How to Use begins_with in DynamoDB Queries and Filters

In DynamoDB, use the begins_with function in a KeyConditionExpression or FilterExpression to find items where an attribute starts with a specific prefix. It works only on string or binary attributes and helps efficiently filter data by matching the beginning of the attribute's value.

Syntax

The begins_with function is used inside expressions like KeyConditionExpression or FilterExpression. It takes two arguments: the attribute name and the prefix string to match.

Example syntax:

begins_with (attribute_name, :prefix)

Here:

• attribute_name is the name of the attribute you want to check.
• :prefix is a placeholder for the prefix value you want to match.

json

KeyConditionExpression: "begins_with(#attr, :prefix)"
ExpressionAttributeNames: {"#attr": "YourAttributeName"}
ExpressionAttributeValues: {":prefix": {"S": "prefixValue"}}

Example

This example shows how to query a DynamoDB table named Products to find items where the ProductID starts with ABC.

python

import boto3

# Create DynamoDB client
client = boto3.client('dynamodb')

response = client.query(
    TableName='Products',
    KeyConditionExpression='begins_with(ProductID, :prefix)',
    ExpressionAttributeValues={
        ':prefix': {'S': 'ABC'}
    }
)

for item in response['Items']:
    print(item)

Output

[{'ProductID': {'S': 'ABC123'}, 'Name': {'S': 'Product One'}}, {'ProductID': {'S': 'ABC456'}, 'Name': {'S': 'Product Two'}}]

Common Pitfalls

• Using begins_with on non-key attributes in KeyConditionExpression: begins_with can only be used on the partition key or sort key in KeyConditionExpression. Trying to use it on other attributes will cause errors.
• Incorrect attribute names: Always use ExpressionAttributeNames if your attribute name is a reserved word or contains special characters.
• Wrong data types: begins_with works only with string or binary types, not numbers.

text

Wrong usage example:
KeyConditionExpression='begins_with(NonKeyAttribute, :prefix)'

Right usage example:
KeyConditionExpression='begins_with(SortKeyAttribute, :prefix)'

Quick Reference

Usage	Description
begins_with(attribute, :prefix)	Checks if attribute starts with prefix
Works in KeyConditionExpression	Filters query by key attribute prefix
Works in FilterExpression	Filters results after query or scan
Only for String or Binary	Cannot use with numbers
Use ExpressionAttributeNames	For reserved or special attribute names

Key Takeaways

Use begins_with to filter items starting with a prefix in queries or scans.

begins_with works only on string or binary attributes, not numbers.

In KeyConditionExpression, use begins_with only on key attributes (partition or sort key).

Use ExpressionAttributeNames to avoid conflicts with reserved words.

begins_with helps efficiently narrow down results by matching attribute prefixes.