/* NOTE: This is Spring JPA and NOT SPRING DATA JPA
* Spring JPA uses EntityManager to handle entity management
* Spring Data JPA uses a layer of abstraction which further simplifies this process
*/
// application.properties
spring.h2.console.enabled=true
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.show-sql=true // this will show the sql equivalence of JPA operations behind the scene in console
// Course.java
@Entity(name="Course") // name of the table which this class will be mapped with
public class Course {
@Id // primary key column
private long id;
@Column(name="name") // name of the column that this attribute will be mapped to
private String name;
@Column(name="author")
private String author;
public Course() {}
public Course(long id, String name, String author) {
super();
this.id = id;
this.name = name;
this.author = author;
}
// setters
// getters
// toString
}
// CourseJpaRepository.java
@Repository
@Transactional
public class CourseJpaRepository {
@PersistenceContext // Alternative to @Autowired
private EntityManager entityManager; // this will be responsible to manage the operations
public void insert(Course course) {
entityManager.merge(course); // .merge() is used to insert
}
public Course findById(long id) {
return entityManager.find(Course.class, id);
}
public void deleteById(long id) { // There is no direct way of deletion. First you need to find the item and remove the object next
Course course = entityManager.find(Course.class, id);
entityManager.remove(course);
}
}
// CourseCommandLineRunner.java that makes sure to run everything on startup
@Component
public class CourseCommandLineRunner implements CommandLineRunner{
@Autowired
private CourseJpaRepository repository;
@Override
public void run(String... args) throws Exception {
// Insert operations
repository.insert(new Course(1, "Learn AWS!", "Udemy"));
repository.insert(new Course(2, "Learn Azure!", "Udemy"));
repository.insert(new Course(3, "Learn GCP!", "Udemy"));
// Delete operation
repository.deleteById(1);
// Read operations
System.out.println(repository.findById(2));
System.out.println(repository.findById(3));
}
}/* NOTE: This is SPRING DATA JPA and NOT SPRING JPA
* While Spring JPA uses EntityManager to handle entity management
* Spring Data JPA uses a layer of abstraction which further simplifies this process
* It extends JpaRepository that helps to run EntityManager behind simple interface without directly using it
*/
// application.properties
spring.h2.console.enabled=true
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.show-sql=true // this will show the sql equivalence of JPA operations behind the scene in console
// Course.java
@Entity(name="Course") // name of the table which this class will be mapped with
public class Course {
@Id // primary key column
private long id;
@Column(name="name") // name of the column that this attribute will be mapped to
private String name;
@Column(name="author")
private String author;
public Course() {}
public Course(long id, String name, String author) {
super();
this.id = id;
this.name = name;
this.author = author;
}
// setters
// getters
// toString
}
// CourseSpringDataJpaRepository.java
public interface CourseSpringDataJpaRepository extends JpaRepository<Course, Long>{
List<Course> findByAuthor(String author); // custom read method signature, findBy...FieldNameFromEntity
List<Course> findByName(String name); // custom read method signature, findBy...FieldNameFromEntity
}
// CourseCommandLineRunner.java that makes sure to run everything on startup
@Component
public class CourseCommandLineRunner implements CommandLineRunner{
@Autowired
private CourseSpringDataJpaRepository repository;
@Override
public void run(String... args) throws Exception {
// Insert operation
repository.save(new Course(1, "Learn AWS !", "Udemy"));
repository.save(new Course(2, "Learn Azure !", "Udemy"));
repository.save(new Course(3, "Learn DevOps !", "Udemy"));
// Delete operation
repository.deleteById(1l);
// Read Operation
System.out.println(repository.findById(2l)); // 2 long type value
System.out.println(repository.findAll());
System.out.println(repository.count());
// Custom read operations
System.out.println(repository.findByAuthor("Udemy"));
System.out.println(repository.findByName("Learn AWS !"));
}
}