MongoDB Update Documents Practice Questions with Solutions

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Introduction

Updating documents is an essential MongoDB skill because real applications constantly need to change existing data. MongoDB provides methods such as updateOne(), updateMany(), and replaceOne() for modifying documents. In this chapter, you will practice updating individual fields, multiple documents, numbers, arrays, nested fields, and complete documents using practical MongoDB queries. MongoDB Update Documents Practice questions with solutions to help you understand the concepts.

Q1. Update one document using updateOne()

Problem Statement

Update Rahul’s course from "Python" to "MongoDB".

MongoDB Command / Query

db.students.updateOne(
    { name: "Rahul" },
    {
        $set: {
            course: "MongoDB"
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

updateOne() updates the first document that matches the filter.

The $set operator changes only the specified field:

$set: {
    course: "MongoDB"
}

Other fields in Rahul’s document remain unchanged.

Q2. Update multiple fields in one document

Problem Statement

Update Rahul’s age to 16 and change his course to "Data Analytics".

MongoDB Command / Query

db.students.updateOne(
    { name: "Rahul" },
    {
        $set: {
            age: 16,
            course: "Data Analytics"
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

You can update multiple fields using a single $set.

Only age and course are changed. Other fields remain intact.

Q3. Increase a numeric field using $inc

Problem Statement

Increase Aman’s age by 1.

MongoDB Command / Query

db.students.updateOne(
    { name: "Aman" },
    {
        $inc: {
            age: 1
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

$inc is used to increase or decrease a numeric value.

For example:

$inc: {
    age: 1
}

increases the age by 1.

To decrease it, you could use:

$inc: {
    age: -1
}

Q4. Update multiple documents using updateMany()

Problem Statement

Change the course of all students currently enrolled in "Python" to "Advanced Python".

MongoDB Command / Query

db.students.updateMany(
    { course: "Python" },
    {
        $set: {
            course: "Advanced Python"
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 3,
  modifiedCount: 3
}

Explanation

updateMany() updates all documents that match the filter.

If three students have course: "Python", all three will be updated.

The actual matchedCount and modifiedCount depend on your collection.

Q5. Add a new field using $set

Problem Statement

Add an active field with the value true to the student named Neha.

MongoDB Command / Query

db.students.updateOne(
    { name: "Neha" },
    {
        $set: {
            active: true
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

$set can update an existing field or create the field if it does not already exist.

The document will now contain:

{
    name: "Neha",
    active: true
}

along with its other existing fields.

Q6. Remove a field using $unset

Problem Statement

Remove the phone field from Rahul’s document.

MongoDB Command / Query

db.students.updateOne(
    { name: "Rahul" },
    {
        $unset: {
            phone: ""
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

$unset removes a field from a document.

The value assigned to the $unset field is not important. An empty string is commonly used:

$unset: {
    phone: ""
}

Q7. Add an item to an array using $push

Problem Statement

Add "React" to Neha’s skills array.

MongoDB Command / Query

db.students.updateOne(
    { name: "Neha" },
    {
        $push: {
            skills: "React"
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

$push adds a new value to an array.

For example, if the original array is:

skills: ["Python", "MongoDB"]

after the update it becomes:

skills: ["Python", "MongoDB", "React"]

Q8. Remove an item from an array using $pull

Problem Statement

Remove "HTML" from Priya’s skills array.

MongoDB Command / Query

db.students.updateOne(
    { name: "Priya" },
    {
        $pull: {
            skills: "HTML"
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

$pull removes array elements that match the specified value.

If the original array is:

skills: ["HTML", "CSS", "JavaScript"]

it becomes:

skills: ["CSS", "JavaScript"]

Q9. Update a nested field

Problem Statement

Change the city inside Rahul’s address document from "Delhi" to "Noida".

MongoDB Command / Query

db.students.updateOne(
    { name: "Rahul" },
    {
        $set: {
            "address.city": "Noida"
        }
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

Dot notation is used to update fields inside nested documents.

"address.city": "Noida"

means:

address
   └── city → Noida

Other fields inside address, such as pincode, are not changed.

Q10. Replace an entire document using replaceOne()

Problem Statement

Replace Aman’s complete student document with a new document containing a name, age, and course.

MongoDB Command / Query

db.students.replaceOne(
    { name: "Aman" },
    {
        name: "Aman",
        age: 18,
        course: "Full Stack Development"
    }
)

Expected Output

{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

Explanation

replaceOne() replaces the entire matching document, except for the _id value, which remains the same when the replacement document does not specify a different _id.

For example, if the old document was:

{
    _id: ObjectId("..."),
    name: "Aman",
    age: 17,
    course: "MongoDB",
    skills: ["Python", "SQL"],
    active: true
}

after replaceOne(), it becomes approximately:

{
    _id: ObjectId("..."),
    name: "Aman",
    age: 18,
    course: "Full Stack Development"
}

Fields such as skills and active are removed because the complete document was replaced.

Key Takeaways

  • updateOne() updates one matching document.
  • updateMany() updates all documents matching a filter.
  • replaceOne() replaces an entire document.
  • $set changes an existing field or creates a new field.
  • $inc increases or decreases numeric values.
  • $unset removes a field.
  • $push adds a value to an array.
  • $pull removes matching values from an array.
  • Dot notation can update fields inside nested documents.
  • matchedCount tells you how many documents matched the filter.
  • modifiedCount tells you how many documents were actually modified.
  • Use replaceOne() carefully because fields not included in the replacement document are removed.

FAQs

1. What is the updateOne() method in MongoDB?

updateOne() updates the first document that matches the specified filter.

db.students.updateOne(
    { name: "Rahul" },
    { $set: { age: 16 } }
)

2. What is the difference between updateOne() and updateMany()?

updateOne() modifies one matching document, while updateMany() modifies all documents that match the filter.

3. What does the $set operator do?

$set changes the value of a field or creates the field if it does not already exist.

{
    $set: {
        course: "MongoDB"
    }
}

4. How can I increase a number in MongoDB?

Use the $inc operator:

{
    $inc: {
        age: 1
    }
}

This increases the value of age by 1.

5. How can I remove a field from a MongoDB document?

Use $unset:

{
    $unset: {
        phone: ""
    }
}

This removes the phone field.

6. How do I add a value to an array in MongoDB?

Use $push:

{
    $push: {
        skills: "React"
    }
}

This adds "React" to the skills array.

7. What is the difference between updateOne() and replaceOne()?

updateOne() changes only the fields specified by update operators such as $set or $inc. replaceOne() replaces the complete matching document with a new document.

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

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