Spring Hibernate: Fixing Join Table Row Deletion Issue When Updating Many-to-Many Relationships

Working with Hibernate and Spring in Java applications is often straightforward, but problems can crop up, especially when handling many-to-many relationships. A notorious issue among developers is when updating related entities—old rows in join tables aren’t always automatically deleted. Imagine replacing actors in a “Movie” entity in your database, only to discover that previous actor records are lingering behind in a join table. Such scenarios are common hurdles, creating unwanted data and inconsistencies.

Understanding the Many-to-Many Relationship: Movies and Actors

Consider a movie database. Typically, we’ll have two primary entities: Movie and Actor. Each movie can feature multiple actors, and actors can act across multiple movies—clearly a many-to-many scenario.

To represent such relationships, developers often introduce a third table—known as a join table. In our case, we might call it MovieActor. This table comprises primarily two columns referencing the primary keys of Movie and Actor:

• movie_id
• actor_id

When Hibernate manages this association, things can become tricky, particularly regarding updates and deletions within the join table.

Visualizing the Problem

Suppose initially we have a movie entry titled “The Matrix,” which has two actors: Keanu Reeves and Laurence Fishburne. The join table (MovieActor) initially looks like this:

Now we want to update the actors, replacing them with two new actors: Carrie-Anne Moss and Hugo Weaving. We anticipate seeing this after the update:

But often, what you actually see is different—rows for the original actors might still remain in the join table. Why does this happen?

Hibernate’s Behavior with Many-to-Many Relationships

Hibernate generally manages entity associations effectively. But in many-to-many relationships, its default behavior might not align with every developer’s expectation. Specifically, Hibernate is efficient at adding new relationships, but it isn’t always great at deleting old ones automatically.

Often, when you replace collection-based associations, Hibernate may ignore removals if not explicitly instructed to delete outdated join records. This results in redundant, orphaned data lingering behind, complicating your database cleanup efforts.

How Your Hibernate Entity Classes Might Look

Here’s a quick glance at how these entities typically appear:

Movie Entity:

@Entity
@Table(name = "movie")
public class Movie {
    @Id
    private Long id;
    private String title;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(
        name = "MovieActor",
        joinColumns = @JoinColumn(name = "movie_id"),
        inverseJoinColumns = @JoinColumn(name = "actor_id")
    )
    private Set<Actor> actors = new HashSet<>();
    // getters and setters
}

Actor Entity:

@Entity
@Table(name = "actor")
public class Actor {
    @Id
    private Long id;
    private String name;

    @ManyToMany(mappedBy = "actors")
    private Set<Movie> movies = new HashSet<>();
    // getters and setters
}

Here, the @ManyToMany annotation creates and manages the relationship. When entities on either side are updated, Hibernate handles persistence automatically. But it doesn’t always handle deletions as intuitively, especially during updates.

Implementing a Service Method to Update Actors

Let’s say we have a service method that updates the actor list for a specified movie:

public void updateMovieActors(Long movieId, List<Actor> newActors){
    Movie movie = movieRepository.findById(movieId);
    
    // clear previous actors
    movie.getActors().clear();

    // add new actors
    for(Actor actor : newActors){
        movie.getActors().add(actor);
    }

    movieRepository.save(movie);
}

It seems sufficient at first glance: clear existing actors, add new ones, and save. But here’s the catch—this often fails to delete rows directly from the MovieActor join table.

Why Does Deletion Fail?

Hibernate performs the “clear()” call only on the in-memory collection associated with your entity. Without specifying certain operations explicitly, it doesn’t necessarily propagate deletes down to the database. Typically, Hibernate sees this as merely breaking the relationships, not necessarily removing orphaned join rows.

To solve this precisely, you usually need extra logic that explicitly deletes join table entries or proper handling of orphan removal.

Tackling the Deletion Issue: Alternative Approaches

Here are a few strategies you can implement:

• Explicitly Deleting Join Rows: Create custom methods using native queries or the Criteria API explicitly to remove outdated join entries.
• Use OrphanRemoval: Hibernate provides the orphanRemoval=true attribute to automatically handle these cases. However, note that orphan removal’s behavior might not always work with many-to-many mappings. Usually, this works best when you break the join entity into explicit entities (many-to-one relations).
• Using Bidirectional Relationships: Ensuring that relationships are bidirectional and properly synced on both sides sometimes helps Hibernate recognize deletions correctly.

For instance, explicitly deleting old join rows before adding new relationships could look like this:

@Query("DELETE FROM MovieActor ma WHERE ma.movie.id = :movieId")
void deleteOldActorRelations(@Param("movieId") Long movieId);

After calling this method, you’d re-add new actors and persist smoothly.

Testing and Validating Your Fix

After revising your deletion logic, it’s vital to test thoroughly. Here’s a simple checklist:

• Insert initial related entities (Movies, Actors, Join rows).
• Run your actor update logic.
• Query and verify the join table records to ensure old association entries are deleted.
• Repeat this with various edge cases to ensure robustness.

Always ensure changes are reflected both in-memory and actual database tables—use tools like MySQL Workbench or pgAdmin for visual verification.

Optimizing Hibernate: A Practical Necessity

Handling relationship updates smoothly in Spring and Hibernate can seem cumbersome initially. But understanding clearly how Hibernate operates—like its quirks in many-to-many associations—can save considerable time.

With careful consideration and proper handling, you can craft efficient, consistent, and maintainable database interaction logic that works seamlessly.

Have you faced similar Hibernate issues recently? What methods did you try, and what has worked best for you? Join the discussion or share your thoughts below.