Using criteria from JPA

Question

In the new Hibernate use of Criteria is Deprecated . How can I replace such code using org.hibernate.Criteria :

 Criteria criteria = session.createCriteria(Role.class); long id = ((Role) criteria.add(Restrictions.eq("name", name)).uniqueResult()).getId();

to its equivalent using javax.persistence.criteria.CriteriaBuilder from JPA ?

All these criteria are so terrible to be typed in the answers.
Check out whether this site en.wikibooks.org/wiki/Java_Persistence .
I wanted to write a simple service to prepare for an interview with Java Junior.
It is unlikely that I will ever get on it if I read a book on each technology.

Accepted Answer · 2016-11-22T11:49:28

em is an EntityManager instance.

 public Long query(String name) { CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Role> cq = cb.createQuery(Role.class); Root<Role> root = cq.from(Role.class); cq.where(cb.equal(root.get("name"), cb.parameter(String.class, "name"))); // cq.distinct(true); Query q = em.createQuery(cq); q.setParameter("name", name); List<Role> result = q.getResultList(); if (result.size() > 0) { return result.get(0).getId(); } return null; }

In the new hibernate two lines turned into such a big method?
This is a generic implementation that does not depend on Hibernate, but only uses JPA abstractions.
Usually no one writes all these noodles for each request, but makes a wrapper and changes only cq.where .
try {return q.getSingleResult (). getId ()} catch (NoResultException) {return null;
Yes, I agree about unique, but catching Exception is still expensive.

Answer 2 · 2016-11-22T14:38:21

Well, when there is something to copy-paste (thanks, Victor)

 public Long query(String name) { CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Role> cq = cb.createQuery(Role.class); Root<Role> root = cq.from(Role.class); cq.where(cb.equal(root.get("name"), cb.parameter(String.class, "name"))); try { // Тут возможно надо делать приведение типов, // либо вызывать вариант метода, в котором указывается тип возвращаемого параметра // em.createQuery(cq, Role.class)... // либо и так сойдёт return em.createQuery(cq).setParameter("name", name).getSingleResult().getId(); } catch (NoResultException ex) { return null; } }

or

 public Long query(String name) { CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Role> cq = cb.createQuery(Role.class); Root<Role> root = cq.from(Role.class); cq.where(cb.equal(root.get("name"), cb.parameter(String.class, "name"))); List<Role> roles = em.createQuery(cq).setParameter("name", name).getResultList(); return roles.isEmpty() ? null : roles.get(0).getId(); }

Well, that is, a variant of Victor without extra distinct and in places assembled in one line at the expense of the fluent, which is widely used in JPA API.

If you are using static metamodel generation, then root.get ("name") is replaced by root.get (Role_.name). Type safe. Cho. Otherwise on the fig you generally criteria, when there is a text JPQL, and even better than SQL?

SQL is clearly not better if we want to abstract from the syntax of the database.
Although in every joke there is a grain of truth, and a large one.
For example, I often use specific queries: full-text search, recursive cte, which JPA could hardly have planned and will ever be.
As for the abstraction from the database ... But who really needs it.
And the syntax in the part of the JPQL being covered is generally the same for everyone.
Abstraction in the case when you need to maintain multiple databases (yes, it happens).
I myself saw the Chinese product on Delphi, where there is no trace of abstraction (BDE does not count, for even the Chinese did not associate with it).

Using criteria from JPA

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