MongoDB

mongosh, queries and updates, indexes, aggregation, mongodump backups and diagnostics.

Connecting

Connect with a connection string

mongosh "mongodb://<user>@<host>:27017/<database>?authSource=admin"

List databases

show dbs

Switch database

use <database>

List collections

show collections

Find documents by a field

db.<collection>.find({ status: "active" }).limit(10)

Find one by _id

db.<collection>.findOne({ _id: ObjectId("<id>") })

Comparison and projection

db.<collection>.find({ age: { $gte: 18 } }, { name: 1, email: 1 })

Sort, skip and limit

db.<collection>.find().sort({ createdAt: -1 }).skip(20).limit(10)

Count documents

db.<collection>.countDocuments({ status: "active" })

Distinct values of a field

db.<collection>.distinct("status")

Insert a document

db.<collection>.insertOne({ name: "Alice", createdAt: new Date() })

Update a field

db.<collection>.updateOne({ _id: ObjectId("<id>") }, { $set: { status: "done" } })

Update many documents

db.<collection>.updateMany({ status: "new" }, { $set: { status: "pending" } })

Delete documents

db.<collection>.deleteMany({ status: "archived" })

Create an index

db.<collection>.createIndex({ email: 1 }, { unique: true })

List indexes

db.<collection>.getIndexes()

Explain a queryadvanced

db.<collection>.find({ email: "a@b.c" }).explain("executionStats")

Group and countadvanced

db.<collection>.aggregate([
  { $match: { status: "active" } },
  { $group: { _id: "$country", count: { $sum: 1 } } },
  { $sort: { count: -1 } }
])

Dump a database

mongodump --uri "mongodb://<user>@<host>:27017/<database>?authSource=admin" --gzip --archive=<database>.gz

Restore a dump

mongorestore --uri "mongodb://<user>@<host>:27017" --gzip --archive=<database>.gz

Collection size and statsadvanced

db.<collection>.stats({ scale: 1024 * 1024 })

Running operations longer than 5 secondsadvanced

db.currentOp({ active: true, secs_running: { $gt: 5 } })

Kill an operationadvanced

db.killOp(<opid>)

Replica set statusadvanced

rs.status()