如何使用JPA使用多重选择查询

Question

I am looking to select multiple items in my DB based on the primary key.

so if I have the name I want to select imagename and refName from the DB.

I found something here http://www.objectdb.com/java/jpa/query/jpql/select

TypedQuery<Object[]> query = em.createQuery(
      "SELECT c.name, c.capital.name FROM Country AS c", Object[].class);
  List<Object[]> results = query.getResultList();
  for (Object[] result : results) {
      System.out.println("Country: " + result[0] + ", Capital: " + result[1]);
  }

Which doesn't work, and someone else seemed to think the code was awfully wrong so I am curious how exactly I will do this?

Thanks all!

Caused by: java.lang.IllegalArgumentException: You have attempted to set a parameter value using a name of i.name that does not exist in the query string SELECT i.name, i.refName, i.imageName FROM Items AS i.
    at org.eclipse.persistence.internal.jpa.QueryImpl.setParameterInternal(QueryImpl.java:928)  at org.eclipse.persistence.internal.jpa.QueryImpl.setParameterInternal(QueryImpl.java:928)
    at org.eclipse.persistence.internal.jpa.EJBQueryImpl.setParameter(EJBQueryImpl.java:593)
    at uploader.AdminControl.fileCreate(AdminControl.java:745)
    at uploader.AdminControl.upload(AdminControl.java:660)
    ... 57 more

..

TypedQuery<Object[]> q = em2.createQuery("SELECT i.name, i.refName, i.imageName FROM Items AS i",Object[].class);
q.setParameter("name", plan.getFace()[i].name);
System.out.println(q);


                            List<Object[]> results = q.getResultList();

                            for (Object[] result : results)
                            {
                            bw.write(result[1].toString());
                            bw.write(result[2].toString());
                            System.out.println("result:" + result[1].toString() + "and" + result[2].toString());
                            }

Answer 1

The problem is because of this code:

q.setParameter("i.name", plan.getFace()[i].name);

Take a look at your JPQL:

SELECT i.name, i.refName, i.imageName FROM Items AS i

You have no parameter named i.name . You should create one that will receive the parameter. Something like

    SELECT i.name, i.refName, i.imageName FROM Items AS i where i.name = :parameterName

And do pass the value:

q.setParameter("parameterName", plan.getFace()[i].name);

Answer 2

The problem is param name

TypedQuery<Object[]> q = em2.createQuery("SELECT i.name, i.refName, i.imageName FROM Items WHERE i.name = :someparam AS i",Object[].class);
q.setParameter("someparam", plan.getFace()[i].name);