Coding⏱️ 2 min read📅 2026-06-03

How to Fix: Update MongoDB field using value of another field

Update MongoDB field using value of another field in a single update operation.

Quick Answer: $set operator is used to update fields with values from other fields.

📋 Table of Contents

  1. 💡 Why You Are Getting This Error
  2. 🚀 How to Resolve This Issue
  3. 🎯 Final Words

In MongoDB, it is indeed possible to update the value of a field using the value from another field. The issue you're encountering arises because MongoDB does not directly support string concatenation like SQL does. Instead, you can use the `$concat` operator in MongoDB.

💡 Why You Are Getting This Error

  • The problem lies in the fact that MongoDB does not support string concatenation like SQL. To fix this, you need to use the `$concat` operator.

🚀 How to Resolve This Issue

Method 1: Using the $concat Operator

  1. Step 1: In your MongoDB update query, use the `$concat` operator to concatenate the values of `firstName` and `lastName.

Method 2: Using Aggregation Pipelines

  1. Step 1: Create an aggregation pipeline that updates the `name` field using the `$concat` operator.

🎯 Final Words

By following these methods, you can update the value of a field in MongoDB using the value from another field.

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