Q3: MongoDB Queries: Design and Develop MongoDB Queries using CRUD operations. (Use CRUD operations, SAVE method, logical operators etc.)

// Create and switch to database
use studentDB;

// Create collection
db.createCollection("students");

// ------------------- CREATE -------------------

// Insert one document
db.students.insertOne({
    name: "Alice",
    age: 21,
    course: "Computer Science"
});

// Insert multiple documents
db.students.insertMany([
    { name: "Bob", age: 22, course: "Mathematics" },
    { name: "Charlie", age: 23, course: "Physics" },
    { name: "David", age: 20, course: "Computer Science" },
    { name: "Eva", age: 22, course: "Mathematics" }
]);

// ------------------- READ -------------------

// Show all student records
db.students.find();

// Find all students aged 22
db.students.find({ age: 22 });

// Find students in Computer Science and age > 20
db.students.find({ course: "Computer Science", age: { $gt: 20 } });

// ------------------- UPDATE -------------------

// Update one student's age
db.students.updateOne(
    { name: "Alice" },
    { $set: { age: 22 } }
);

// Update all Mathematics students to Applied Mathematics
db.students.updateMany(
    { course: "Mathematics" },
    { $set: { course: "Applied Mathematics" } }
);

// ------------------- DELETE -------------------

// Delete one student
db.students.deleteOne({ name: "Bob" });

// Delete all students older than 22
db.students.deleteMany({ age: { $gt: 22 } });

// ------------------- LOGICAL OPERATIONS -------------------

// 1. $and -> Students in Computer Science AND older than 20
db.students.find({
    $and: [
        { course: "Computer Science" },
        { age: { $gt: 20 } }
    ]
});

// 2. $or -> Students aged less than 22 OR studying Physics
db.students.find({
    $or: [
        { age: { $lt: 22 } },
        { course: "Physics" }
    ]
});

// 3. $nor -> Students NOT in Mathematics NOR age = 22
db.students.find({
    $nor: [
        { course: "Mathematics" },
        { age: 22 }
    ]
});