Spring-data-jpa-duplicate-key-value-violates-unique-constraint Today

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.

In some cases, using a "query-then-update" approach or custom native queries with ON CONFLICT DO UPDATE (in PostgreSQL) can ensure the operation succeeds regardless of whether the record already exists. Conclusion At the database level, a unique constraint is

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. In some cases, using a "query-then-update" approach or