CODEWITHSUNDEEP
javasql-serverswinghibernate
Merim Aliaskarova
Merim Aliaskarova

Reputation: 21

Can't cast the result of query to entity

everyone. I'm new to Hibernate. And I'm making desktop application. I have 2 tables: Worker and Ceh (i.e. Department). Relation between them: many-to-one, i.e. 1 Ceh may contain many workers. I run hql query with inner join to show info about all workers including name of the department and want to show the results in JTable.

The hql query:

private static String query_All_Workers="select W.fio, W.nomer, W.salary, C.name from Worker W Inner Join W.ceh C;

The method that runs query:

   try {
        Session session = HibernateUtil.getSessionFactory().openSession();
        session.beginTransaction();
        Query q = session.createQuery(hql);
        List resultList = q.list();
        displayResult(resultList);
        session.getTransaction().commit();
    } catch (HibernateException he) {
        he.printStackTrace();
    }

The method displayResult(List resultList):

Vector<String> tableHeaders = new Vector<>();
    tableHeaders.add("FIO"); 
    tableHeaders.add("Nomer");
    tableHeaders.add("Salary");
    tableHeaders.add("Ceh");

    Vector tableData = new Vector();
    for(Object o : resultList) {
        Worker worker = (Worker)o;
        Vector<Object> oneRow = new Vector<Object>();
        oneRow.add(worker.getFio());
        oneRow.add(worker.getNomer());
        oneRow.add(worker.getSalary());
        oneRow.add(worker.getCeh());
        tableData.add(oneRow);
    }
    resultTable.setModel(new DefaultTableModel(tableData, tableHeaders));

And the exception occurs like this:

"java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to workers.entity.Worker"

It happens because the list contains objects which are results of inner join query. So I don't know how I can correctly cast the object to Worker entity in order to use its getters.

Upvotes: 0

Views: 2913

Answers (1)

Georgi Mihaylov
Georgi Mihaylov

Reputation: 61

You’re getting the “java.lang.ClassCastException” because you are trying to cast object of type java.lang.Object to custom class Worker:

Worker worker = (Worker)o;

There’s nothing wrong with what you’re trying to do just make sure that the result set returns actually Worker, which is not the case. In your example you are returning resultSet of Objects, because you’re writing regular JDBC select SQL statement.

In order to fix that you will need to checkout Hibernate’s Query Language (HQL) syntax and write HQL query instead of regular JDBC one.

Quick tutorial here http://www.tutorialspoint.com/hibernate/hibernate_query_language.htm

I will advise you do to so from now on, because you will gain the following benefits:

  1. When you write select statements (or any other for that matter) with HQL you think and use Java objects, not DB tables (it helps a lot with table foreign key mappings);
  2. HQL returns whole Java object back since Hibernate will do the necessary conversion for you.

In your case you just need to replace the query_All_Workers with this: “from Worker”. Yup, that’s it! Looks weird but as I said before, Hibernate is taking care of all conversions;

Once you’ve done that, and assuming that your Java class is properly mapped to Hibernate entity, resultSet will contain Workers this time, from which you can easily extract Ceh’s name by using Java getter method: worker.getCeh.getName();

Also using HQL you will not need to make a second select to Ceh table, just to get the name, like you need to do right now.

Hope that helps.

Upvotes: 0

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