Question

我想在DynamoDB中为我的对象实现更改历史记录。这样做的简单方法是指定＆＃34;对象id＆＃34;作为哈希和＆＃34;更新的时间＆＃34;作为范围键。但是，java sdk不允许注释键始终自动生成（在没有注释方便的情况下更改值似乎可行）。为什么呢？

示例代码：

@DynamoDBTable(tableName = "data")
public class Person {

    public static void main(String[] args) {
        AmazonDynamoDBClient client = new AmazonDynamoDBClient()
                .withEndpoint("http://localhost:8000");
        DynamoDBMapper mapper = new DynamoDBMapper(client);

        TableUtils.deleteTableIfExists(client, mapper.generateDeleteTableRequest(Person.class));
        TableUtils.createTableIfNotExists(client, mapper.generateCreateTableRequest(Person.class)
                .withProvisionedThroughput(new ProvisionedThroughput(1L, 1L))
        );

        Person person = new Person();
        person.setPersonId("abc");

        mapper.save(person);
        mapper.save(person);

        TableUtils.deleteTableIfExists(client, mapper.generateDeleteTableRequest(Person.class));
    }

    @DynamoDBHashKey
    private String personId;

    @DynamoDBRangeKey
    @DynamoDBAutoGeneratedTimestamp
    private Long updated;

    public String getPersonId() {
        return personId;
    }

    public void setPersonId(String personId) {
        this.personId = personId;
    }

    public Long getUpdated() {
        return updated;
    }

    public void setUpdated(Long updated) {
        this.updated = updated;
    }
}

例外：

Exception in thread "main" com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: Field com.dynamodb.testpackage.Person[updated] must not have auto-generated key with ALWAYS strategy
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperFieldModel$Builder.build(DynamoDBMapperFieldModel.java:797)
    at com.amazonaws.services.dynamodbv2.datamodeling.StandardModelFactories$SchemaFactory.newTableModel(StandardModelFactories.java:118)
    at com.amazonaws.services.dynamodbv2.datamodeling.StandardModelFactories$SchemaFactory.getTableModel(StandardModelFactories.java:86)
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.getTableModel(DynamoDBMapper.java:401)
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.generateCreateTableRequest(DynamoDBMapper.java:2432)
    at com.dynamodb.testpackage.Person.main(Person.java:21)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Answer 1

您的用例不典型。通常，您不希望更改对象的哈希和范围键。事实上，我会劝阻它。

事实上，对于DynamoDB，项目的唯一特征是它的键（无论是仅分区键还是分区+范围键），因此更改范围键实质上会创建一个新项目，从技术上讲，它不是更新。

我不确定这是否准确表示原因导致SDK中不支持混合@DynamoDBAutoGeneratedTimestamp和@DynamoDBRangeKey，但这肯定是一个原因。

为什么DynamoDB java sdk不允许始终自动生成密钥？

1 个答案: