SET expression for adding/changing in DynamoDB

Introduction

The SET expression lets you add new attributes or change existing ones in a DynamoDB item.

You want to update a user's email address in a user profile.

You need to add a new field like 'lastLogin' to an existing record.

You want to increase a numeric counter stored in an item.

You want to change the status of an order from 'pending' to 'shipped'.

Syntax

DynamoDB

UpdateExpression: "SET attributeName = :value, anotherAttribute = :anotherValue"

Use 'SET' to add or change attributes in an item.

Use placeholders like ':value' for the new values to keep the query safe.

Examples

Change the 'age' attribute to a new value.

DynamoDB

UpdateExpression: "SET age = :newAge"

Add or update 'lastLogin' and 'status' attributes at the same time.

DynamoDB

UpdateExpression: "SET lastLogin = :time, status = :newStatus"

Increase the 'score' attribute by a number.

DynamoDB

UpdateExpression: "SET score = score + :increment"

Sample Program

This updates the user's email and increases their login count by 1. If 'loginCount' does not exist, it starts at 0.

DynamoDB

const params = {
  TableName: "Users",
  Key: { userId: "123" },
  UpdateExpression: "SET email = :newEmail, loginCount = if_not_exists(loginCount, :start) + :inc",
  ExpressionAttributeValues: {
    ":newEmail": "[e-mail]",
    ":start": 0,
    ":inc": 1
  },
  ReturnValues: "UPDATED_NEW"
};

// Assume docClient is an instance of AWS.DynamoDB.DocumentClient

const result = await docClient.update(params).promise();
console.log(result.Attributes);

Important Notes

Use if_not_exists to safely add numbers when the attribute might not exist yet.

Always use placeholders (like :newEmail) to avoid injection and errors.

Summary

SET expression updates or adds attributes in DynamoDB items.

Use placeholders for values to keep queries safe and clear.

You can update multiple attributes in one SET expression.