Connecting

Connection String

mongosh "mongodb://localhost:27017"
mongosh "mongodb://user:pass@host:27017/mydb"
mongosh "mongodb+srv://user:pass@cluster.mongodb.net/mydb"

Driver Connection (Node.js)

const { MongoClient } = require('mongodb');
const client = new MongoClient(uri);
await client.connect();
const db = client.db('mydb');

Databases & Collections

Database Operations

show dbs
use mydb
db.dropDatabase()

Collection Operations

db.createCollection("users")
show collections
db.users.drop()

Capped Collection

db.createCollection("logs", {
  capped: true, size: 10485760, max: 5000
})

CRUD Operations

Insert

db.users.insertOne({ name: "Alice", age: 30 })
db.users.insertMany([
  { name: "Bob", age: 25 },
  { name: "Carol", age: 28 }
])

Find

db.users.findOne({ name: "Alice" })
db.users.find({ age: { $gte: 25 } })
db.users.find({}, { name: 1, _id: 0 })
db.users.find().sort({ age: -1 }).limit(10)

Update

db.users.updateOne(
  { name: "Alice" },
  { $set: { age: 31, city: "Boston" } }
)
db.users.updateMany(
  { active: false },
  { $set: { archived: true } }
)

Delete

db.users.deleteOne({ name: "Alice" })
db.users.deleteMany({ active: false })

Replace & Upsert

db.users.replaceOne(
  { name: "Alice" },
  { name: "Alice", age: 32, city: "NYC" }
)
db.users.updateOne(
  { email: "a@ex.com" },
  { $set: { name: "Alice" } },
  { upsert: true }
)

Query Operators

Comparison

$eq / $ne	Equal / not equal
$gt / $gte	Greater than / greater or equal
$lt / $lte	Less than / less or equal
$in / $nin	In array / not in array

Logical

$and	All conditions must match
$or	At least one condition matches
$not	Negates a condition
$exists	Field exists (true/false)
$regex	Regular expression match

Update Operators

$set	Set field value
$unset	Remove field
$inc	Increment numeric value
$push / $pull	Add / remove array element
$addToSet	Add to array if not present
$rename	Rename a field

Aggregation

Pipeline Stages

$match	Filter documents (like WHERE)
$group	Group and aggregate
$project	Reshape documents (like SELECT)
$sort	Sort results
$limit / $skip	Pagination
$lookup	Left outer join with another collection
$unwind	Deconstruct array into documents

Aggregation Example

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

Indexes

Create & Drop

db.users.createIndex({ email: 1 }, { unique: true })
db.users.createIndex({ name: 1, age: -1 })
db.users.createIndex({ location: "2dsphere" })
db.users.dropIndex("email_1")

Index Types

Single field	Index on one field ({ name: 1 })
Compound	Multiple fields ({ a: 1, b: -1 })
Text	Full-text search ({ field: 'text' })
2dsphere	Geospatial queries
TTL	Auto-expire documents after time

Index Info

db.users.getIndexes()
db.users.find({ name: "Alice" }).explain()

Schema Design

Embedding vs Referencing

Embed	1:1 or 1:few, data read together
Reference	1:many, data accessed independently
Embed	Sub-document rarely exceeds 16 MB
Reference	Many-to-many relationships

Schema Validation

db.createCollection("users", {
  validator: { $jsonSchema: {
    bsonType: "object",
    required: ["name", "email"],
    properties: {
      name: { bsonType: "string" },
      email: { bsonType: "string" }
}}}})

Replication

Replica Set Concepts

Primary	Receives all writes
Secondary	Replicates from primary, can serve reads
Arbiter	Votes in elections, holds no data

Replica Set Commands

rs.initiate()
rs.add("mongo2:27017")
rs.addArb("mongo3:27017")
rs.status()
rs.conf()

Common Patterns

Transactions

const session = client.startSession();
session.startTransaction();
await db.collection("accounts").updateOne(
  { _id: 1 }, { $inc: { bal: -100 } }, { session });
await db.collection("accounts").updateOne(
  { _id: 2 }, { $inc: { bal: 100 } }, { session });
await session.commitTransaction();

Bulk Write

db.users.bulkWrite([
  { insertOne: { document: { name: "Dan" } } },
  { updateOne: {
      filter: { name: "Alice" },
      update: { $set: { age: 31 } }
  }},
  { deleteOne: { filter: { name: "old" } } }
])

Change Streams

const stream = db.collection("orders")
  .watch([{ $match: { "fullDocument.status": "new" } }]);
stream.on("change", (change) => {
  console.log(change.fullDocument);
});

mongosh Commands

Shell Helpers

show dbs	List databases
show collections	List collections in current db
db.stats()	Database statistics
db.collection.stats()	Collection statistics
db.collection.countDocuments({})	Count documents
db.collection.distinct('field')	Distinct values for a field

Export & Import

mongoexport --db=mydb --collection=users \
  --out=users.json
mongoimport --db=mydb --collection=users \
  --file=users.json
mongodump --db=mydb --out=/backup/
mongorestore --db=mydb /backup/mydb/

MONGODB QUICK REFERENCE