CRUD operations in MongoDB

Query Operators in MongoDB Query operators are used to filter data . Comparison Operators $gt → greater than $lt → less than $gte → greater than or equal $lte → less than or equal $ne → not equal Example: db.users.find({ age: { $gt: 25 } }) Logical Operators $and → all conditions must match $or → any condition matches $not → reverse condition Example: db.users.find({ $or: [ { age: 25 }, { age: 30 } ] }) Element Operators $exists → checks if field exists $type → checks data type 🔹 Sort, Limit, Skip Sort Used to order results db.users.find().sort({ age: 1 }) 1 → ascending -1 → descending Limit Restrict number of results db.users.find().limit(5) Skip Skip some documents db.users.find().skip(5) Used for pagination (like page 2, page 3) Dot Notation Used to access nested fields (data inside objects) . Example document: name: "Rahul" address: { city: "Hyderabad", pincode: 500001 } Query: db.users.find({ "address.city": "Hyderabad" }) “address.city” is dot notation BSON Data Types MongoDB stores data in BSON (Binary JSON) . Common types: String → "Rahul" Number → 25 Boolean → true/false Array → [1, 2, 3] Object → { city: "Hyd" } Date → ISODate Null BSON supports more types than JSON ObjectId is a special BSON type used for _id . Automatically created for each document Example: _id: ObjectId("661f8c9a2f1b2c3d4e5f6789") What ObjectId contains Timestamp (when created) Machine ID Process ID Counter That’s why it is unique Simple Understanding Query operators → filter data Sort → order data Limit → restrict results Skip → pagination Dot notation → access nested fields BSON → data format ObjectId → unique identifier  1. Insert Multiple Documents db.users.insertMany([ { name: "Rahul", age: 25 }, { name: "Anu", age: 22 } ])  Used when you want to add many records at once 2. Find with Conditions db.users.find({ age: { $gt: 23 } }) $gt means “greater than”  Returns users whose age is more than 23 Other operators: $lt → less than $gte → greater than or equal $lte → less than or equal 3. Find Specific Fields db.users.find({}, { name: 1, age: 1 })  Shows only name and age 1 means show field, 0 means hide 4. Update Multiple Documents db.users.updateMany( { age: { $lt: 25 } }, { $set: { status: "young" } } ) Adds/updates field status for many users 🔹 5. Remove a Field db.users.updateOne( { name: "Rahul" }, { $unset: { age: "" } } ) Deletes the age field from document 6. Count Documents db.users.countDocuments() Returns total number of documents With condition: db.users.countDocuments({ age: 25 }) 🔹 7. Sort Data db.users.find().sort({ age: 1 }) 1 → ascending -1 → descending 🔹 8. Limit Results db.users.find().limit(2) Returns only first 2 documents 🔹 9. Skip Documents db.users.find().skip(2) Skips first 2 documents Used in pagination (like page 2, page 3) 🔹 10. Drop Database db.dropDatabase() Deletes entire database ⚠️ (use carefully)