. Each document has a dynamic schema of field and value pairs. Documents can contain nested documents, arrays, and arrays of documents.
  • Field: A key-value pair in a document. Fields in documents in the same collection can vary, and the data type of a field's value can be any BSON data type, including another document, an array, or an array of documents.
  • Primary Key: The unique _id field in each document. If not specified, MongoDB generates an ObjectId for it automatically.

Advantages of MongoDB

  • Flexibility: Dynamic schemas allow for documents in the same collection to have different fields.
  • Scalability: Easily scales horizontally with sharding.
  • Performance: Offers high performance for read and write operations and supports indexes for efficient queries.
  • Rich Query Language: Supports a powerful query language to filter and manipulate data.

MongoDB Shell Commands 🍃🌲

Basic Operations

  • Show Databases: show dbs
  • Use Database: use <database_name>
  • Show Collections: show collections
  • Create Collection: db.createCollection("<collection_name>")
  • Drop Database: db.dropDatabase()
  • Drop Collection: db.<collection_name>.drop()

Document Operations

  • Insert a Document: db.<collection_name>.insertOne({<key>: <value>})
  • Insert Multiple Documents: db.<collection_name>.insertMany([{<key>: <value>}, {...}])
  • Find Documents: db.<collection_name>.find()
  • Find Documents with Query: db.<collection_name>.find({<key>: <value>})
  • Find One Document: db.<collection_name>.findOne({<key>: <value>})
  • Update a Document: db.<collection_name>.updateOne({<filter>}, {$set: {<key>: <value>}})
  • Delete a Document: db.<collection_name>.deleteOne({<key>: <value>})

Advanced Queries and Operations

  • Count Documents: db.<collection_name>.countDocuments({<query>})
  • Limit Documents: db.<collection_name>.find().limit(<number>)
  • Sort Documents: db.<collection_name>.find().sort({<key>: 1}) // 1 for ascending, -1 for descending
  • Aggregation Framework: db.<collection_name>.aggregate([{$group: {_id: "$<field>", total: {$sum: 1}}}])

Query Modifiers

  • Comparison Operators: $gt, $gte, $lt, $lte, $ne for greater than, greater than or equal, less than, less than or equal, and not equal conditions.
  • Logical Operators: $and, $or to combine multiple query conditions.
  • Element Operators: $exists, $type to query documents based on the presence of a field or the type of its value.


  • Create Index: db.<collection_name>.createIndex({<key>: 1}) // 1 for ascending, -1 for descending

Additional Tips

  • MongoDB supports ACID transactions for multi-document operations, enhancing application consistency.
  • Use MongoDB Atlas for a managed database service with built-in best practices for security, backup, and monitoring.
Avatar for Niall Maher

Written by Niall Maher

Founder of Codú - The web developer community! I've worked in nearly every corner of technology businesses; Lead Developer, Software Architect, Product Manager, CTO and now happily a Founder.


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