Projection determines which fields are included or excluded in the documents returned by a query.

Example Document

{
    _id: 1,
    name: "Rahul",
    age: 20,
    course: "Java",
    fee: 5000,
    city: "Patna"
}

To display the complete document, use:

db.students.find()

To display only the student's name and course, use projection.

Syntax

db.collection.find(
    { filter },
    { field: 1 }
)

The second argument of find() specifies the projection.

• 1 means include a field.
• 0 means exclude a field.

Example

db.students.find(
    {},
    { name: 1, course: 1 }
)

This returns the name and course fields. The _id field is included by default.

Example result:

{
    _id: 1,
    name: "Rahul",
    course: "Java"
}

Use 1 to include the fields you want to display.

Example 1: Display Name Only

db.students.find(
    {},
    { name: 1 }
)

Example 2: Display Name and Age

db.students.find(
    {},
    { name: 1, age: 1 }
)

Example 3: Display Name, Course, and Fee

db.students.find(
    {},
    {
        name: 1,
        course: 1,
        fee: 1
    }
)

Only the selected fields and the default _id field are returned.

Use 0 to exclude a field from the returned documents.

Example 1: Hide the Age Field

db.students.find(
    {},
    { age: 0 }
)

All fields are returned except age.

Example 2: Hide Mobile Number

db.students.find(
    {},
    { mobile: 0 }
)

Example 3: Hide Address and Fee

db.students.find(
    {},
    {
        address: 0,
        fee: 0
    }
)

This returns the other fields while excluding the specified fields.

MongoDB includes the _id field by default, even when we include other fields. To hide it, explicitly set _id: 0.

Example

db.students.find(
    {},
    {
        _id: 0,
        name: 1,
        course: 1
    }
)

Example result:

{
    name: "Rahul",
    course: "Java"
}

The result contains only the name and course fields.

We can combine a filter with projection. The filter selects matching documents, while projection controls which fields are returned.

Example: Find Java Students

db.students.find(
    { course: "Java" },
    {
        _id: 0,
        name: 1,
        age: 1
    }
)

This selects students enrolled in Java and displays only their names and ages.

Example: Find Students with Fees Above 5000

db.students.find(
    { fee: { $gt: 5000 } },
    {
        _id: 0,
        name: 1,
        fee: 1
    }
)

This returns the name and fee of students whose fees are greater than 5000.

Projection can be combined with sorting and limiting to return a specific number of records with selected fields.

Example: Three Highest-Paid Employees

db.employees.find(
    {},
    {
        _id: 0,
        name: 1,
        salary: 1
    }
)
.sort({ salary: -1 })
.limit(3)

This returns up to three employees with the highest salaries, displaying only their names and salaries.

Example: Five Cheapest Products

db.products.find(
    {},
    {
        _id: 0,
        product_name: 1,
        price: 1
    }
)
.sort({ price: 1 })
.limit(5)

This returns up to five products with the lowest prices and displays only the product name and price.

MongoDB supports embedded documents. We can use dot notation to include a particular nested field.

Example Document

{
    name: "Rahul",
    course: "Java",
    address: {
        city: "Patna",
        state: "Bihar",
        pincode: 800001
    }
}

Display Only the City

db.students.find(
    {},
    {
        _id: 0,
        name: 1,
        "address.city": 1
    }
)

This returns the student's name and the city field from the embedded address document.

• 1 includes a field.
• 0 excludes a field.
• The _id field is included by default.
• You can exclude _id while including other fields.
• In a normal projection, do not mix inclusion and exclusion for ordinary fields.
• The special _id field can be excluded from an inclusion projection.
• Projection changes the returned result, not the stored document.

Create a collection named practice_projection and insert these sample documents:

db.practice_projection.insertMany([
    {
        _id: 1,
        name: "Rahul",
        age: 22,
        course: "Java",
        fee: 5000,
        city: "Patna"
    },
    {
        _id: 2,
        name: "Priya",
        age: 19,
        course: "Python",
        fee: 6000,
        city: "Gaya"
    },
    {
        _id: 3,
        name: "Aman",
        age: 21,
        course: "Java",
        fee: 4500,
        city: "Aurangabad"
    },
    {
        _id: 4,
        name: "Neha",
        age: 20,
        course: "HTML",
        fee: 7000,
        city: "Patna"
    }
])

Complete these tasks:

1. Display only the name field.
2. Display name and age, excluding the _id field.
3. Display all fields except the fee field.
4. Find Java students and display only their names.
5. Display name, course, and fee for every student.
6. Find students whose fee is greater than 5000 and display their names and fees.
7. Display the two highest-paid students with only their names and fees.
8. Explain the difference between including and excluding fields in projection.

Run the insertion command only once, or clear the test collection before inserting the same sample data again.