DynamoDBMapper 和 Table for DynamoDB Tables 有什么区别

Question

在 AWS DynamoDB 中，有两个选项可用于对 Table 进行 CRUD 操作。

DynamoDBMapper : com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;.

    AmazonDynamoDB dbClient = AmazonDynamoDBAsyncClientBuilder.standard().withCredentials(creds)
            .withRegion("us-east-1").build();
    // creds is AWSCredentialsProvider

    DynamoDBMapper mapper = new DynamoDBMapper(dbClient);
    mapper.save(item);

Table: com.amazonaws.services.dynamodbv2.document.Table;.

static DynamoDB dynamoDB =new DynamoDB(dbClient);
Table table = dynamoDB.getTable("TABLE_NAME");
Item item =new Item().withPrimaryKey("","")
        .withString("":, "");
table.putItem(item);

两者似乎做同样的操作。

DynamoDBMapper是Table的一层吗？如果是这样，使用它们中的每一个有什么区别？

Answer 1

如果您想将 Java 类 映射到 DynamoDB tables（这是一个有用的功能），请考虑远离旧的 V1 API（com.amazonaws.services.dynamodbv2 是 V1)。 V2 包是 software.amazon.awssdk.services.dynamodb.*.

用 DynamoDB V2 增强客户端替换这个旧的 API。您可以在这里了解相关信息：

Map items in DynamoDB tables

您可以找到 using the Enhanced Client here 的代码示例。

这是一个 Java V2 代码示例，向您展示了如何使用增强客户端将数据放入 Customer table。如您所见，您可以将 Java Class 映射到 DynamoDB table 中的列，然后在将数据添加到 table.

package com.example.dynamodb;


import software.amazon.awssdk.enhanced.dynamodb.DynamoDbEnhancedClient;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbTable;
import software.amazon.awssdk.enhanced.dynamodb.TableSchema;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSortKey;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbBean;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbPartitionKey;
import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.ZoneOffset;


/*
 * Prior to running this code example, create an Amazon DynamoDB table named Customer with a key named id and populate it with data.
 * Also, ensure that you have setup 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 EnhancedPutItem {

    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();

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

    
    // Puts an item into a DynamoDB table
    public static void putRecord(DynamoDbEnhancedClient enhancedClient) {

        try {
            DynamoDbTable<Customer> custTable = enhancedClient.table("Customer", TableSchema.fromBean(Customer.class));

            // Create an Instant
            LocalDate localDate = LocalDate.parse("2020-04-07");
            LocalDateTime localDateTime = localDate.atStartOfDay();
            Instant instant = localDateTime.toInstant(ZoneOffset.UTC);

            // Populate the Table
            Customer custRecord = new Customer();
            custRecord.setCustName("Susan Blue");
            custRecord.setId("id103");
            custRecord.setEmail("sblue@noserver.com");
            custRecord.setRegistrationDate(instant) ;

            // Put the customer data into a DynamoDB table
            custTable.putItem(custRecord);

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


    @DynamoDbBean
    public static class Customer {

        private String id;
        private String name;
        private String email;
        private Instant regDate;

        @DynamoDbPartitionKey
        public String getId() {
            return this.id;
        };

        public void setId(String id) {

            this.id = id;
        }

        @DynamoDbSortKey
        public String getCustName() {
            return this.name;

        }

        public void setCustName(String name) {

            this.name = name;
        }

        public String getEmail() {
            return this.email;
        }

        public void setEmail(String email) {

            this.email = email;
        }

        public Instant getRegistrationDate() {
            return regDate;
        }
        public void setRegistrationDate(Instant registrationDate) {

            this.regDate = registrationDate;
        }
    }
    
}