CRUD Operations

CRUD — Create, Read, Update, Delete — forms the backbone of every database interaction. This lesson walks through MongoDB's CRUD methods, from basic single-document operations to advanced bulk writes.

1. Create — Inserting Documents

// Insert a single document
db.students.insertOne({
  name: "Neha Gupta",
  age: 21,
  course: "Computer Science"
})

// Insert multiple documents
db.students.insertMany([
  { name: "Aman Singh", age: 22, course: "Mechanical" },
  { name: "Divya Rao", age: 20, course: "Electronics" }
])

2. Read — Querying Documents

// Find all documents
db.students.find()

// Find with a filter
db.students.find({ course: "Computer Science" })

// Find one document
db.students.findOne({ name: "Neha Gupta" })

// Projection: return only specific fields
db.students.find({ course: "Computer Science" }, { name: 1, age: 1, _id: 0 })

3. Update — Modifying Documents

// Update a single document
db.students.updateOne(
  { name: "Neha Gupta" },
  { $set: { age: 22 } }
)

// Update multiple documents
db.students.updateMany(
  { course: "Mechanical" },
  { $set: { department: "Engineering" } }
)

// Replace an entire document
db.students.replaceOne(
  { name: "Aman Singh" },
  { name: "Aman Singh", age: 23, course: "Mechanical Engineering" }
)

4. Delete — Removing Documents

// Delete a single document
db.students.deleteOne({ name: "Divya Rao" })

// Delete multiple documents
db.students.deleteMany({ course: "Mechanical" })

// Delete all documents (keeps the collection)
db.students.deleteMany({})

5. Advanced: upsert and Bulk Writes

// Upsert: insert if no match is found
db.students.updateOne(
  { name: "Ritika Jain" },
  { $set: { age: 21, course: "Data Science" } },
  { upsert: true }
)

// Bulk write for efficiency
db.students.bulkWrite([
  { insertOne: { document: { name: "Kabir", age: 24 } } },
  { updateOne: { filter: { name: "Kabir" }, update: { $set: { age: 25 } } } },
  { deleteOne: { filter: { name: "Kabir" } } }
])

6. CRUD Checklist

• ✅ Comfortable with insertOne/insertMany
• ✅ Know find(), findOne(), and projections
• ✅ Master $set, $inc, $push, $pull operators
• ✅ Understand upsert behavior
• ✅ Use bulkWrite() for batching operations efficiently