CRUD: insert, find, update, delete

Create

db.users.insertOne({ name: "Ada", age: 36, city: "Pune" })

db.users.insertMany([
  { name: "Alan", age: 41, city: "Delhi" },
  { name: "Grace", age: 29, city: "Pune" }
])

Each insert returns the generated _id. If you do not supply _id, MongoDB creates an ObjectId for you.

Read

db.users.find()                       // all documents
db.users.find({ city: "Pune" })       // filter by equality
db.users.findOne({ name: "Ada" })     // a single document

The first argument to find is the query filter – a document describing what to match. An empty filter matches everything.

Update

Updates need a filter and an update operator. The most common is $set:

db.users.updateOne(
  { name: "Ada" },
  { $set: { city: "Mumbai" }, $inc: { age: 1 } }
)

db.users.updateMany({ city: "Pune" }, { $set: { active: true } })

$set changes fields, $inc increments a number. Use updateMany to change every matching document.

Delete

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

Upsert

Pass { upsert: true } and MongoDB updates the document if it exists or inserts it if it does not – handy for “create or update” logic:

db.users.updateOne(
  { name: "Zoe" },
  { $set: { city: "Chennai" } },
  { upsert: true }
)

Key points

• insertOne/insertMany create documents and return their _id.
• find takes a query filter; an empty filter returns everything.
• Updates combine a filter with operators like $set and $inc.
• upsert: true updates if present, otherwise inserts.