Release Mew Back to the Wild

What you'll learn

DeleteItem permanently removes an item from the table.
Use ConditionExpression to ensure you delete the correct item.
A common pattern is checking attribute_exists() or matching a version number.
Need an undo button? A soft delete just sets a flag like #status = "Released" (or a TTL timestamp) instead of removing the item.

Section 01

The Delete Operation

DeleteItem is straightforward: give it a key, and the item is gone. However, it is idempotent: if you delete an item that doesn't exist, DynamoDB still returns success!

Section 02

Safe Deletes

To prevent accidents (like deleting a Pokémon that isn't yours, or one that was already transferred), use a ConditionExpression.

Common checks include:

attribute_exists(#name), with #name mapped to Name: Only delete if it actually exists.
#status = :s (with #status mapped to Status): Only delete if status is "Released".
#own = :o (with #own mapped to Owner): Only delete if you are the owner.

Safe Delete ExampleJavaScript

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

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

await docClient.send(new DeleteCommand({
  TableName: "Pokemon",
  Key: { Name: "Mew" },
  ExpressionAttributeNames: { "#name": "Name" },
  ConditionExpression: "attribute_exists(#name)"
}));

Ready · 5 steps · Orbi

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All steps as text

Your app sends DeleteItem to the Pokemon table with Name = "Mew". No condition. Mew was traded to Gary a minute ago.
DynamoDB hashes "Mew" to 416a585c, which routes the request to partition P0.
Your app's write to Mew (Owner Gary) lands on P0 and silently replaces the other change.
This call consumed 1 WCU.
DynamoDB responds with success: Gary's Mew is gone and nobody was warned.

Practice

Your turn

Time to say goodbye to Mew. Use DeleteCommand with a ConditionExpression that only deletes Mew if it exists and still belongs to Ash: attribute_exists(#name) AND #own = :trainer, with #name → Name, #own → Owner (also reserved) and :trainer bound to "Ash".

Use DeleteCommand with a ConditionExpression to remove Mew safely.

// @ts-nocheck
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, DeleteCommand } from "@aws-sdk/lib-dynamodb";
const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);
async function releaseMew() {
  // ⬇️ Delete only if Mew exists and is still owned by Ash.
  const command = new DeleteCommand({
    TableName: "Pokemon",
    Key: {
      Name: "Mew"
    },
    // Add ConditionExpression, ExpressionAttributeNames and Values here
    
  });
  try {
    await docClient.send(command);
    console.log("Mew released safely.");
  } catch (err) {
    console.error("Failed to release Mew:", err instanceof Error ? err.message : String(err));
  }
}

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

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

async function releaseMew() {
  // ⬇️ Delete only if Mew exists and is still owned by Ash.
  const command = new DeleteCommand({
    TableName: "Pokemon",
    Key: {
      Name: "Mew"
    },
    // Add ConditionExpression, ExpressionAttributeNames and Values here
    
  });

  try {
    await docClient.send(command);
    console.log("Mew released safely.");
  } catch (err) {
    console.error("Failed to release Mew:", err instanceof Error ? err.message : String(err));
  }
}

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.

What happens if you run DeleteItem on a key that doesn't exist (without a condition)?

Choose one answer.