使用 DynamoDBMapper 进行条件更新操作

DynamoDBMapperConfig config = new DynamoDBMapperConfig(DynamoDBMapperConfig.SaveBehavior.UPDATE);
DynamoDBMapper mapper = new DynamoDBMapper(dynamoDBClient, config);

@DynamoDBTable(tableName = "Account")
public class Account {
    @DynamoDBHashKey(attributeName = "accountId")
    private String accountId;

    @DynamoDBAttribute(attributeName = "balance")
    private Double balance;

    // Getters and setters
    public String getAccountId() { return accountId; }
    public void setAccountId(String accountId) { this.accountId = accountId; }
    public Double getBalance() { return balance; }
    public void setBalance(Double balance) { this.balance = balance; }
}

public class AccountService {

    private final DynamoDBMapper mapper;

    public AccountService(AmazonDynamoDB client) {
        DynamoDBMapperConfig config = new DynamoDBMapperConfig(DynamoDBMapperConfig.SaveBehavior.UPDATE);
        this.mapper = new DynamoDBMapper(client, config);
    }

    public void decrementBalance(String accountId, double amount) {
        Account account = mapper.load(Account.class, accountId);
        if (account != null) {
            account.setBalance(account.getBalance() - amount);
            mapper.save(account);
        } else {
            // Handle account not found scenario
            System.out.println("Account not found: " + accountId);
        }
    }
}