MongoDB Cheatsheet

// Show all databases
show dbs

// Create/Switch database
use <database_name>

// Show current database
db

// Drop database
db.dropDatabase()

// Show collections
show collections

// Create collection
db.createCollection("users")

// Drop collection
db.users.drop()

// Insert one document
db.users.insertOne({
  name: "Alex",
  email: "alex@example.com",
  age: 28
})

// Insert multiple documents
db.users.insertMany([
  { name: "Emma", age: 25 },
  { name: "Michael", age: 30 }
])

// Insert with nested documents
db.users.insertOne({
  name: "Sarah",
  contact: {
    email: "sarah@example.com",
    phone: "123-456-7890"
  },
  interests: ["coding", "music"]
})

// Find all documents
db.users.find()

// Find with condition
db.users.find({ age: 25 })

// Find one document
db.users.findOne({ name: "Alex" })

// Pretty print results
db.users.find().pretty()

// Count documents
db.users.countDocuments()

// Distinct values
db.users.distinct("age")

// Query comparison
db.users.find({
  age: { $gt: 25 },    // Greater than
  salary: { $lt: 50000 }, // Less than
  status: { $ne: "inactive" }, // Not equal
  role: { $in: ["admin", "user"] } // In array
})

// Comparison operators
$eq  // Equal
$ne  // Not equal
$gt  // Greater than
$gte // Greater than or equal
$lt  // Less than
$lte // Less than or equal
$in  // In array
$nin // Not in array

// Logical operators
$and: [{ age: { $gt: 25 }}, { status: "active" }]
$or: [{ age: 25 }, { age: 30 }]
$not: { age: 25 }
$nor: [{ age: 25 }, { age: 30 }]

// Element operators
$exists: true  // Field exists
$type: "string" // Field type

// Example queries
db.users.find({
  age: { $gte: 25, $lte: 50 },
  status: { $exists: true },
  "address.city": "New York"
})

// Update one document
db.users.updateOne(
  { name: "Alex" },
  { $set: { age: 29 } }
)

// Update multiple documents
db.users.updateMany(
  { status: "inactive" },
  { $set: { status: "active" } }
)

// Replace document
db.users.replaceOne(
  { name: "Alex" },
  { name: "Alexander", age: 29 }
)

// Update operators
$set     // Set field value
$unset   // Remove field
$inc     // Increment field
$mul     // Multiply field
$rename  // Rename field
$min     // Update if less than
$max     // Update if greater than

// Array updates
$push    // Add to array
$pop     // Remove from array
$pull    // Remove matching elements
$addToSet // Add unique to array

// Push to array
db.users.updateOne(
  { name: "Alex" },
  { $push: { interests: "sports" } }
)

// Push multiple values
db.users.updateOne(
  { name: "Alex" },
  { 
    $push: { 
      interests: { 
        $each: ["reading", "travel"] 
      } 
    } 
  }
)

// Remove from array
db.users.updateOne(
  { name: "Alex" },
  { $pull: { interests: "sports" } }
)

// Add unique values
db.users.updateOne(
  { name: "Alex" },
  { $addToSet: { interests: "coding" } }
)

// Delete one document
db.users.deleteOne({ name: "Alex" })

// Delete multiple documents
db.users.deleteMany({ status: "inactive" })

// Delete all documents
db.users.deleteMany({})

// Delete with complex conditions
db.users.deleteMany({
  $or: [
    { status: "inactive" },
    { lastLogin: { $lt: new Date('2023-01-01') } }
  ]
})

// Basic aggregation
db.users.aggregate([
  { $match: { age: { $gt: 25 } } },
  { $group: { _id: "$status", count: { $sum: 1 } } }
])

// Multiple stages
db.orders.aggregate([
  { $match: { status: "completed" } },
  { $group: {
      _id: "$userId",
      totalSpent: { $sum: "$amount" },
      orderCount: { $sum: 1 }
    }
  },
  { $sort: { totalSpent: -1 } },
  { $limit: 5 }
])

// Common aggregation operators
$match   // Filter documents
$group   // Group documents
$sort    // Sort documents
$limit   // Limit results
$skip    // Skip results
$project // Shape output
$unwind  // Deconstruct array
$lookup  // Join collections

// Group by field
db.sales.aggregate([
  {
    $group: {
      _id: "$category",
      total: { $sum: "$amount" },
      count: { $sum: 1 },
      avg: { $avg: "$amount" },
      max: { $max: "$amount" },
      min: { $min: "$amount" }
    }
  }
])

// Multiple grouping
db.sales.aggregate([
  {
    $group: {
      _id: {
        category: "$category",
        year: { $year: "$date" }
      },
      total: { $sum: "$amount" }
    }
  }
])

// Create index
db.users.createIndex({ email: 1 })

// Create compound index
db.users.createIndex({ 
  email: 1, 
  username: 1 
})

// Create unique index
db.users.createIndex(
  { email: 1 },
  { unique: true }
)

// Text index
db.articles.createIndex(
  { title: "text", content: "text" }
)

// Show indexes
db.users.getIndexes()

// Drop index
db.users.dropIndex("email_1")

// Drop all indexes
db.users.dropIndexes()

// Single field index
db.users.createIndex({ age: 1 })

// Compound index
db.users.createIndex({ age: 1, name: 1 })

// Multikey index (arrays)
db.users.createIndex({ tags: 1 })

// Geospatial index
db.places.createIndex({ location: "2dsphere" })

// Hashed index
db.users.createIndex({ _id: "hashed" })

// Partial index
db.users.createIndex(
  { email: 1 },
  { partialFilterExpression: { age: { $gt: 18 } } }
)