MongoDB Cheat Sheet — CRUD, Queries, Aggregation, and Indexes

db.users.insertOne({ name: "Alice", email: "alice@example.com", age: 30 })

db.users.insertMany([
  { name: "Bob", age: 25 },
  { name: "Charlie", age: 35 }
])

db.users.find()                          // All documents
db.users.find({ age: { $gt: 25 } })     // Where age > 25
db.users.findOne({ email: "alice@example.com" })
db.users.find({}, { name: 1, email: 1 }) // Projection (select fields)
db.users.find().sort({ age: -1 })        // Sort descending
db.users.find().limit(10).skip(20)       // Pagination
db.users.countDocuments({ age: { $gt: 25 } })

db.users.updateOne(
  { email: "alice@example.com" },
  { $set: { age: 31 } }
)

db.users.updateMany(
  { age: { $lt: 18 } },
  { $set: { status: "minor" } }
)

// Other update operators
{ $inc: { age: 1 } }           // Increment
{ $unset: { temp: "" } }       // Remove field
{ $push: { tags: "new" } }     // Add to array
{ $pull: { tags: "old" } }     // Remove from array
{ $addToSet: { tags: "unique" } } // Add if not exists

db.users.deleteOne({ email: "alice@example.com" })
db.users.deleteMany({ status: "inactive" })
db.users.deleteMany({})  // Delete all documents

// Comparison
{ age: { $eq: 30 } }      // Equal
{ age: { $ne: 30 } }      // Not equal
{ age: { $gt: 25 } }      // Greater than
{ age: { $gte: 25 } }     // Greater than or equal
{ age: { $lt: 30 } }      // Less than
{ age: { $in: [25, 30] } } // In array
{ age: { $nin: [25, 30] } } // Not in array

// Logical
{ $and: [{ age: { $gt: 20 } }, { age: { $lt: 30 } }] }
{ $or: [{ status: "active" }, { role: "admin" }] }
{ age: { $not: { $gt: 30 } } }

// Element
{ email: { $exists: true } }
{ age: { $type: "number" } }

// Regex
{ name: { $regex: /^ali/i } }

db.orders.aggregate([
  { $match: { status: "completed" } },
  { $group: {
      _id: "$customerId",
      totalSpent: { $sum: "$amount" },
      orderCount: { $sum: 1 }
  }},
  { $sort: { totalSpent: -1 } },
  { $limit: 10 }
])

// Lookup (join)
db.orders.aggregate([
  { $lookup: {
      from: "users",
      localField: "customerId",
      foreignField: "_id",
      as: "customer"
  }},
  { $unwind: "$customer" }
])

db.users.createIndex({ email: 1 })              // Single field
db.users.createIndex({ email: 1 }, { unique: true }) // Unique
db.users.createIndex({ name: 1, age: -1 })      // Compound
db.users.createIndex({ bio: "text" })            // Text search
db.users.getIndexes()                            // List indexes
db.users.dropIndex("email_1")                    // Drop index