MongoDB Basics Cheat Sheet

1. Connecting to MongoDB

Start MongoDB

mongod

---

Connect to MongoDB Shell

mongosh

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Connect to a Specific Database

mongosh <database_name>

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Show Current Database

db

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2. Database Management

List All Databases

show dbs

---

Create or Switch Database

use my_database

---

Delete a Database

db.dropDatabase()

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3. Collection Management

List Collections

show collections

---

Create a Collection

db.createCollection("employees")

---

Delete a Collection

db.employees.drop()

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4. Insert Documents

Insert One Document

db.employees.insertOne({
  name: "Alice",
  position: "Manager",
  salary: 75000
})

---

Insert Multiple Documents

db.employees.insertMany([
  { name: "Bob", position: "Developer", salary: 60000 },
  { name: "Carol", position: "Analyst", salary: 55000 }
])

---

5. Querying Data

Find All Documents

db.employees.find()

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Find with Condition

db.employees.find({ salary: { $gt: 60000 } })

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Find Specific Fields

db.employees.find({}, { name: 1, salary: 1, _id: 0 })

---

Find One Document

db.employees.findOne({ name: "Alice" })

---

Count Documents

db.employees.countDocuments({ position: "Developer" })

---

6. Update Documents

Update One Document

db.employees.updateOne(
  { name: "Alice" },
  { $set: { salary: 80000 } }
)

---

Update Multiple Documents

db.employees.updateMany(
  { position: "Developer" },
  { $set: { position: "Senior Developer" } }
)

---

Replace Document

db.employees.replaceOne(
  { name: "Bob" },
  { name: "Bob", position: "Lead Developer", salary: 70000 }
)

---

7. Delete Documents

Delete One Document

db.employees.deleteOne({ name: "Carol" })

---

Delete Multiple Documents

db.employees.deleteMany({ position: "Analyst" })

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8. Sorting and Limiting

Sort Results

db.employees.find().sort({ salary: -1 })  // -1 for DESC, 1 for ASC

---

Limit Results

db.employees.find().limit(5)

---

Skip Documents

db.employees.find().skip(2)

---

9. Aggregation

Basic Aggregation

db.employees.aggregate([
  { $group: { _id: "$position", avgSalary: { $avg: "$salary" } } }
])

---

Match and Project

db.employees.aggregate([
  { $match: { salary: { $gt: 60000 } } },
  { $project: { name: 1, salary: 1, _id: 0 } }
])

---

10. Indexing

Create an Index

db.employees.createIndex({ name: 1 })

---

List Indexes

db.employees.getIndexes()

---

Drop Index

db.employees.dropIndex("name_1")

---

11. Export and Import Data

Export Data

mongoexport --db=my_database --collection=employees --out=employees.json

---

Import Data

mongoimport --db=my_database --collection=employees --file=employees.json

---

12. Backup and Restore

Backup Database

mongodump --db=my_database --out=/backup/path

---

Restore Database

mongorestore /backup/path

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13. Admin Commands

Show Server Status

db.serverStatus()

---

Show Current Operations

db.currentOp()

---

Kill Operation

db.killOp(<operation_id>)

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Compact Database

db.runCommand({ compact: 'employees' })

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14. User Management

Create Admin User

use admin
db.createUser({
  user: "admin",
  pwd: "password123",
  roles: [{ role: "userAdminAnyDatabase", db: "admin" }]
})

---

Create Database User

db.createUser({
  user: "user1",
  pwd: "pass123",
  roles: [{ role: "readWrite", db: "my_database" }]
})

---

Show Users

show users

---

Delete User

db.dropUser("user1")

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15. Common Query Operators

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Tips for MongoDB

• Backup regularly to avoid data loss.
• Use indexes to improve query performance.
• Prefer embedded documents for better performance.
• Practice aggregation to handle complex queries efficiently.