How to Retrieve Old Entity Values in the @HandleBeforeSave Event to Check for Property Changes

How can I access the previous values of an entity in the @HandleBeforeSave event to check if any properties have changed?

@HandleBeforeSave
public void handleBeforeSave(Entity entity) {
    Entity oldEntity = entityManager.find(Entity.class, entity.getId());
    // Compare oldEntity fields with new entity fields
}

In a Java-based application using JPA (Java Persistence API), you can access old entity values during the @HandleBeforeSave event by retrieving the existing entity from the database before saving the new entity. This allows you to compare the current values with previous ones to determine if any properties have changed.

@HandleBeforeSave
public void handleBeforeSave(Entity entity) {
    Entity oldEntity = entityManager.find(Entity.class, entity.getId());
    if (!oldEntity.getProperty().equals(entity.getProperty())) {
        // Property has changed
    }
}

Causes

• Not retrieving the existing entity before saving the new entity.
• Misunderstanding the transaction lifecycle in JPA.
• Failing to implement proper comparison logic between old and new values.

Solutions

• Retrieve the old entity using the entity manager before saving the new one.
• Implement appropriate comparison methods for the entity's properties.
• Log or handle changes accordingly after comparison.

Mistake: Not checking for null values when comparing properties.

Solution: Always check for null to prevent NullPointerExceptions before comparison.

Mistake: Assuming the old entity is automatically available without retrieval.

Solution: Explicitly retrieve the old entity using the entity manager.

Mistake: Inefficient comparison logic that does not account for all properties.

Solution: Use a comprehensive method to compare all relevant properties of the entity.