Computing time to live (TTL)

import boto3
from datetime import datetime, timedelta


def create_dynamodb_item(table_name, region, primary_key, sort_key):
    """
    Creates a DynamoDB item with an attached expiry attribute.

    :param table_name: Table name for the boto3 resource to target when creating an item
    :param region: string representing the AWS region. Example: `us-east-1`
    :param primary_key: one attribute known as the partition key.
    :param sort_key: Also known as a range attribute.
    :return: Void (nothing)
    """
    try:
        dynamodb = boto3.resource('dynamodb', region_name=region)
        table = dynamodb.Table(table_name)

        # Get the current time in epoch second format
        current_time = int(datetime.now().timestamp())

        # Calculate the expiration time (90 days from now) in epoch second format
        expiration_time = int((datetime.now() + timedelta(days=90)).timestamp())

        item = {
            'primaryKey': primary_key,
            'sortKey': sort_key,
            'creationDate': current_time,
            'expirationDate': expiration_time
        }

        table.put_item(Item=item)

        print("Item created successfully.")
    except Exception as e:
        print(f"Error creating item: {e}")
        raise


# Use your own values
create_dynamodb_item('your-table-name', 'us-west-2', 'your-partition-key-value', 'your-sort-key-value')

In this request we add logic to compute the expiration time of the newly created item:

import { DynamoDBClient, PutItemCommand } from "@aws-sdk/client-dynamodb";

function createDynamoDBItem(table_name, region, partition_key, sort_key) {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    // Get the current time in epoch second format
    const current_time = Math.floor(new Date().getTime() / 1000);

    // Calculate the expireAt time (90 days from now) in epoch second format
    const expire_at = Math.floor((new Date().getTime() + 90 * 24 * 60 * 60 * 1000) / 1000);

    // Create DynamoDB item
    const item = {
        'partitionKey': {'S': partition_key},
        'sortKey': {'S': sort_key},
        'createdAt': {'N': current_time.toString()},
        'expireAt': {'N': expire_at.toString()}
    };

    const putItemCommand = new PutItemCommand({
        TableName: table_name,
        Item: item,
        ProvisionedThroughput: {
            ReadCapacityUnits: 1,
            WriteCapacityUnits: 1,
        },
    });

    client.send(putItemCommand, function(err, data) {
        if (err) {
            console.log("Exception encountered when creating item %s, here's what happened: ", data, ex);
            throw err;
        } else {
            console.log("Item created successfully: %s.", data);
            return data;
        }
    });
}

// use your own values
createDynamoDBItem('your-table-name', 'us-east-1', 'your-partition-key-value', 'your-sort-key-value');

import boto3
from datetime import datetime, timedelta


def update_dynamodb_item(table_name, region, primary_key, sort_key):
    """
    Update an existing DynamoDB item with a TTL.
    :param table_name: Name of the DynamoDB table
    :param region: AWS Region of the table - example `us-east-1`
    :param primary_key: one attribute known as the partition key.
    :param sort_key: Also known as a range attribute.
    :return: Void (nothing)
    """
    try:
        # Create the DynamoDB resource.
        dynamodb = boto3.resource('dynamodb', region_name=region)
        table = dynamodb.Table(table_name)

        # Get the current time in epoch second format
        current_time = int(datetime.now().timestamp())

        # Calculate the expireAt time (90 days from now) in epoch second format
        expire_at = int((datetime.now() + timedelta(days=90)).timestamp())

        table.update_item(
            Key={
                'partitionKey': primary_key,
                'sortKey': sort_key
            },
            UpdateExpression="set updatedAt=:c, expireAt=:e",
            ExpressionAttributeValues={
                ':c': current_time,
                ':e': expire_at
            },
        )

        print("Item updated successfully.")
    except Exception as e:
        print(f"Error updating item: {e}")


# Replace with your own values
update_dynamodb_item('your-table-name', 'us-west-2', 'your-partition-key-value', 'your-sort-key-value')

The output from the update operation shows that, while the createdAt time is unchanged, the updatedAt and expireAt times have been updated. The expireAt time is now set to 90 days from the time of the last update, which is Thursday, October 19, 2023 at 1:27:15 PM.

import { DynamoDBClient, UpdateItemCommand } from "@aws-sdk/client-dynamodb";
import { marshall, unmarshall } from "@aws-sdk/util-dynamodb";

async function updateDynamoDBItem(tableName, region, partitionKey, sortKey) {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const currentTime = Math.floor(Date.now() / 1000);
    const expireAt = Math.floor((Date.now() + 90 * 24 * 60 * 60 * 1000) / 1000); ////is there a better way to do this?

    const params = {
        TableName: tableName,
        Key: marshall({
            partitionKey: partitionKey,
            sortKey: sortKey
        }),
        UpdateExpression: "SET updatedAt = :c, expireAt = :e",
        ExpressionAttributeValues: marshall({
            ":c": currentTime,
            ":e": expireAt
        }),
    };

    try {
        const data = await client.send(new UpdateItemCommand(params));
        const responseData = unmarshall(data.Attributes);
        console.log("Item updated successfully: %s", responseData);
        return responseData;
    } catch (err) {
        console.error("Error updating item:", err);
        throw err;
    }
}

//enter your values here
updateDynamoDBItem('your-table-name', 'us-east-1', 'your-partition-key-value', 'your-sort-key-value');