Topic : JPA Criteria APIKaster Nurmukan

• Powerful Query Capabilities• HQL• Prototypical Use of Query API• Criteria Queries• Prototypical Use of Criteria API• How to use the JPA Criteria API• Examples from simple to complex

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● HQL: The Hibernate Query Language● object-oriented● Criteria API● powerful object model for constructing and executing queries● Query by Example● Not locked in: can perform SQL queries, including stored procedure invocations

● Powerful object-based query language● Hibernate translates HQL to SQL● HQL statements are shorter, more • readable than their SQL counterparts

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• String hql = "from Customer c where c.age > :age";• Query q = session.createQuery();• q.setInteger("age", 33);• q.setFirstResult(20);• q.setMaxResults(10);  // fetch the third page• List customers = q.list(hql);

• ● What makes the Criteria API powerful is• that it allows queries to be specified by • composition.• ● This means that queries can be • constructed dynamically.

• Criteria c = session.createCriteria(Customer.class);• c.add( Restrictions.ilike("name", "Albert%") );• c.addOrder( Order.asc("age") );• c.setMaxResults(20);• c.list();• // entire sequence of calls can also be chained, • // like so:• session.createCriteria(Customer.class).•   add( Restrictions.ilike("name", "Albert%") ).•   addOrder( Order.asc("age") ).•   setMaxResults(20).•   list();

• JQL seems like a great way to leverage your existing SQL JQL seems like a great way to leverage your existing SQL knowledgeknowledge

• no compile time checkingno compile time checking• JPA Criteria API quiet a productivity drain with developers quiet a productivity drain with developers

having to correcthaving to correct, compile and redeploy to  continue.

• CriteriaBuilder cb = em.getCriteriaBuilder();• CriteriaQuery cqry = em.createQuery();

 CriteriaBuilder cb = em.getCriteriaBuilder(); //Step 1           

 CriteriaQuery cqry = em.createQuery(); //Step 1•   //Interesting stuff happens here•  Root<MyEntity> root = cqry.from(MyEntity.class); //Step 2•              cqry.select(root); Step 3•              •              ….•  Query qry = em.createQuery(cqry); //Step 6  List<MyEnity> results = qry.getResultList(); //Step 6

•  Root<MyEntity> root = cqry.from(MyEntity.class); //Step 2•    cqry.select(root); //Step 3•  Predicate pGtAge = cb.gt(root.get("age"),10); //Step 4•      cqry.where(pGtAge); //Step 5

 Root<MyEnity> root = cqry.from(MyEntity.class); //Step 2•      cqry.select(root); //Step 3•      Predicate pGtAge = cb.gt(root.get("age"),10); //Step 4•      Predicate pGtDateCreated=•   cb.greaterThan(root.get("dateCreated"),date); //Step 4 Predicate pAnd = cb.and(pGtDateCreated,pGtAge); //Step 4

•     cqry.where(pAnd); //Step 5

•              //assume we have created a date object for 2011-07-01 •             //called date•              Root<MyEnity> root = cqry.from(MyEntity.class); //Step 2•              cqry.select(root); //Step 3•              Predicate pGtAge = cb.gt(root.get(MyEntity_.age),10); //Step 4•              Predicate pGtDateCreated=•                cb.greaterThan(root.get(MyEntity_.dateCreated),date); //Step 4•              Predicate pAnd = cb.and(pGtDateCreated,pGtAge); //Step 4•              cqry.where(pAnd); //Step 5

•              Root<MyEnity> root = cqry.from(MyEntity.class); //Step 2•              Join<MyEntity,AnotherEntity> join =•                              root.join(MyEntity_.anotherEntity); //Step 2•             //Join<MyEntity,AnotherEntity> join =•                              root.join("anotherEntity"); //Step 2•  •              cqry.select(root); //Step 3•              Predicate pGtAge = cb.gt(root.get(MyEntity_.age),10); //Step 4•              Predicate pGtDateCreated=•                              cb.greaterThan(root.get(MyEntity_.dateCreated),date); //Step 4•              Predicate pEqEnabled = cb.equals(join.get(AnotherEntity_.enabled),false);•              Predicate pAnd = cb.and(pGtDateCreated,pGtAge,pEqEnabled); //Step 4•              cqry.where(pAnd); //Step 5

• Root<MyEnity> root = cqry.from(MyEntity.class); //Step 2•              cqry.select(root.get(MyEntity_.dateCreated)); //Step 3•  • If we wanted to use an aggregate function and get the minimum dateCreated we could

use something like:•  •  •              Root<MyEnity> root = cqry.from(MyEntity.class); //Step 2•              Expression min =•                       cb.min(root.get(MyEntity_.dateCreated));//Step3•              cqry.select(min); //Step 3

• http://www.oracle.com• http://www.jumpingbean.co.za/blogs/jpa2-criteria-api