与 DynamoDB 配合使用的低级别接口与 DynamoDB 配合使用的文档接口与 DynamoDB 配合使用的对象持久化接口

与 DynamoDB 配合使用的编程接口

每个 Amazon SDK 提供了一个或多个用于使用 Amazon DynamoDB 的编程接口。这些接口范围从简单的低级 DynamoDB 包装到面向对象的持久层。可用接口因您使用的 Amazon SDK 和编程语言而不同。

以下部分重点介绍了一些可用的接口，使用Amazon SDK for Java作为一个示例。（并非所有接口都可用于所有 Amazon SDK。）

主题

与 DynamoDB 配合使用的低级别接口
与 DynamoDB 配合使用的文档接口
与 DynamoDB 配合使用的对象持久化接口

与 DynamoDB 配合使用的低级别接口

每个语言特定 Amazon SDK 为 Amazon DynamoDB 提供了一个低级别接口，其方法与低级别 DynamoDB API 请求非常相似。

在某些情况下，您需要使用数据类型描述符识别数据类型，例如 S 对于字符串，N 对于数字。

注意

一个低级别接口可用于每种特定语言 Amazon SDK。

下面的 Java 程序使用低级别 Amazon SDK for Java 接口。


import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.GetItemRequest;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Before running this Java V2 code example, set up your development
 * environment, including your credentials.
 *
 * For more information, see the following documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 *
 * To get an item from an Amazon DynamoDB table using the AWS SDK for Java V2,
 * its better practice to use the
 * Enhanced Client, see the EnhancedGetItem example.
 */
public class GetItem {
    public static void main(String[] args) {
        final String usage = """

                Usage:
                    <tableName> <key> <keyVal>

                Where:
                    tableName - The Amazon DynamoDB table from which an item is retrieved (for example, Music3).\s
                    key - The key used in the Amazon DynamoDB table (for example, Artist).\s
                    keyval - The key value that represents the item to get (for example, Famous Band).
                """;

        if (args.length != 3) {
            System.out.println(usage);
            System.exit(1);
        }

        String tableName = args[0];
        String key = args[1];
        String keyVal = args[2];
        System.out.format("Retrieving item \"%s\" from \"%s\"\n", keyVal, tableName);
        Region region = Region.US_EAST_1;
        DynamoDbClient ddb = DynamoDbClient.builder()
                .region(region)
                .build();

        getDynamoDBItem(ddb, tableName, key, keyVal);
        ddb.close();
    }

    public static void getDynamoDBItem(DynamoDbClient ddb, String tableName, String key, String keyVal) {
        HashMap<String, AttributeValue> keyToGet = new HashMap<>();
        keyToGet.put(key, AttributeValue.builder()
                .s(keyVal)
                .build());

        GetItemRequest request = GetItemRequest.builder()
                .key(keyToGet)
                .tableName(tableName)
                .build();

        try {
            // If there is no matching item, GetItem does not return any data.
            Map<String, AttributeValue> returnedItem = ddb.getItem(request).item();
            if (returnedItem.isEmpty())
                System.out.format("No item found with the key %s!\n", key);
            else {
                Set<String> keys = returnedItem.keySet();
                System.out.println("Amazon DynamoDB table attributes: \n");
                for (String key1 : keys) {
                    System.out.format("%s: %s\n", key1, returnedItem.get(key1).toString());
                }
            }

        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }
}

与 DynamoDB 配合使用的文档接口

许多 Amazon SDK 提供文档接口，允许您对表和索引执行数据层面操作（创建、读取、更新、删除）。对于文档接口，无需指定数据类型描述符。数据类型由数据本身的语义隐含。这些 Amazon SDK 还提供了一些方法，可以在 JSON 文档转换为 Amazon DynamoDB 本机数据类型之间轻松转换。

注意

适用于 Java、.NET、Node.js 的 Amazon SDK 和 JavaScript SDK 中可用的文档接口。

以下 Java 程序使用 Amazon SDK for Java 的文档接口。程序创建一个 Table 对象，表示 Music 表，然后要求该对象使用 GetItem 检索歌曲。然后程序打印该歌曲的发行年份。

com.amazonaws.services.dynamodbv2.document.DynamoDB 类实施 DynamoDB 文档接口。注意DynamoDB充当一个围绕低级别客户端的包装程序 (AmazonDynamoDB)。


package com.amazonaws.codesamples.gsg;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.GetItemOutcome;
import com.amazonaws.services.dynamodbv2.document.Table;

public class MusicDocumentDemo {

    public static void main(String[] args) {

        AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
        DynamoDB docClient = new DynamoDB(client);

        Table table = docClient.getTable("Music");
        GetItemOutcome outcome = table.getItemOutcome(
                "Artist", "No One You Know",
                "SongTitle", "Call Me Today");

        int year = outcome.getItem().getInt("Year");
        System.out.println("The song was released in " + year);

    }
}

与 DynamoDB 配合使用的对象持久化接口

如果不直接执行数据层面操作，一些 Amazon SDK 提供对象持久化接口。相反，您可以创建表示 Amazon DynamoDB 表和索引中项目的对象，并且仅与这些对象进行交互。这允许您编写以对象为中心的代码，而不是以数据库为中心的代码。

注意

适用于 Java 和 .NET 的 Amazon SDK 提供对象持久化接口。有关更多信息，请参阅 DynamoDB 的用于 DynamoDB 的更高级别编程接口。


import com.example.dynamodb.Customer;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbEnhancedClient;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbTable;
import software.amazon.awssdk.enhanced.dynamodb.Key;
import software.amazon.awssdk.enhanced.dynamodb.TableSchema;
import software.amazon.awssdk.enhanced.dynamodb.model.GetItemEnhancedRequest;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;


import com.example.dynamodb.Customer;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbEnhancedClient;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbTable;
import software.amazon.awssdk.enhanced.dynamodb.Key;
import software.amazon.awssdk.enhanced.dynamodb.TableSchema;
import software.amazon.awssdk.enhanced.dynamodb.model.GetItemEnhancedRequest;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;

/*
 * Before running this code example, create an Amazon DynamoDB table named Customer with these columns:
 *   - id - the id of the record that is the key. Be sure one of the id values is `id101`
 *   - custName - the customer name
 *   - email - the email value
 *   - registrationDate - an instant value when the item was added to the table. These values
 *                        need to be in the form of `YYYY-MM-DDTHH:mm:ssZ`, such as 2022-07-11T00:00:00Z
 *
 * Also, ensure that you have set up your development environment, including your credentials.
 *
 * For information, see this documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */

public class EnhancedGetItem {
    public static void main(String[] args) {
        Region region = Region.US_EAST_1;
        DynamoDbClient ddb = DynamoDbClient.builder()
                .region(region)
                .build();

        DynamoDbEnhancedClient enhancedClient = DynamoDbEnhancedClient.builder()
                .dynamoDbClient(ddb)
                .build();

        getItem(enhancedClient);
        ddb.close();
    }

    public static String getItem(DynamoDbEnhancedClient enhancedClient) {
        Customer result = null;
        try {
            DynamoDbTable<Customer> table = enhancedClient.table("Customer", TableSchema.fromBean(Customer.class));
            Key key = Key.builder()
                    .partitionValue("id101").sortValue("tred@noserver.com")
                    .build();

            // Get the item by using the key.
            result = table.getItem(
                    (GetItemEnhancedRequest.Builder requestBuilder) -> requestBuilder.key(key));
            System.out.println("******* The description value is " + result.getCustName());

        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
        return result.getCustName();
    }
}

Javascript 在您的浏览器中被禁用或不可用。

要使用 Amazon Web Services 文档，必须启用 Javascript。请参阅浏览器的帮助页面以了解相关说明。

DynamoDB 的 Amazon SDK 支持概述

更高级别编程接口