In this step by step “tutorial”, I will try to demonstrate how to create a new JSF 2.1 Project and add Primefaces 4.0 to it, alongside with EJB, JPA, REST.
and Ubuntu as OS.
I had a simple Entity with a @oneToMany relationship.
Let’s call the Entity “Store” and the Entity of the relationship “Product”, obviously a Store has many Products.
When it comes to use selectCheckboxMenu with the input (update) of products, a bug arise “org.hibernate.LazyInitializationException: could not initialize proxy – no Session”.
For some reason using the primefaces selectCheckboxMenu (or h:selectmanycheckbox of the slandered JSF components) would end the Session of the current transaction.
to solve this issue I had to supply the type of my collection to the component with attribute name=”collectionType”.
<p:selectCheckboxMenu >
<f:attribute name="collectionType" value="java.util.ArrayList" />
<f:selectItems value="#{bean.getStoreProducts()}"
var="product" itemLabel="#{product.name}"
itemValue="#{product}" />
</p:selectCheckboxMenu>
it depends on your type of List if it’s a Set for example you can use java.util.HashSet instead of java.util.ArrayList.
JPA2 introduced its “Criteria” queries, providing an API for typesafe query generation without the need to hardcode field names etc in queries; it built on the approach of Hibernate Criteria.
In these examples we have two classes, Inventory and Product, where Inventory has a set of products.
Select of persistable objects with simple filter
JPQL single-string would be
SELECT p FROM Product p WHERE p.name = 'MP3 Extra'
JPA Criteria would be
CriteriaQuery criteria = builder.createQuery(Product.class); Root productRoot = criteria.from(Product.class); criteria.select(productRoot); criteria.where(builder.equal(productRoot.get(Product_.name), "MP3 Extra")); List products = em.createQuery(criteria).getResultList();
JPQL single-string would be
SELECT p.value, p.manufacturer FROM Product p WHERE p.name = 'MP3 Extra'
JPA Criteria would be
CriteriaQuery criteria = builder.createQuery(); Root productRoot = criteria.from(Product.class); criteria.multiselect(productRoot.get(Product_.value), productRoot.get(Product_.manufacturer); criteria.where(builder.equal(productRoot.get(Product_.name), "MP3 Extra")); List <Object[]> results = em.createQuery(criteria).getResultList();
Select of aggregate of attribute of persistable objects
JPQL single-string would be
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