Spring JPA interview questions

 

How can you create custom queries in Spring Data JPA?

 Custom queries can be created using:

1.     Query Methods: You can define query methods directly in your repository interface. Spring Data JPA automatically generates the queries based on the method names.

public interface UserRepository extends JpaRepository<User, Long> {

    List<User> findByName(String name);

    List<User> findByEmailContaining(String emailFragment);

}

 

 

 

2.     Query Annotation

Use the @Query annotation to define custom JPQL (Java Persistence Query Language) or SQL queries.

 public interface UserRepository extends JpaRepository<User, Long> {

     @Query("SELECT u FROM User u WHERE u.name = :name")

    List<User> findByName(@Param("name") String name);

     @Query(value = "SELECT * FROM users WHERE email = :email", nativeQuery = true)

    User findByEmail(@Param("email") String email);

}

 

3.     JPQL (Java Persistence Query Language): Use @Query annotation with JPQL for complex queries.

4.     Named Queries

Named queries are predefined JPQL queries that you define using @NamedQuery or @NamedQueries in your entity class.

@Entity

@NamedQuery(name = "User.findByEmail", query = "SELECT u FROM User u WHERE u.email = :email")

public class User {

 

    @Id

    private Long id;

    private String name;

    private String email;

 

    // Getters and setters

}

 

public interface UserRepository extends JpaRepository<User, Long> {

     @Query(name = "User.findByEmail")

    User findByEmail(@Param("email") String email);

}

  

What are the different fetching strategies in JPA?

The fetching strategies are:

EAGER: The related entities are fetched immediately with the parent entity.

LAZY: The related entities are fetched only when accessed, i.e., on demand.