Role of EntityManager in Spring Data JPA.

What is it?

The core API for interacting with the Persistence Context. While Spring Data JPA abstracts this away via repositories, EntityManager is what actually performs the operations under the hood.

Why use it directly?

1. Dynamic Queries: Using CriteriaBuilder.
2. Bulk Operations: When repository methods are not enough.
3. Flushing: Explicitly synchronizing the persistence context with the database.
4. Native Queries: For complex SQL that doesn't map easily to repositories.