GSI Projections

GSI Projections is an important part of building production-ready DynamoDB systems. This lesson explains what gsi projections means, how it works, and how to apply it with practical examples you can reuse.

GSI Projections Overview

GSI Projections is a building block you will reach for often in DynamoDB. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn gsi projections properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real DynamoDB projects.

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient, QueryCommand } from '@aws-sdk/lib-dynamodb';

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

const { Items } = await docClient.send(new QueryCommand({
  TableName: 'Orders',
  KeyConditionExpression: 'pk = :pk AND begins_with(sk, :prefix)',
  ExpressionAttributeValues: { ':pk': 'USER#42', ':prefix': 'ORDER#' },
  Limit: 25,
}));

QueryCommand reads a partition efficiently using key conditions; add IndexName for a GSI.

GSI Projections Example

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient } from '@aws-sdk/lib-dynamodb';

const docClient = DynamoDBDocumentClient.from(new DynamoDBClient({}));
// docClient.send(new PutCommand(...)) etc.

Start from a minimal GSI Projections example and grow it only as needed.
Keep configuration explicit so GSI Projections behaves the same in every environment.
Name things clearly so teammates understand your GSI Projections at a glance.
Add tests around GSI Projections early to lock in expected behaviour.

Amazon DynamoDB Cheatsheet

Handy DynamoDB (AWS SDK v3) reference related to gsi projections.

Operation	Command	Purpose
Create/replace	`PutCommand`	Write an item
Read one	`GetCommand`	Fetch by primary key
Update	`UpdateCommand`	Modify attributes
Delete	`DeleteCommand`	Remove an item
Query	`QueryCommand`	Efficient key-based read
Scan	`ScanCommand`	Full-table read (avoid)
Transaction	`TransactWriteCommand`	Atomic multi-item writes

How GSI Projections Works in DynamoDB

GSI Projections builds on DynamoDB's key-value and document model, where every item lives in a partition chosen by its partition key and is optionally ordered by a sort key.

QueryCommand reads a partition efficiently using key conditions; add IndexName for a GSI.

Design access patterns first, then model keys around them.
Prefer Query over Scan for predictable performance.
Use expressions to read and write only what you need.
Keep items small and avoid hot partitions.

Practical Guidance for GSI Projections

In production, gsi projections should be cost-aware and resilient. Right-size capacity, handle throttling with retries, and lean on indexes to support your query patterns.

Concern	Recommendation
Performance	Query by key; avoid table scans
Cost	Use on-demand or right-sized provisioned capacity
Modeling	Design for known access patterns
Reliability	Retry throttled requests with backoff

Common Mistakes

Copying gsi projections snippets without understanding what each line does.
Skipping error handling and edge cases when wiring up gsi projections.
Leaving gsi projections untested, so regressions slip into production.
Over-engineering gsi projections before you actually need the extra flexibility.

Key Takeaways

GSI Projections is a core part of working effectively with DynamoDB.
Start small and keep gsi projections focused on a single responsibility.
Apply consistent patterns so gsi projections scales across your project.
Test and document gsi projections to keep it maintainable over time.

Pro Tip

Pair gsi projections with automated tests from day one. It is far cheaper to catch DynamoDB regressions in CI than in production.