[JavaEE] JTA, Java Transaction API, Repository for DB opreations

Mainly two things:

1. For all the creating and deleting opreations for the DB, we want to use 'REQUIRED' for the transaction.

2. For all the read only opreations for the DB, we want to use 'SUPPORTS' for the transaction.

package com.pluralsight.bookstore.repository;
 
import com.pluralsight.bookstore.model.Book;
 
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.TypedQuery;
import javax.transaction.Transactional;
import java.util.List;
 
import static javax.transaction.Transactional.TxType.REQUIRED;
import static javax.transaction.Transactional.TxType.SUPPORTS;
 
/**
 * @author Antonio Goncalves
 *         http://www.antoniogoncalves.org
 *         --
 */
 
// For readonly methods we want to using SUPPORTS
@Transactional(SUPPORTS)
public class BookRepository {
 
    // ======================================
    // =          Injection Points          =
    // ======================================
 
    @PersistenceContext(unitName = "bookStorePU")
    private EntityManager em;
 
    // ======================================
    // =          Business methods          =
    // ======================================
 
    public Book find(Long id) {
        return em.find(Book.class, id);
    }
 
    public List<Book> findAll() {
        // For complex SQL, we can also using Query language
        TypedQuery<Book> query = em.createQuery("SELECT b FROM Book b ORDER BY b.title DESC", Book.class);
        return query.getResultList();
    }
 
    public Long countAll() {
        TypedQuery<Long> query = em.createQuery("SELECT COUNT(b) FROM Book b", Long.class);
        return query.getSingleResult();
    }
 
    // For creating and deleting methods, we want to use REQUIRED
    @Transactional(REQUIRED)
    public Book create(Book book) {
        em.persist(book);
        return book;
    }
 
    @Transactional(REQUIRED)
    public void delete(Long id) {
        em.remove(em.getReference(Book.class, id));
    }
}

For the normal (simple) DB opreations, we can see, it uses 'find, persist, remove(getReference)'. Those methods are all from 'EntityManager'. You can think 'EntityMangaer' is a utils service, which can be injected to the Repository to preform operations. In this case, Repository is something similar to 'Effect' (NgRX).

@Transactional(SUPPORTS)
public class BookRepository {
 
    // ======================================
    // =          Injection Points          =
    // ======================================
 
    @PersistenceContext(unitName = "bookStorePU")
    private EntityManager em;
 
    // ======================================
    // =          Business methods          =
    // ======================================
 
    public Book find(Long id) {
        return em.find(Book.class, id);
    }
 
    public List<Book> findAll() {
        // For complex SQL, we can also using Query language
        TypedQuery<Book> query = em.createQuery("SELECT b FROM Book b ORDER BY b.title DESC", Book.class);
        return query.getResultList();
    }
 
    public Long countAll() {
        TypedQuery<Long> query = em.createQuery("SELECT COUNT(b) FROM Book b", Long.class);
        return query.getSingleResult();
    }
 
    // For creating and deleting methods, we want to use REQUIRED
    @Transactional(REQUIRED)
    public Book create(Book book) {
        em.persist(book);
        return book;
    }
 
    @Transactional(REQUIRED)
    public void delete(Long id) {
        em.remove(em.getReference(Book.class, id));
    }
}

Also for some complex SQL operations, we can wirte SQL to query the DB:

    public List<Book> findAll() {
        // For complex SQL, we can also using Query language
        TypedQuery<Book> query = em.createQuery("SELECT b FROM Book b ORDER BY b.title DESC", Book.class);
        return query.getResultList();
    }
 
    public Long countAll() {
        TypedQuery<Long> query = em.createQuery("SELECT COUNT(b) FROM Book b", Long.class);
        return query.getSingleResult();
    }