Category category2 = new Category();
category2.setTitle("Littérature");
entityManager.persist(category2);
Author author1 = new Author();
author1.setFirstName("Michel");
author1.setLastName("Martin");
entityManager.persist(author1);
Author author2 = new Author();
author2.setFirstName("Christian");
author2.setLastName("Bauer");
entityManager.persist(author2);
Author author3 = new Author();
author3.setFirstName("J-K");
author3.setLastName("Rowling");
entityManager.persist(author3);
Book book = new Book();
book.setTitle("HTML 5 et CSS 3");
book.setCategory(category1);