Finding the Strongest (Sort Keys)

What you'll learn

Sort Keys automatically organize data within a Partition Key.
Use ScanIndexForward to control ascending or descending order.
A KeyConditionExpression needs an equality test on the partition key (Type1 = :type); the sort key can add =, <, <=, >, >=, BETWEEN, or begins_with (e.g. Attack >= :min).

Section 01

Sort Keys in GSIs

If we set Type1 as the Partition Key and Attack as the Sort Key, DynamoDB automatically keeps our Water-type Pokémon sorted by their Attack power! (Store Attack as a Number: as a String, "105" would sort before "65".) When querying, you can easily fetch the strongest Water Pokémon by reading the items in reverse order.

Query with Sort KeyJavaScript

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

const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);

await docClient.send(new QueryCommand({
  TableName: "JohtoPokemon",
  IndexName: "Type1-Attack-Index",
  KeyConditionExpression: "Type1 = :type",
  ExpressionAttributeValues: { ":type": "water" },
  ScanIndexForward: false // false means descending order (highest attack first!)
}));

Ready · 5 steps · Wick

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All steps as text

Your app sends Query to the Type1-Attack-Index index with Type1 = "fire". ScanIndexForward left at its default (true).
DynamoDB hashes "Fire" to b476151f, which routes the request to partition P3.
P3 returns Cyndaquil (52), Typhlosion (84), Ho-Oh (130).
This call consumed 0.5 RCU.
DynamoDB responds with success: ascending order, so the weakest comes back first.

Practice

Your turn

You want the strongest Fire types first. The GSI Type1-Attack-Index already sorts by Attack — flip the scan direction so the highest Attack comes back at the top.

Add ScanIndexForward: false to return results in descending Attack order.

// @ts-nocheck
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, QueryCommand } from "@aws-sdk/lib-dynamodb";
const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);
async function strongestFireTypes() {
  const command = new QueryCommand({
    TableName: "JohtoPokemon",
    IndexName: "Type1-Attack-Index",
    KeyConditionExpression: "Type1 = :type",
    ExpressionAttributeValues: {
      ":type": "fire",
    },
    // ⬇️ The strongest Pokémon should come first. Add the option that sorts
    //    the sort key (Attack) in DESCENDING order.
  });
  const response = await docClient.send(command);
  console.log("Fire-types, strongest first:", response.Items);
}

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

const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);

async function strongestFireTypes() {
  const command = new QueryCommand({
    TableName: "JohtoPokemon",
    IndexName: "Type1-Attack-Index",
    KeyConditionExpression: "Type1 = :type",
    ExpressionAttributeValues: {
      ":type": "fire",
    },
    // ⬇️ The strongest Pokémon should come first. Add the option that sorts
    //    the sort key (Attack) in DESCENDING order.

  });

  const response = await docClient.send(command);
  console.log("Fire-types, strongest first:", response.Items);
}

Ctrl/⌘ Enter to run · simulated, no AWS callsSimulated — no AWS calls

Check

Check your understanding

Quick Quiz · one question, as many tries as you need.

How do you fetch items in descending order (highest to lowest) using a Query in DynamoDB?

Choose one answer.