Brief analysis of how to enable MongoDB transactions in SpringBoot

<dependency>
    <groupId></groupId>
    <artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>

=mongodb://localhost:27017,localhost:27018,localhost:27019/mydatabase?replicaSet=rs0
# Or for sharded clusters, connect to the mongos instance# =mongodb://mongos1:27017,mongos2:27017/mydatabase

import ;
import ;
import ;
import ;
import ;
import ; // For example only, non-essential
@Configuration
public class MongoConfig {

    // Spring Boot will automatically configure MongoDatabaseFactory    // You just need to inject it to create MongoTransactionManager    @Bean
    MongoTransactionManager transactionManager(MongoDatabaseFactory dbFactory) {
        return new MongoTransactionManager(dbFactory);
    }

    // Optional: If you also want to configure a MongoTemplate bean    // @Bean
    // public MongoTemplate mongoTemplate(MongoDatabaseFactory dbFactory, MongoClient mongoClient) {
    //     return new MongoTemplate(mongoClient, ().getName());
    // }
}

import ;
import ;
import ; // Spring's transaction annotationimport ; // More general MongoDB exceptionimport ; // Transaction specific exception
@Service
public class AccountService {

    @Autowired
    private AccountRepository accountRepository; // Suppose you have an AccountRepository
    @Autowired
    private AuditLogRepository auditLogRepository; // Suppose you have an AuditLogRepository

    /**
      * Example: Transfer money in a transaction and log logs
      * If any step fails, the entire operation will roll back
      */
    @Transactional // Key notes    public void transferMoney(String fromAccountId, String toAccountId, double amount) {
        try {
            Account fromAccount = (fromAccountId)
                    .orElseThrow(() -> new RuntimeException("Source account not found"));
            Account toAccount = (toAccountId)
                    .orElseThrow(() -> new RuntimeException("Destination account not found"));

            if (() < amount) {
                throw new RuntimeException("Insufficient funds");
            }

            (() - amount);
            (() + amount);

            (fromAccount);

            // Simulate a possible error to test rollback            // if (true) {
            //     throw new RuntimeException("Simulated error during transfer!");
            // }

            (toAccount);

            // Record audit logs            AuditLog log = new AuditLog("Transfer of " + amount + " from " + fromAccountId + " to " + toAccountId);
            (log);

            ("Transfer successful and logged!");

        } catch (RuntimeException e) {
            // @Transactional will automatically roll back when the RuntimeException is thrown            // You can log errors here, but you don't need to rollback manually            ("Transfer failed: " + ());
            throw e; // Rethrow so that Spring can capture and roll back transactions        }
    }

    /**
      * Example: Read-only transaction
      * For operations that only need to read data, it can be marked as read-only, which may have some performance optimizations.
      */
    @Transactional(readOnly = true)
    public Account getAccountDetails(String accountId) {
        return (accountId).orElse(null);
    }

    // Assumptions of entities and repositories    // , 
    //  extends MongoRepository<Account, String>
    //  extends MongoRepository<AuditLog, String>
}

// On the caller or a higher level service@Service
public class TransactionalCallerService {

    @Autowired
    private AccountService accountService;

    private static final int MAX_RETRIES = 3;

    public void performTransferWithRetry(String from, String to, double amount) {
        int retries = 0;
        boolean success = false;
        while (retries < MAX_RETRIES && !success) {
            try {
                (from, to, amount);
                success = true; // If there is no exception, the marking will be successful            } catch (MongoTransactionException e) { //Catch transaction-related exceptions, especially write conflicts                retries++;
                ("Transaction failed due to conflict, retrying (" + retries + "/" + MAX_RETRIES + "): " + ());
                if (retries >= MAX_RETRIES) {
                    ("Max retries reached. Transfer aborted.");
                    throw e; // Or throw a custom business exception                }
                // Consider adding a short delay here                try {
                    (100 * retries); // Simple exponential backoff                } catch (InterruptedException ie) {
                    ().interrupt();
                    throw new RuntimeException("Retry interrupted", ie);
                }
            } catch (RuntimeException e) { //Catch other business logic exceptions                ("Transfer failed due to business error: " + ());
                throw e; // These usually don't need to be tried again            }
        }
    }
}