In a multi-threaded environment, two processes might check if a value (like an email address) exists at the same time. Both see that it doesn’t, both attempt to insert it, and the second one fails.
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. In a multi-threaded environment, two processes might check
At the database level, a unique constraint is a fail-safe that ensures data integrity. When Spring Data JPA’s save() or saveAndFlush() method is called, the underlying Hibernate provider generates an INSERT or UPDATE statement. If the database engine (such as PostgreSQL or MySQL) detects that the new data conflicts with an existing entry, it rejects the transaction and throws a low-level error. At the database level, a unique constraint is
Spring then catches this vendor-specific SQL exception and wraps it in a DataIntegrityViolationException . This abstraction is helpful for maintaining database-agnostic code, but it requires the developer to look at the "Root Cause" in the stack trace to identify which specific constraint was violated. Common Triggers in Spring Data JPA Spring then catches this vendor-specific SQL exception and