MongoDB Cheat Sheet

1. MongoDB Basics

• MongoDB is a NoSQL, document-oriented database that stores data in flexible, JSON-like documents.

2. MongoDB Shell Commands

• Start MongoDB shell:

  mongosh

• Show Databases:

  show dbs

• Switch/Create Database:

  use database_name

• Show Collections (tables equivalent):

  show collections

3. Create a Collection

• Create Collection:

  db.createCollection("collection_name")

Collections are created automatically when you insert a document.

4. CRUD Operations

Insert Documents

• Insert One Document:

  db.collection_name.insertOne({key: "value", key2: "value2"})

• Insert Multiple Documents:

  db.collection_name.insertMany([
      {key: "value", key2: "value2"},
      {key: "value3", key2: "value4"}
  ])

Find Documents

• Find All Documents:

  db.collection_name.find()

• Find with Condition:

  db.collection_name.find({key: "value"})

• Pretty Print:

  db.collection_name.find().pretty()

Update Documents

• Update One Document:

  db.collection_name.updateOne({key: "value"}, {$set: {key2: "new_value"}})

• Update Multiple Documents:

  db.collection_name.updateMany({key: "value"}, {$set: {key2: "new_value"}})

Delete Documents

• Delete One Document:

  db.collection_name.deleteOne({key: "value"})

• Delete Multiple Documents:

  db.collection_name.deleteMany({key: "value"})

5. Querying Data

Operators in Queries

• Equality:

  db.collection_name.find({key: "value"})

• Greater Than (GT):

  db.collection_name.find({key: {$gt: value}})

• Less Than (LT):

  db.collection_name.find({key: {$lt: value}})

• In:

  db.collection_name.find({key: {$in: [value1, value2]}})

AND/OR Conditions

• AND Condition (default behavior):

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

• OR Condition:

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

6. Sorting, Limiting, and Pagination

• Sort Results:

  db.collection_name.find().sort({key: 1})   // Ascending
  db.collection_name.find().sort({key: -1})  // Descending

• Limit Results:

  db.collection_name.find().limit(5)

• Skip Results (pagination):

  db.collection_name.find().skip(5).limit(5)

7. Indexes

• Create Index:

  db.collection_name.createIndex({key: 1})

1 for ascending, -1 for descending.

• Show Indexes:

  db.collection_name.getIndexes()

8. Aggregation

• Basic Aggregation:

  db.collection_name.aggregate([
      {$match: {key: "value"}},
      {$group: {_id: "$key2", total: {$sum: "$key3"}}}
  ])

9. Relationships (Embedding vs. Referencing)

• Embedding Documents (Store related data in the same document):

  {
    _id: 1,
    name: "John",
    address: {
      street: "123 St",
      city: "New York"
    }
  }

• Referencing Documents (Store references to related data):

  {
    _id: 1,
    name: "John",
    address_id: ObjectId("507f191e810c19729de860ea")
  }

10. MongoDB Atlas

• MongoDB Atlas is a cloud database service for MongoDB.

Connecting to MongoDB Atlas

• Connection String (from MongoDB Atlas):

  mongodb+srv://<username>:<password>@cluster0.mongodb.net/test

11. Backup and Restore

• Backup Database:

  mongodump --db database_name

• Restore Database:

  mongorestore --db database_name dump/database_name/

12. MongoDB Operators

• $set: Updates the value of a field.
• $inc: Increments the value of a field.
• $push: Appends a value to an array.
• $pull: Removes a value from an array.
• $exists: Checks for the existence of a field.

13. Other Useful Commands

• Count Documents:

  db.collection_name.countDocuments()

• Drop Collection:

  db.collection_name.drop()

• Drop Database:

  db.dropDatabase()

14. Data Types

• Common MongoDB Data Types:
  • String
  • Number (32-bit or 64-bit integer)
  • Boolean
  • Array
  • Object
  • ObjectId
  • ISODate (for date/time)

15. Transactions (MongoDB 4.0+)

• Start Transaction:

  session = db.getMongo().startSession();
  session.startTransaction();

• Commit Transaction:

  session.commitTransaction();

• Abort Transaction:

  session.abortTransaction();