Expression attribute names in DynamoDB

Introduction

Expression attribute names help you use reserved words or special characters in your DynamoDB queries safely.

When your attribute name is a reserved word in DynamoDB, like 'AND' or 'FOR'.

When your attribute name contains special characters or spaces.

When you want to avoid conflicts with DynamoDB's reserved keywords.

When you want to write cleaner and safer update or filter expressions.

Syntax

DynamoDB

ExpressionAttributeNames = {"#key": "ActualAttributeName"}

Use #key in your expressions instead of ActualAttributeName.

Expression attribute names start with a # symbol and map to the real attribute names.

Use them inside your UpdateExpression, FilterExpression, or ProjectionExpression.

Examples

Use #N to represent the attribute 'AND' which is a reserved word.

DynamoDB

ExpressionAttributeNames = {"#N": "AND"}
UpdateExpression = "SET #N = :val"

Use #A to access an attribute with a space in its name.

DynamoDB

ExpressionAttributeNames = {"#A": "Address City"}
ProjectionExpression = "#A"

Use #D to filter items by the 'FOR' attribute safely.

DynamoDB

ExpressionAttributeNames = {"#D": "FOR"}
FilterExpression = "#D = :dateVal"

Sample Program

This updates the 'AND' attribute of the user with UserId '123' using an expression attribute name #N.

DynamoDB

import boto3

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Users')

response = table.update_item(
    Key={'UserId': '123'},
    UpdateExpression='SET #N = :name',
    ExpressionAttributeNames={'#N': 'AND'},
    ExpressionAttributeValues={':name': 'Alice'}
)

print(response['ResponseMetadata']['HTTPStatusCode'])

Important Notes

Always use expression attribute names when your attribute names are reserved words or contain special characters.

Expression attribute names improve query safety and prevent syntax errors.

You can use multiple expression attribute names in one query by adding more mappings.

Summary

Expression attribute names let you safely use reserved words or special characters in DynamoDB queries.

They start with # and map to real attribute names.

Use them in UpdateExpression, FilterExpression, or ProjectionExpression to avoid errors.