JPA/Criteria API - Like & equal problem

Question

I'm trying to use Criteria API in my new project:

public List<Employee> findEmps(String name) {     CriteriaBuilder cb = em.getCriteriaBuilder();     CriteriaQuery<Employee> c = cb.createQuery(Employee.class);     Root<Employee> emp = c.from(Employee.class);     c.select(emp);     c.distinct(emp);     List<Predicate> criteria = new ArrayList<Predicate>();      if (name != null) {         ParameterExpression<String> p = cb.parameter(String.class, "name");         criteria.add(cb.equal(emp.get("name"), p));     }      /* ... */      if (criteria.size() == 0) {         throw new RuntimeException("no criteria");     } else if (criteria.size() == 1) {         c.where(criteria.get(0));     } else {         c.where(cb.and(criteria.toArray(new Predicate[0])));     }      TypedQuery<Employee> q = em.createQuery(c);      if (name != null) {         q.setParameter("name", name);     }      /* ... */      return q.getResultList(); } 

Now when I change this line:

            criteria.add(cb.equal(emp.get("name"), p)); 

to:

            criteria.add(cb.like(emp.get("name"), p)); 

I get an error saying:

The method like(Expression, Expression) in the type CriteriaBuilder is not > applicable for the arguments (Path, ParameterExpression)

What's the problem?

Answer 1

Perhaps you need

criteria.add(cb.like(emp.<String>get("name"), p)); 

because first argument of like() is Expression<String>, not Expression<?> as in equal().

Another approach is to enable generation of the static metamodel (see docs of your JPA implementation) and use typesafe Criteria API:

criteria.add(cb.like(emp.get(Employee_.name), p)); 

(Note that you can't get static metamodel from em.getMetamodel(), you need to generate it by external tools).

Answer 2

Better: predicate (not ParameterExpression), like this :

List<Predicate> predicates = new ArrayList<Predicate>(); if(reference!=null){     Predicate condition = builder.like(root.<String>get("reference"),"%"+reference+"%");     predicates.add(condition); }