DynamoDB

Learning objectives#

• Design a table with partition and sort keys
• Write and read items
• Query by key
• Choose on-demand or provisioned capacity

Explanation#

Items are identified by a primary key: a partition key alone, or a partition key + sort key. The partition key spreads data across storage partitions.

Design tables around access patterns. Query reads items with the same partition key (optionally filtered by sort key); Scan reads the whole table and should be avoided.

Global secondary indexes (GSIs) support extra access patterns.

On-demand capacity bills per request and scales automatically; provisioned capacity is cheaper for steady traffic.

Code example: Orders by customer#

1import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
2import { DynamoDBDocumentClient, PutCommand, QueryCommand } from '@aws-sdk/lib-dynamodb';
3

4const db = DynamoDBDocumentClient.from(new DynamoDBClient({ region: 'ap-south-1' }));
5// Table "Orders": partition key customerId (S), sort key orderDate (S)
6

7await db.send(new PutCommand({
8  TableName: 'Orders',
9  Item: { customerId: 'c-1', orderDate: '2026-10-29', orderId: 'o-101', total: 56400 },
10}));
11

12const { Items } = await db.send(new QueryCommand({
13  TableName: 'Orders',
14  KeyConditionExpression: 'customerId = :c AND begins_with(orderDate, :m)',
15  ExpressionAttributeValues: { ':c': 'c-1', ':m': '2026-10' },
16}));
17console.log(Items);

[ { customerId: 'c-1', orderDate: '2026-10-29', orderId: 'o-101', total: 56400 } ]

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. The document client converts plain JavaScript objects to DynamoDB types.
2. PutCommand writes an item with the full primary key.
3. The query gets one customer’s orders for October 2026 using the sort key prefix.
4. No Scan is needed because the design matches the access pattern.

Real-world use case#

Common mistakes#

Best practices#

• List access patterns first
• Choose high-cardinality partition keys
• Use on-demand capacity until traffic is predictable
• Enable point-in-time recovery

Remember this#

Practice exercise#

1aws dynamodb create-table --table-name Orders \
2  --attribute-definitions AttributeName=customerId,AttributeType=S AttributeName=orderDate,AttributeType=S \
3  --key-schema AttributeName=customerId,KeyType=HASH AttributeName=orderDate,KeyType=RANGE \
4  --billing-mode PAY_PER_REQUEST

Mini quiz#

Want more? Practise all AWS MCQs · AWS interview questions

Related topics#

My notes#

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