本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 在 DynamoDB 中運算存留時間 (TTL)
<a name="time-to-live-ttl-before-you-start"></a>

實作 TTL 的常見方式是依據項目建立或最後更新的時間設定其過期時間。可透過將時間加至 `createdAt` 與 `updatedAt` 時間戳記來完成。例如，新建立的項目可將 TTL 設定為 `createdAt` \$1 90 天。當項目更新時，可將 TTL 重新計算為 `updatedAt` \$1 90 天。

計算出的過期時間必須採用 epoch 格式 (以秒為單位)。要符合過期與刪除條件，TTL 不得早於五年前。如果您使用任何其他格式，TTL 處理程序會忽略該項目。如果您將過期時間設定為您希望項目過期的未來某個時間，則項目會在該時間之後過期。例如，假設您將過期時間設定為 1724241326 （即 2024 年 8 月 21 日星期一 11：55：26 (UTC))。項目會在指定的時間後過期。沒有最短 TTL 持續時間。您可以將過期時間設定為任何未來的時間，例如從目前時間起算 5 分鐘。不過，DynamoDB 通常會在過期時間後 48 小時內刪除過期的項目，而不是在項目過期時立即刪除。

**Topics**
+ [建立項目並設定存留時間](#time-to-live-ttl-before-you-start-create)
+ [更新項目並重新設定存留時間](#time-to-live-ttl-before-you-start-update)

## 建立項目並設定存留時間
<a name="time-to-live-ttl-before-you-start-create"></a>

下列範例示範如何在建立新項目時，使用 `expireAt` 作為 TTL 屬性名稱來計算過期時間。指派語句會將目前時間作為變數取得。在此範例中，過期時間設定為從目前時間起算的 90 天。接著，將時間轉換為 epoch 格式，並以整數型別儲存在 TTL 屬性中。

下列程式碼範例示範如何建立含有 TTL 的項目。

------
#### [ Java ]

**適用於 Java 2.x 的 SDK**  

```
package com.amazon.samplelib.ttl;

import com.amazon.samplelib.CodeSampleUtils;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.model.PutItemRequest;
import software.amazon.awssdk.services.dynamodb.model.PutItemResponse;
import software.amazon.awssdk.services.dynamodb.model.ResourceNotFoundException;

import java.util.HashMap;
import java.util.Map;
import java.util.Optional;

/**
 * Creates an item in a DynamoDB table with TTL attributes.
 * This class demonstrates how to add TTL expiration timestamps to DynamoDB items.
 */
public class CreateTTL {

    private static final String USAGE =
        """
            Usage:
                <tableName> <primaryKey> <sortKey> <region>
            Where:
                tableName - The Amazon DynamoDB table being queried.
                primaryKey - The name of the primary key. Also known as the hash or partition key.
                sortKey - The name of the sort key. Also known as the range attribute.
                region (optional) - The AWS region that the Amazon DynamoDB table is located in. (Default: us-east-1)
            """;
    private static final int DAYS_TO_EXPIRE = 90;
    private static final int SECONDS_PER_DAY = 24 * 60 * 60;
    private static final String PRIMARY_KEY_ATTR = "primaryKey";
    private static final String SORT_KEY_ATTR = "sortKey";
    private static final String CREATION_DATE_ATTR = "creationDate";
    private static final String EXPIRE_AT_ATTR = "expireAt";
    private static final String SUCCESS_MESSAGE = "%s PutItem operation with TTL successful.";
    private static final String TABLE_NOT_FOUND_ERROR = "Error: The Amazon DynamoDB table \"%s\" can't be found.";

    private final DynamoDbClient dynamoDbClient;

    /**
     * Constructs a CreateTTL instance with the specified DynamoDB client.
     *
     * @param dynamoDbClient The DynamoDB client to use
     */
    public CreateTTL(final DynamoDbClient dynamoDbClient) {
        this.dynamoDbClient = dynamoDbClient;
    }

    /**
     * Constructs a CreateTTL with a default DynamoDB client.
     */
    public CreateTTL() {
        this.dynamoDbClient = null;
    }

    /**
     * Main method to demonstrate creating an item with TTL.
     *
     * @param args Command line arguments
     */
    public static void main(final String[] args) {
        try {
            int result = new CreateTTL().processArgs(args);
            System.exit(result);
        } catch (Exception e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }

    /**
     * Process command line arguments and create an item with TTL.
     *
     * @param args Command line arguments
     * @return 0 if successful, non-zero otherwise
     * @throws ResourceNotFoundException If the table doesn't exist
     * @throws DynamoDbException If an error occurs during the operation
     * @throws IllegalArgumentException If arguments are invalid
     */
    public int processArgs(final String[] args) {
        // Argument validation (remove or replace this line when reusing this code)
        CodeSampleUtils.validateArgs(args, new int[] {3, 4}, USAGE);

        final String tableName = args[0];
        final String primaryKey = args[1];
        final String sortKey = args[2];
        final Region region = Optional.ofNullable(args.length > 3 ? args[3] : null)
            .map(Region::of)
            .orElse(Region.US_EAST_1);

        try (DynamoDbClient ddb = dynamoDbClient != null
            ? dynamoDbClient
            : DynamoDbClient.builder().region(region).build()) {
            final CreateTTL createTTL = new CreateTTL(ddb);
            createTTL.createItemWithTTL(tableName, primaryKey, sortKey);
            return 0;
        } catch (Exception e) {
            throw e;
        }
    }

    /**
     * Creates an item in the specified table with TTL attributes.
     *
     * @param tableName The name of the table
     * @param primaryKeyValue The value for the primary key
     * @param sortKeyValue The value for the sort key
     * @return The response from the PutItem operation
     * @throws ResourceNotFoundException If the table doesn't exist
     * @throws DynamoDbException If an error occurs during the operation
     */
    public PutItemResponse createItemWithTTL(
        final String tableName, final String primaryKeyValue, final String sortKeyValue) {
        // Get current time in epoch second format
        final long createDate = System.currentTimeMillis() / 1000;

        // Calculate expiration time 90 days from now in epoch second format
        final long expireDate = createDate + (DAYS_TO_EXPIRE * SECONDS_PER_DAY);

        final Map<String, AttributeValue> itemMap = new HashMap<>();
        itemMap.put(
            PRIMARY_KEY_ATTR, AttributeValue.builder().s(primaryKeyValue).build());
        itemMap.put(SORT_KEY_ATTR, AttributeValue.builder().s(sortKeyValue).build());
        itemMap.put(
            CREATION_DATE_ATTR,
            AttributeValue.builder().n(String.valueOf(createDate)).build());
        itemMap.put(
            EXPIRE_AT_ATTR,
            AttributeValue.builder().n(String.valueOf(expireDate)).build());

        final PutItemRequest request =
            PutItemRequest.builder().tableName(tableName).item(itemMap).build();

        try {
            final PutItemResponse response = dynamoDbClient.putItem(request);
            System.out.println(String.format(SUCCESS_MESSAGE, tableName));
            return response;
        } catch (ResourceNotFoundException e) {
            System.err.format(TABLE_NOT_FOUND_ERROR, tableName);
            throw e;
        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            throw e;
        }
    }
}
```
+  如需 API 的詳細資訊，請參閱《*AWS SDK for Java 2.x API 參考*》中的 [PutItem](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/PutItem)。

------
#### [ JavaScript ]

**適用於 JavaScript (v3) 的 SDK**  

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

export 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, err);
            throw err;
        } else {
            console.log("Item created successfully: %s.", data);
            return data;
        }
    });
}

// Example usage (commented out for testing)
// createDynamoDBItem('your-table-name', 'us-east-1', 'your-partition-key-value', 'your-sort-key-value');
```
+  如需 API 的詳細資訊，請參閱《*適用於 JavaScript 的 AWS SDK API 參考*》中的 [PutItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/PutItemCommand)。

------
#### [ Python ]

**適用於 Python (Boto3) 的 SDK**  

```
from datetime import datetime, timedelta

import boto3


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,
            "expireAt": expiration_time,
        }
        response = table.put_item(Item=item)

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


# Use your own values
create_dynamodb_item(
    "your-table-name", "us-west-2", "your-partition-key-value", "your-sort-key-value"
)
```
+  如需 API 的詳細資訊，請參閱《*適用於 Python (Boto3) 的AWS SDK API 參考*》中的 [PutItem](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/PutItem)。

------

## 更新項目並重新設定存留時間
<a name="time-to-live-ttl-before-you-start-update"></a>

此範例延續自[上一節](#time-to-live-ttl-before-you-start-create)。若項目更新，可重新計算其過期時間。下列範例將 `expireAt` 時間戳記重新計算為自目前時間起的 90 天。

下列程式碼範例示範如何更新項目的 TTL。

------
#### [ Java ]

**適用於 Java 2.x 的 SDK**  
更新資料表中現有 DynamoDB 項目上的 TTL。  

```
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.model.ResourceNotFoundException;
import software.amazon.awssdk.services.dynamodb.model.UpdateItemRequest;
import software.amazon.awssdk.services.dynamodb.model.UpdateItemResponse;

import java.util.HashMap;
import java.util.Map;
import java.util.Optional;

    public UpdateItemResponse updateItemWithTTL(
        final String tableName, final String primaryKeyValue, final String sortKeyValue) {
        // Get current time in epoch second format
        final long currentTime = System.currentTimeMillis() / 1000;

        // Calculate expiration time 90 days from now in epoch second format
        final long expireDate = currentTime + (DAYS_TO_EXPIRE * SECONDS_PER_DAY);

        // Create the key map for the item to update
        final Map<String, AttributeValue> keyMap = new HashMap<>();
        keyMap.put(PRIMARY_KEY_ATTR, AttributeValue.builder().s(primaryKeyValue).build());
        keyMap.put(SORT_KEY_ATTR, AttributeValue.builder().s(sortKeyValue).build());

        // Create the expression attribute values
        final Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();
        expressionAttributeValues.put(
            ":c", AttributeValue.builder().n(String.valueOf(currentTime)).build());
        expressionAttributeValues.put(
            ":e", AttributeValue.builder().n(String.valueOf(expireDate)).build());

        final UpdateItemRequest request = UpdateItemRequest.builder()
            .tableName(tableName)
            .key(keyMap)
            .updateExpression(UPDATE_EXPRESSION)
            .expressionAttributeValues(expressionAttributeValues)
            .build();

        try {
            final UpdateItemResponse response = dynamoDbClient.updateItem(request);
            System.out.println(String.format(SUCCESS_MESSAGE, tableName));
            return response;
        } catch (ResourceNotFoundException e) {
            System.err.format(TABLE_NOT_FOUND_ERROR, tableName);
            throw e;
        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            throw e;
        }
    }
```
+  如需 API 的詳細資訊，請參閱《[AWS SDK for Java 2.x API 參考](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/UpdateItem)》中的 *UpdateItem*。

------
#### [ JavaScript ]

**適用於 JavaScript (v3) 的 SDK**  

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

export const updateItem = async (tableName, partitionKey, sortKey, region = 'us-east-1') => {
    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);

    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;
    }
}

// Example usage (commented out for testing)
// updateItem('your-table-name', 'your-partition-key-value', 'your-sort-key-value');
```
+  如需 API 的詳細資訊，請參閱《[適用於 JavaScript 的 AWS SDK API 參考](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)》中的 *UpdateItem*。

------
#### [ Python ]

**適用於 Python (Boto3) 的 SDK**  

```
from datetime import datetime, timedelta

import boto3


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"
)
```
+  如需 API 的詳細資訊，請參閱《*適用於 Python (Boto3) 的AWS SDK API 參考*》中的 [UpdateItem](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/UpdateItem)。

------

本介紹中的 TTL 範例示範了一種方法，可確保僅保留最近更新的項目於資料表中。更新的項目其存留期會延長，而建立後未更新的項目將在到期後自動刪除，不產生額外成本，有助於減少儲存並維持資料表整潔。