How to prevent ClassCastException with JPA entities?

Question

I get a ClassCastException when trying to query my JPA entity class. I only want json to show two columns. That is name and address. How do I only show selected columns in JPA? From debugging it has to be the for loop. So List is the object and I need to make the right side an object instead of a list correct?

Entity

@Entity
@Table(name = "Personnel")
public class User implements Serializable {

private String id;
private String name;
private String address;

public User(String id, String name, String address) 
{
this.id = id;
this.name = name;
this.address = address;
}

@Id
@Column(name = "name", unique = true, nullable = false)
public String getName() {
    return this.name;
}....
 //setters getters

Query/Impl

public List<User> getRecords(User ent){

     String sql = "select "
                + " usr.name, usr.address "                 
                + " from User usr"           
                + " where usr.id = '1' ";

    List<User> records = this.getSession().createQuery(sql).list();
    for ( User event : records ) {
        System.out.println( "Records (" + event.getName + ") );
    }

    return records;
 }

Update

This is my attempt to declare the result object as List. Does the method have to be an object instead of ?

public List<User> getRecords(User ent){
     String sql = "select "
                + " usr.name, usr.address "                 
                + " from User usr"           
                + " where usr.id = '1' ";

       Map<String, String> results = new HashMap<String, String>();
       List<Object[]> resultList = this.getSession().createQuery(sql).list();

       // Place results in map
       for (Object[] items: resultList) {
          results.put((String)items[0], (String)items[1]);
          results.toString();
       }
       return (List<User>) results;

Try `List records = (List)this.getSession().createQuery(sql).list();` — karim mohsen, Aug 16 '15 at 11:59
I'm not sure if I understand your problem, but... [SQL Transformers](http://stackoverflow.com/a/3937519/2387977) may help you. — Dherik, Aug 16 '15 at 13:37

Vlad Mihalcea · Answer 1 · 2021-01-08T16:28:43.920

1

You can pass a DTO class to the SELECT clause like this:

List<UserDTO> resultList = this.getSession().createQuery("""
    select
        new my.package.UserDTO(usr.name, usr.address)
    from User usr
    where usr.id = :userId
    """)
.setParameter("userId", userId)
.getResultList();

edited Jan 08 '21 at 16:28

answered Aug 16 '15 at 14:58

Vlad Mihalcea

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score 0 · Answer 2 · answered Aug 16 '15 at 11:24

0

You should read the complete object:

String sql = " from User usr"           
            + " where usr.id = '1' ";

Or declare the result object as List<Object[]>

answered Aug 16 '15 at 11:24

Jens

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Jens, reading the complete object works fine. Thanks. However I need to get specific columns so I'm attempting to declare the result object as List – Sunny Aug 16 '15 at 12:27
@Sunny You can also use the List as return type. But you have to map it by your own. – Jens Aug 16 '15 at 17:05

score 0 · Answer 3 · answered Aug 16 '15 at 11:35

0

You can use generic(I assure you are using java 1.5 and above) and and one you get result, you do type check and downcast to desired type.

answered Aug 16 '15 at 11:35

java_bee

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score 0 · Answer 4 · edited May 23 '17 at 12:06

0

If You don't want to read the complete object you have to use Criteria and Projection on specific properties.

See this answer it will help

edited May 23 '17 at 12:06

Community

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answered Aug 16 '15 at 13:44

karim mohsen

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How to prevent ClassCastException with JPA entities?

4 Answers4