MongoDB Cheat Sheet

db.users.insertOne({ name: "Alice", age: 30 });
db.users.insertMany([
  { name: "Bob", age: 25 },
  { name: "Carol", age: 35 },
]);

db.users.find({ age: { $gte: 25 } });
db.users.findOne({ email: "alice@example.com" });
db.users.find({ name: /^A/ }, { name: 1, email: 1, _id: 0 });

db.users.updateOne(
  { _id: ObjectId("...") },
  { $set: { name: "Alice Smith" }, $inc: { loginCount: 1 } }
);
db.users.updateMany(
  { active: false },
  { $set: { archived: true } }
);

db.users.deleteOne({ _id: ObjectId("...") });
db.users.deleteMany({ lastLogin: { $lt: ISODate("2025-01-01") } });

{ age: { $gt: 25 } }     // greater than
{ age: { $gte: 25 } }    // greater or equal
{ age: { $lt: 30 } }     // less than
{ status: { $in: ["active", "pending"] } }
{ role: { $nin: ["admin"] } }

{ $and: [{ age: { $gte: 18 } }, { age: { $lte: 65 } }] }
{ $or: [{ status: "active" }, { role: "admin" }] }
{ age: { $not: { $lt: 18 } } }

{ email: { $exists: true } }
{ score: { $type: "number" } }
{ name: { $regex: /^john/i } }
{ tags: { $size: 3 } }

{ tags: "mongodb" }           // contains element
{ tags: { $all: ["db", "nosql"] } }  // contains all
{ "scores.0": { $gt: 90 } }   // first element > 90
{ results: { $elemMatch: { score: { $gte: 90 }, subject: "math" } } }

{ $set: { name: "New Name" } }
{ $unset: { tempField: "" } }
{ $inc: { views: 1 } }
{ $rename: { "oldName": "newName" } }
{ $mul: { price: 1.1 } }  // multiply by 1.1

{ $push: { tags: "new" } }
{ $push: { scores: { $each: [90, 95], $sort: -1, $slice: 5 } } }
{ $pull: { tags: "removed" } }
{ $addToSet: { tags: "unique" } }
{ $pop: { tags: 1 } }  // remove last

db.orders.aggregate([
  { $match: { status: "completed" } },
  { $group: {
    _id: "$customerId",
    total: { $sum: "$amount" },
    count: { $sum: 1 },
    avgAmount: { $avg: "$amount" }
  }},
  { $sort: { total: -1 } }
]);

{
  $lookup: {
    from: "authors",
    localField: "authorId",
    foreignField: "_id",
    as: "author"
  }
},
{ $unwind: "$author" }

{
  $project: {
    fullName: { $concat: ["$first", " ", "$last"] },
    year: { $year: "$createdAt" },
    isActive: { $cond: { if: { $gte: ["$score", 50] }, then: true, else: false } }
  }
}

db.users.createIndex({ email: 1 }, { unique: true });
db.posts.createIndex({ title: "text", body: "text" });
db.orders.createIndex({ userId: 1, createdAt: -1 });

// Auto-delete after 30 days
db.sessions.createIndex({ createdAt: 1 }, { expireAfterSeconds: 2592000 });
// Only index active users
db.users.createIndex({ email: 1 }, { partialFilterExpression: { active: true } });

db.users.find({ email: "a@b.com" }).explain("executionStats");
// Check: executionStats.totalDocsExamined vs nReturned
db.users.getIndexes();

show dbs
use mydb
show collections
db.stats()
db.users.stats()
db.users.countDocuments({ active: true })

mongodump --db=mydb --out=/backup/
mongorestore --db=mydb /backup/mydb/
mongodump --uri="mongodb+srv://..." --gzip --archive=backup.gz