從讀取作業中篩選過期的項目有條件地寫入過期的項目在 DynamoDB Streams 中識別已刪除的項目

使用過期的物品

可以從讀取和寫入作業中篩選擱置刪除的過期項目。這在過期的數據不再有效且不應該被使用的情況下很有用。如果未篩選它們，它們將繼續顯示在讀取和寫入作業中，直到背景處理程序將它們刪除為止。

注意

這些項目仍會計入儲存和讀取成本，直到它們被刪除為止。

TTL 刪除可以在 DynamoDB Streams 中識別，但只能在發生刪除的區域中識別。複寫至全域資料表區域的 TTL 刪除作業在刪除複寫目標區域的 DynamoDB 串流中無法識別。

從讀取作業中篩選過期的項目

對於掃描和查詢等讀取作業，篩選器運算式可以篩選出擱置刪除的過期項目。如下列程式碼片段所示，篩選器運算式可以篩選出 TTL 時間等於或小於目前時間的項目。這是通過一個賦值語句來完成的，該語句將當前時間作為一個變量（now），該變量被轉換int為 epoch 時間格式。

Python


import boto3
from datetime import datetime


def query_dynamodb_items(table_name, partition_key):
    """

    :param table_name: Name of the DynamoDB table
    :param partition_key:
    :return:
    """
    try:
        # Initialize a DynamoDB resource
        dynamodb = boto3.resource('dynamodb',
                                  region_name='us-east-1')

        # Specify your table
        table = dynamodb.Table(table_name)

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

        # Perform the query operation with a filter expression to exclude expired items
        # response = table.query(
        #    KeyConditionExpression=boto3.dynamodb.conditions.Key('partitionKey').eq(partition_key),
        #    FilterExpression=boto3.dynamodb.conditions.Attr('expireAt').gt(current_time)
        # )
        response = table.query(
            KeyConditionExpression=dynamodb.conditions.Key('partitionKey').eq(partition_key),
            FilterExpression=dynamodb.conditions.Attr('expireAt').gt(current_time)
        )

        # Print the items that are not expired
        for item in response['Items']:
            print(item)

    except Exception as e:
        print(f"Error querying items: {e}")


# Call the function with your values
query_dynamodb_items('Music', 'your-partition-key-value')

更新操作的輸出顯示，雖然createdAt時間不變，但updatedAt和expireAt時間已更新。現在expireAt時間設定為上次更新時間起 90 天，即 2023 年 10 月 19 日（星期四）下午 1:27：15。

partition_key	createdAt	updatedAt	到期時間	屬性 _1	屬性 _2
某些值	2023-07-17 14:11:05.322 323	2023-07-19 13:27:15.213 423	1697722035	new_value	某些值

Javascript


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

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

    const currentTime = Math.floor(Date.now() / 1000);

    const params = {
        TableName: tableName,
        KeyConditionExpression: "#pk = :pk",
        FilterExpression: "#ea > :ea",
        ExpressionAttributeNames: {
            "#pk": "primaryKey",
            "#ea": "expireAt"
        },
        ExpressionAttributeValues: marshall({
            ":pk": primaryKey,
            ":ea": currentTime
        })
    };

    try {
        const { Items } = await client.send(new QueryCommand(params));
        Items.forEach(item => {
            console.log(unmarshall(item))
        });
        return Items;
    } catch (err) {
        console.error(`Error querying items: ${err}`);
        throw err;
    }
}

//enter your own values here
queryDynamoDBItems('your-table-name', 'your-partition-key-value');

有條件地寫入過期的項目

條件運算式可用來避免對過期項目進行寫入。下面的代碼片段是條件式更新，用於檢查到期時間是否大於當前時間。如果為 true，寫入操作將繼續。

Python


import boto3
from datetime import datetime, timedelta
from botocore.exceptions import ClientError


def update_dynamodb_item(table_name, region, primary_key, sort_key, ttl_attribute):
    """
    Updates an existing record in a DynamoDB table with a new or updated TTL attribute.

    :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.
    :param ttl_attribute: name of the TTL attribute in the target DynamoDB table
    :return:
    """
    try:
        dynamodb = boto3.resource('dynamodb', region_name=region)
        table = dynamodb.Table(table_name)

        # Generate updated TTL in epoch second format
        updated_expiration_time = int((datetime.now() + timedelta(days=90)).timestamp())

        # Define the update expression for adding/updating a new attribute
        update_expression = "SET newAttribute = :val1"

        # Define the condition expression for checking if 'ttlExpirationDate' is not expired
        condition_expression = "ttlExpirationDate > :val2"

        # Define the expression attribute values
        expression_attribute_values = {
            ':val1': ttl_attribute,
            ':val2': updated_expiration_time
        }

        response = table.update_item(
            Key={
                'primaryKey': primary_key,
                'sortKey': sort_key
            },
            UpdateExpression=update_expression,
            ConditionExpression=condition_expression,
            ExpressionAttributeValues=expression_attribute_values
        )

        print("Item updated successfully.")
        return response['ResponseMetadata']['HTTPStatusCode']  # Ideally a 200 OK
    except ClientError as e:
        if e.response['Error']['Code'] == "ConditionalCheckFailedException":
            print("Condition check failed: Item's 'ttlExpirationDate' is expired.")
        else:
            print(f"Error updating item: {e}")
    except Exception as e:
        print(f"Error updating item: {e}")


# replace with your values
update_dynamodb_item('your-table-name', 'us-east-1', 'your-partition-key-value', 'your-sort-key-value',
                     'your-ttl-attribute-value')

partition_key	createdAt	updatedAt	到期時間	屬性 _1	屬性 _2
某些值	2023-07-17 14:11:05.322 323	2023-07-19 13:27:15.213 423	1697722035	new_value	某些值

Javascript


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


// Example function to update an item in a DynamoDB table.
//  The function should take the table name, region, partition key, sort key, and new attribute as arguments.
//  The function should use the DynamoDB client to update the item.
//  The function should return the updated item.
//  The function should handle errors and exceptions.
const updateDynamoDBItem = async (tableName, region, partitionKey, sortKey, newAttribute) => {
    const client = new DynamoDBClient({
        region: region,
        endpoint: `https://dynamodb.${region}.amazonaws.com`
    });

    const currentTime = Math.floor(Date.now() / 1000);

    const params = {
        TableName: tableName,
        Key: marshall({
            artist: partitionKey,
            album: sortKey
        }),
        UpdateExpression: "SET newAttribute = :newAttribute",
        ConditionExpression: "expireAt > :expiration",
        ExpressionAttributeValues: marshall({
            ':newAttribute': newAttribute,
            ':expiration': currentTime
        }),
        ReturnValues: "ALL_NEW"
    };

    try {
        const response = await client.send(new UpdateItemCommand(params));
        const responseData = unmarshall(response.Attributes);
        console.log("Item updated successfully: ", responseData);
        return responseData;
    } catch (error) {
        if (error.name === "ConditionalCheckFailedException") {
            console.log("Condition check failed: Item's 'expireAt' is expired.");
        } else {
            console.error("Error updating item: ", error);
        }
        throw error;
    }
};

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

在 DynamoDB Streams 中識別已刪除的項目

串流紀錄包含使用者身分欄位 Records[<index>].userIdentity。由 TTL 程序刪除的項目具有下列欄位：


Records[<index>].userIdentity.type
"Service"

Records[<index>].userIdentity.principalId
"dynamodb.amazonaws.com"

下列 JSON 會顯示單一串流記錄的相關部分：


"Records": [ 
  { 
	... 
		"userIdentity": {
		"type": "Service", 
      	"principalId": "dynamodb.amazonaws.com" 
   	} 
   ... 
	} 
]

您的瀏覽器已停用或無法使用 Javascript。

您必須啟用 Javascript，才能使用 AWS 文件。請參閱您的瀏覽器說明頁以取得說明。

文件慣用形式

計算 TTL

使用項目：Java