Summary

The Spring Data JPA: Refreshing an Entity article discusses the use of the refresh() method to synchronize a JPA entity with its latest database state, particularly in scenarios where concurrent updates may cause the entity to become stale.

Abstract

The article titled Spring Data JPA: Refreshing an Entity delves into the refresh() method provided by the JPA specification. It explains that the primary purpose of this method is to update the state of an entity in the persistence context with the most recent data from the database, ensuring that the entity reflects the latest changes. This is crucial in environments where multiple applications may modify the database simultaneously, leading to potential discrepancies between the entity state and the database records. The article presents a practical use case where an entity becomes outdated during a long-running process, highlighting the importance of using refresh() before making any updates to avoid overwriting concurrent changes. The article concludes by emphasizing the benefits of using refresh() in such scenarios and mentions the possibility of using lock types with the method for additional control over concurrent access.

Opinions

The author suggests that using the refresh() method is a good practice in scenarios where database records might be concurrently updated by other applications.
Refreshing an entity is presented as a logical step to prevent stale data issues, particularly when a long-running process is involved.
The article implies that developers should be aware of the potential for stale entities in the persistence context and should consider using refresh() to mitigate this risk.
It is inferred that the use of refresh() with lock types can be beneficial for managing concurrent access to database records, though the specifics of this approach are not deeply explored in the article.
The author provides a real-world example to illustrate the practicality of the refresh() method, indicating its relevance and utility in everyday development scenarios.

Spring Data JPA: Refreshing an Entity

Understanding Refresh in JPA with Simple Use Case

Introduction

One of the methods provided by JPA specification is refresh(). In this article, we will learn about the refresh method and its use case.

Refresh an Entity

The prime goal of the refresh method is to refresh the state of an instance from the database and overrides the state in the current persistence context so that the current copy becomes the latest.
But the main question is how come our entity in the persistence context become out of sync with the database record?
One of the use cases would be when multiple application writing to the database. Between we read the entity, updating it, and writing it back to the database, there may be some other application that updated some attribute of the database table and immediately our entity in the persistence context becomes stale.
Hence in such cases, it would be a good idea to refresh our entity by loading instances from the database.
We will see one example that demonstrates this scenario.

Use Case

Initial Record in DB

Before running the process permission_id is 2 i.e admin and email is [email protected]

Invoking Target Process

Now we invoked our process that reads the above record from the database.
We are putting a sleep of 20 sec to depict log running logic.
Now we have an account entity in persistence context that we read from the database and next, we are sleeping for 20 secs.

 public void refreshEntityExample() throws InterruptedException {
        Optional<Account> optionalAccount = accountRepository.findByUsername("sam_1234");
        Thread.sleep(20000);
        if(optionalAccount.isPresent()){
            Account loadedFromDB = optionalAccount.get();
            loadedFromDB.setEmail("[email protected]");
            loadedFromDB.setPassword("updated_password_1234");
        }
    }

Meanwhile, we are sleeping there was another process that updated the permission of the record that we have in the persistence context.

    @Transactional
    public void updateAccountEntity() {
        Account account = accountRepository.findByUsername("sam_1234").get();
        Permission editor = permissionRepository.findByType("editor");
        account.setPermission(editor);
    }

Now the loadedFromDB entity becomes out of sync with the database with permission type stale.
after coming out of sleep we updated the email & password of the stale entity and also updated the permission type back to the admin since that is what we have on our entity in the persistence context.

Hence in this scenario, it would be logical to use refresh() loadedFromDB entity before updating and saving it to the database.

public void refreshEntityExample() throws InterruptedException {
        Optional<Account> optionalAccount = accountRepository.findByUsername("sam_1234");
        Thread.sleep(20000);
        if(optionalAccount.isPresent()){
            Account loadedFromDB = optionalAccount.get();
            em.refresh(loadedFromDB);
            loadedFromDB.setEmail("[email protected]");
            loadedFromDB.setPassword("updated_password_1234");
        }
    }

Conclusion

In this article, we learned about refreshing entities before issuing an update command. We also discussed potential use cases when we may use it.
Additionally, We can also pass LockType to the refresh method such as Optimistic or Pessimistic as the second parameter if we want to refresh with lock.

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