If you are manually assigning IDs to entities instead of using @GeneratedValue , you may inadvertently try to reuse an ID that is already present in the table.
To handle these violations gracefully, developers typically employ one of three strategies: If you are manually assigning IDs to entities
Passing a detached entity to the save() method can sometimes lead JPA to treat it as a new record (attempting an INSERT ) rather than an update, causing a primary key collision. If you are manually assigning IDs to entities
Wrap the save logic in a try-catch block specifically for DataIntegrityViolationException . This allows the application to return a user-friendly error message (e.g., "Username already taken") instead of a generic 500 Internal Server Error. If you are manually assigning IDs to entities