using a ParameterExpression versus a variable in JPA Criteria API

Question

When using the JPA Criteria API, what is the advantage of using a ParameterExpression over a variable directly? E.g. when I wish to search for a customer by name in a String variable, I could write something like

private List<Customer> findCustomer(String name) {
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Customer> criteriaQuery = cb.createQuery(Customer.class);
    Root<Customer> customer = criteriaQuery.from(Customer.class);
    criteriaQuery.select(customer).where(cb.equal(customer.get("name"), name));
    return em.createQuery(criteriaQuery).getResultList();
}

With parameters this becomes:

private List<Customer> findCustomerWithParam(String name) {
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Customer> criteriaQuery = cb.createQuery(Customer.class);
    Root<Customer> customer = criteriaQuery.from(Customer.class);
    ParameterExpression<String> nameParameter = cb.parameter(String.class, "name");
    criteriaQuery.select(customer).where(cb.equal(customer.get("name"), nameParameter));
    return em.createQuery(criteriaQuery).setParameter("name", name).getResultList();
}

For conciseness I would prefer the first way, especially when the query gets longer with optional parameters. Are there any disadvantages of using parameters like this, like SQL injection?

Answer 1

you can use ParameterExpression like this: assume that you have some input filter, an example could be this:

• in your query you have to check the value of a fiscal Code.

let's start: first of all create criteriaQuery and criteriaBuilder and root

        CriteriaBuilder cb = _em.getCriteriaBuilder();
        CriteriaQuery<Tuple> cq = cb.createTupleQuery();
        Root<RootEntity> soggettoRoot = cq.from(RootEntity.class);

1) inizialize a predicateList(use for where clause) and a paramList(use for param)

Map<ParameterExpression,String> paramList = new HashMap();
List<Predicate> predicateList = new ArrayList<>();

2 )check if the input is null and create predicateList and param

if( input.getFilterCF() != null){
            //create ParameterExpression
            ParameterExpression<String> cf = cb.parameter(String.class);


           //if like clause
            predicateList.add(cb.like(root.<String>get("cf"), cf));
            paramList.put(cf , input.getFilterCF() + "%");

           //if equals clause
           //predicateList.add(cb.equal(root.get("cf"), cf));   
           //paramList.put(cf,input.getFilterCF()());
        }

3) create the where clause

 cq.where(cb.and(predicateList.toArray(new   Predicate[predicateList.size()])));
TypedQuery<Tuple> q = _em.createQuery(cq);

4) set param value

        for(Map.Entry<ParameterExpression,String> entry : paramList.entrySet())
        {
            q.setParameter(entry.getKey(), entry.getValue());
        }