CRUD Operations

After this lesson, you will be able to: Use CRUD operations: insertOne/insertMany, find/findOne, updateOne/updateMany, deleteOne/deleteMany.

Mongo's CRUD API is verbose compared to SQL but explicit. Once memorized, it's predictable.

Prerequisites:MongoDB Fundamentals

INSERT operations

Single + bulk inserts.

css

// Single doc
db.users.insertOne({ name: "Alex", email: "[email protected]" });
// → returns { acknowledged: true, insertedId: ObjectId("...") }

// Many docs (atomic per-doc; partial inserts possible if errors)
db.users.insertMany([
  { name: "Sam", email: "[email protected]" },
  { name: "Jordan", email: "[email protected]" }
], { ordered: false });   // ordered:false continues after errors

FIND — read documents

Query filter syntax.

tsx

// All
db.users.find();

// Filter
db.users.find({ age: 30 });
db.users.find({ "address.city": "NYC" });   // nested field

// Projection, only return specific fields (1 = include, 0 = exclude)
db.users.find({ age: 30 }, { name: 1, email: 1, _id: 0 });

// Sort + limit + skip (pagination)
db.users.find().sort({ createdAt: -1 }).limit(10).skip(20);

// findOne, single doc or null
const alex = db.users.findOne({ email: "[email protected]" });

// Count
db.users.countDocuments({ age: { $gte: 18 } });

UPDATE operations

Atomic update operators.

css

// Update one (first match)
db.users.updateOne(
  { email: "[email protected]" },
  { $set: { name: "Alex Chen", updatedAt: new Date() } }
);

// Update many
db.users.updateMany(
  { active: false },
  { $set: { archivedAt: new Date() } }
);

// Common operators
// $set, set field
// $unset, remove field
// $inc, increment a numeric field
// $push, append to array
// $addToSet, append if not already present
// $pull, remove matching elements from array
// $currentDate, set to current date

// Example: increment a counter + push to array atomically
db.posts.updateOne(
  { _id: postId },
  {
    $inc: { viewCount: 1 },
    $push: { recentViewers: { userId, at: new Date() } }
  }
);

// Upsert (insert if not found)
db.users.updateOne(
  { email: "[email protected]" },
  { $set: { name: "New", createdAt: new Date() } },
  { upsert: true }
);

DELETE operations

Same pattern as update.

css

// Delete one
db.users.deleteOne({ email: "[email protected]" });

// Delete many
db.users.deleteMany({ archivedAt: { $exists: true } });

// Soft delete pattern (mark instead of remove)
db.users.updateOne(
  { _id: userId },
  { $set: { deletedAt: new Date() } }
);
// Then your app filters out { deletedAt: null }

Common mistakes

Forgetting $set: `updateOne({_id}, { name: 'X' })` REPLACES the entire doc. Read-modify-write instead of atomic operators (lost-update bug). deleteMany({}), empties the collection (forgot the filter? Disaster). Not handling 'not found' on updateOne (matchedCount = 0 silently).

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