Expression attribute values in DynamoDB

Introduction

Expression attribute values let you safely use values in DynamoDB queries without errors or conflicts.

When you want to insert or update an item with specific values.

When you need to filter items using conditions with values.

When you want to avoid conflicts with reserved words in DynamoDB.

When you want to reuse values in multiple parts of a query safely.

Syntax

DynamoDB

ExpressionAttributeValues = {
  ":key1": value1,
  ":key2": value2
}

Each key starts with a colon (:), like ":val".

Values can be strings, numbers, booleans, or other DynamoDB data types.

Examples

Use this to set the value "Alice" for a name attribute.

DynamoDB

ExpressionAttributeValues = {
  ":name": {"S": "Alice"}
}

Use this to set the value 30 for an age attribute.

DynamoDB

ExpressionAttributeValues = {
  ":age": {"N": "30"}
}

Use this to set a boolean value true for an isActive attribute.

DynamoDB

ExpressionAttributeValues = {
  ":isActive": {"BOOL": true}
}

Sample Program

This command updates the Name attribute of the user with UserId "123" to "Bob" using expression attribute values.

DynamoDB

aws dynamodb update-item \
  --table-name Users \
  --key '{"UserId": {"S": "123"}}' \
  --update-expression "SET #n = :nameVal" \
  --expression-attribute-names '{"#n": "Name"}' \
  --expression-attribute-values '{":nameVal": {"S": "Bob"}}'

Important Notes

Always prefix keys in ExpressionAttributeValues with a colon (:).

Use ExpressionAttributeNames to avoid conflicts with reserved words.

Expression attribute values help prevent injection attacks by separating data from code.

Summary

Expression attribute values store values safely for DynamoDB queries.

They use keys starting with a colon (:), like ":val".

They help avoid errors and reserved word conflicts.