🔄Updating Documents in MongoDB – A Complete Guide

MongoDB, a popular NoSQL database, offers powerful and flexible ways to store, query, and update data. One of the most important operations in a database is updating documents. Whether you're modifying a single field or replacing an entire document, MongoDB provides robust methods to handle updates efficiently.

In this blog, we’ll explore various ways to update documents in MongoDB, covering:

• Types of update operations

• Using the MongoDB shell and drivers

• Update operators and examples

• Best practices

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📌 Understanding MongoDB Update Operations

In MongoDB, the primary methods used for updates are:

1. updateOne() – Updates a single document matching the filter.

2. updateMany() – Updates multiple documents matching the filter.

3. replaceOne() – Replaces the entire document.

4. findOneAndUpdate() – Finds one document and updates it, returning the original or updated document.

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🔧 Syntax Overview

db.collection.updateOne(
   { filter_criteria },
   { update_operator },
   { options }
)

db.collection.updateMany(
   { filter_criteria },
   { update_operator },
   { options }
)

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🛠 Common Update Operators

MongoDB provides various update operators to modify documents:

Operator	Description
$set	Sets the value of a field
$unset	Removes a field
$inc	Increments a field by a value
$push	Adds a value to an array
$pull	Removes a value from an array
$addToSet	Adds a value if it doesn’t already exist in the array

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✅ Examples

1. Update a Single Document (updateOne)

db.students.updateOne(
   { name: "Alice" },
   { $set: { grade: "A" } }
)

➡ Updates the grade field of the student named Alice.

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2. Update Multiple Documents (updateMany)

db.students.updateMany(
   { status: "inactive" },
   { $set: { status: "active" } }
)

➡ Updates all documents where the status is inactive.

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3. Increment a Field ($inc)

db.products.updateOne(
   { name: "Laptop" },
   { $inc: { quantity: -1 } }
)

➡ Decreases the quantity of a laptop by 1.

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4. Push to an Array ($push)

db.users.updateOne(
   { username: "john_doe" },
   { $push: { hobbies: "gardening" } }
)

➡ Adds “gardening” to the user’s list of hobbies.

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5. Replace an Entire Document (replaceOne)

db.orders.replaceOne(
   { order_id: 1001 },
   { order_id: 1001, item: "Tablet", quantity: 3, status: "shipped" }
)

➡ Completely replaces the existing document with a new one.

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⚠️ Important Tips

• Use $set to avoid overwriting entire documents accidentally.

• Always back up critical data before performing bulk updates.

• Use indexes to speed up update queries.

• Use findOneAndUpdate when you need to get a document before or after update.

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📄 Using Options

You can enhance update operations using options like:

• upsert: true – Inserts a document if no match is found.

• returnDocument: "after" – Used with findOneAndUpdate to return the updated document.

Example with upsert:

db.students.updateOne(
   { name: "Bob" },
   { $set: { grade: "B" } },
   { upsert: true }
)

➡ If Bob doesn't exist, a new document is inserted.

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✅ Conclusion

MongoDB's update capabilities are flexible and powerful, suitable for a wide range of use cases — from updating a single field to manipulating arrays and handling missing data. Mastering these operations is crucial for anyone working with MongoDB.

By combining update operators with the right query and options, you can efficiently manage dynamic data in modern applications.

Name: Prachi Deokar

College: Sri Balaji University, Pune

School: School of Computer Studies

Class: TY-BCA(E)