MongoDB Cheatsheet - MongoDB Command Reference

For backend developers using a document store where reads must stay fast. MongoDB shines at schemaless flexible documents, but that freedom costs you unless you index the fields you filter on. By the end you can design CRUD queries against a collection, read explain("executionStats") to confirm an index is used, build an aggregation pipeline with match/group/sort, and know what a replica set guarantees versus what requires sharding.

Databases·43 commands·Last updated 2026-07-21

Database 6

show dbs

List all databases

use dbname

Switch to a database (created if absent)

db

Show current database

db.stats()

Show current database stats

db.dropDatabase()

Drop current database

show collections

List all collections in current db

Document CRUD 9

db.collection.insertOne({name: "tom"})

Insert one document

db.collection.insertMany([{...}, {...}])

Insert many documents

db.collection.find()

Find all documents

db.collection.find({age: {$gt: 18}})

Conditional query

db.collection.findOne({name: "tom"})

Find one document

db.collection.updateOne({name: "tom"}, {$set: {age: 20}})

Update one document

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

Update many documents

db.collection.deleteOne({name: "tom"})

Delete one document

db.collection.deleteMany({age: {$lt: 18}})

Delete many documents

Query Operators 8

{field: value}

Exact match

{field: {$gt: value}}

Greater than ($gte = gte)

{field: {$lt: value}}

Less than ($lte = lte)

{field: {$ne: value}}

Not equal

{field: {$in: [v1, v2]}}

In list

{$and: [{...}, {...}]}

AND condition

{$or: [{...}, {...}]}

OR condition

{field: /regex/i}

Regex match

Index 6

db.collection.createIndex({field: 1})

Create ascending index (-1 descending)

db.collection.createIndex({f1: 1, f2: 1})

Compound index

db.collection.createIndex({field: 1}, {unique: true})

Unique index

db.collection.createIndex({field: 1}, {expireAfterSeconds: 3600})

TTL index (auto-expire)

db.collection.getIndexes()

List all indexes on a collection

db.collection.dropIndex("index_name")

Drop an index

Aggregation 7

db.collection.aggregate([{$match: {age: {$gt: 18}}}])

Match (filter) stage

{$group: {_id: "$field", count: {$sum: 1}}}

Group & count

{$project: {name: 1, _id: 0}}

Field projection

{$sort: {field: -1}}

Sort

{$limit: 10} / {$skip: 20}

Limit / skip

{$unwind: "$arrayField"}

Unwind array field

{$lookup: {from: "other", localField: "id", foreignField: "_id", as: "joined"}}

Join (like SQL JOIN)

Replication & Sharding 7

rs.status()

Show replica set status

rs.conf()

Show replica set config

rs.initiate()

Initialize replica set

rs.add("host:port")

Add a member

rs.remove("host:port")

Remove a member

sh.status()

Show sharded cluster status

sh.enableSharding("dbname")

Enable sharding for a database

Tips

MongoDB has no fixed schema by default, but use an ORM like Mongoose for validation.
Avoid full collection scans — index large collections and use explain() to inspect the plan.
Use at least 3 replica-set nodes for HA; an odd count avoids split-brain.

Official References

Each command links to its official documentation below, so you can verify the latest usage and read deeper.

Official Docs

Maintained by LaoHand

Publicly updated on Jul 21, 2026, continuously proofread against official docs.

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