The show dbs command displays the databases that contain stored data.

show dbs

Example output:

admin       40.00 KiB
config      72.00 KiB
local       80.00 KiB
school      40.00 KiB

Note: A database may not appear in show dbs until data has been stored in it.

Use the use command to switch to a database. If the database does not exist, MongoDB selects it and creates it when data is first stored.

use school

Output:

switched to db school

Check the current database:

db

A collection stores documents. Use createCollection() to create one explicitly.

db.createCollection("students")

List the collections in the current database:

show collections

The insertOne() method inserts one document into a collection.

db.students.insertOne({
    name: "Rahul",
    age: 20,
    course: "ADCA"
})

To insert multiple documents, use insertMany().

db.students.insertMany([
    {
        name: "Amit",
        age: 21,
        course: "Tally Prime"
    },
    {
        name: "Priya",
        age: 19,
        course: "Web Development"
    },
    {
        name: "Neha",
        age: 22,
        course: "Python"
    }
])

The find() method retrieves documents from a collection.

Display all students:

db.students.find()

Display students in a readable format:

db.students.find().pretty()

Find students whose course is ADCA:

db.students.find({
    course: "ADCA"
})

Find one matching document:

db.students.findOne({
    name: "Rahul"
})

Use updateOne() to update the first document matching a condition.

db.students.updateOne(
    { name: "Rahul" },
    { $set: { age: 21 } }
)

The $set operator changes the specified field without replacing the entire document.

Use updateMany() to update every matching document.

db.students.updateMany(
    { course: "ADCA" },
    { $set: { status: "Active" } }
)

The deleteOne() method deletes the first matching document.

db.students.deleteOne({
    name: "Rahul"
})

The deleteMany() method deletes all documents matching the given condition.

db.students.deleteMany({
    status: "Inactive"
})

Warning: Always check your filter before running a delete command. An incorrect filter can remove more documents than intended.

Use countDocuments() to count documents matching a condition.

Count all student documents:

db.students.countDocuments({})

Count students enrolled in ADCA:

db.students.countDocuments({
    course: "ADCA"
})

Use sort() to arrange documents and limit() to restrict the number of results.

Sort students by age in ascending order:

db.students.find().sort({
    age: 1
})

Sort students by age in descending order:

db.students.find().sort({
    age: -1
})

Display only the first two documents:

db.students.find().limit(2)

The drop() method removes a collection.

db.students.drop()

To remove the current database, use:

db.dropDatabase()

Important: These commands permanently remove database objects or data. Use them only in a practice database when you are learning.

Complete these tasks in MongoDB Shell (mongosh):

1. Create or select a database named school.
2. Create a collection named students.
3. Insert five student documents with name, age, and course.
4. Display all student documents.
5. Find students who are enrolled in Python.
6. Update one student's age.
7. Count all student documents.
8. Display students in descending order of age.