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q.setParameter("id", id);
Edition edition = (Edition)q.getSingleResult();
return edition;
Similarly, add methods getSectionById and getArticleById . In order to
create Edition , Section , and Article instances, add methods createEdition ,
createSection , and createArticle . The createEdition method takes Edition
entity properties as arguments. In the createEdition method, create a Edition
object and set the values of the different properties:
Edition edition = new Edition();
Persist the Edition entity object using the persist method of the EntityManager .
The Entity instance data is synchronized with the database when the transaction
with which the entity is associated commits. To synchronize an entity instance with
the database, invoke the flush method, which explicitly commits the transaction.
The flush method also synchronizes the entity data of the associated entities if the
cascade element is set to PERSIST or ALL .
Similarly, in the createSection method, create an instance of Section from the
argument values and persist the Section instance to the database. However, creating
a Section instance is different, because the Section entity has a many-to-one
relationship with the Edition entity. Therefore, we need to add the section to the
associated Edition entity instance. One of the createSection method's parameters is
editionId . Retrieve the Edition entity instance using the getEditionById method:
Edition edition = this.getEditionById(editionId);
Next, merge the state of the Edition entity into the current persistence context using
the merge() method. Without merging the Edition entity instance, we won't be able
to invoke methods on it.
Retrieve a parameterized List of Section entities from the Edition entities using
the getSections method, which we defined in the Edition entity class. To add a
new Section entity to the List , create an ArrayList from the List :
List<Section> sections = edition.getSections();
ArrayList<Section> sectionList =new ArrayList<Section>(sections.
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