One-to-One Relationships

One-to-One Relationships Overview

One-to-One Relationships lets you structure DynamoDB work so it stays readable, testable, and easy to scale. Instead of ad-hoc code, you follow a clear pattern that other developers can recognise immediately.

The key is to keep one-to-one relationships focused and predictable. Start from the minimal example here, then layer in only the complexity your feature actually needs.

// single-table design: many entity types share one table
// USER#42 / PROFILE           -> user profile
// USER#42 / ORDER#2024-001    -> an order for that user
// ORDER#2024-001 / ITEM#1     -> a line item

const key = { pk: 'USER#42', sk: 'ORDER#2024-001' };

Single-table design models relationships through carefully composed partition and sort keys.

One-to-One Relationships 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 One-to-One Relationships example and grow it only as needed.
• Keep configuration explicit so One-to-One Relationships behaves the same in every environment.
• Name things clearly so teammates understand your One-to-One Relationships at a glance.
• Add tests around One-to-One Relationships early to lock in expected behaviour.

Amazon DynamoDB Cheatsheet

Handy DynamoDB (AWS SDK v3) reference related to one-to-one relationships.

How One-to-One Relationships Works in DynamoDB

One-to-One Relationships 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.

Single-table design models relationships through carefully composed partition and sort keys.

• 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 One-to-One Relationships

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

Common Mistakes

• Skipping error handling and edge cases when wiring up one-to-one relationships.
• Leaving one-to-one relationships untested, so regressions slip into production.
• Over-engineering one-to-one relationships before you actually need the extra flexibility.
• Ignoring documentation, which makes one-to-one relationships hard for the next developer to change.

Key Takeaways

• One-to-One Relationships is a core part of working effectively with DynamoDB.
• Start small and keep one-to-one relationships focused on a single responsibility.
• Apply consistent patterns so one-to-one relationships scales across your project.
• Test and document one-to-one relationships to keep it maintainable over time.