Getting a ClassCastException when trying a join query in Hibernate-CodePudding

This is my tables:

@Entity

@Table(name="Students") public class Students {

@Id
@Column(name="Student_ID")
private int id;

@Column(name="Student_Name")
private String name;

@Column(name="Email_ID")
private String emailId;

@Column(name="Phone_no")
private long phoneNo;

@Column(name="Class_ID")
private int classId;

@Column(name="DOB")
private Date dob;

and

@Entity

@Table(name="Assigned") public class Assign {

@Id
@Column(name="Assign_ID")
private int aId;

@Column(name="Class_ID")
private int classId;

@Column(name="Teacher_ID")
private int tId;

@Column(name="Subject_ID")
private int sId;

When I run this code :

PrintWriter out = response.getWriter();
    out.append("<html><body>");

    SessionFactory sf = HibernateUtil.getSessionFactory();

    Session session = sf.openSession();
    
    List<Subjects> subjects = session.createQuery(" from Subjects").list();
    
    out.println("<h1> Students List :-");
    out.println("<table>");
    
    out.println("<tr>");
    out.println("<th> Subject Id </th>");
    out.println("<th> Subject Name </th>");
    out.println("</tr>");
    
    for(Subjects subject : subjects ) {
        out.println("<tr>");
        out.println("<td>" subject.getsId() "</td>");
        out.println("<td>" subject.getsName() "</td>");
        out.println("</tr>");
    }
    out.println("</table>");
    out.append("</body></html>");

It works just fine But when I try to run this:

PrintWriter out = response.getWriter();
    out.append("<html><body>");

    SessionFactory sf = HibernateUtil.getSessionFactory();

    Session session = sf.openSession();
    
    List<Subjects> subjects = session.createQuery("from Subjects s, Assign a where s.sId = a.sId and a.classId = 2").list();
    
    out.println("<h1> Students List :-");
    out.println("<table>");
    
    out.println("<tr>");
    out.println("<th> Subject Id </th>");
    out.println("<th> Subject Name </th>");
    out.println("</tr>");
    
    for(Subjects subject : subjects ) {
        out.println("<tr>");
        out.println("<td>" subject.getsId() "</td>");
        out.println("<td>" subject.getsName() "</td>");
        out.println("</tr>");
    }
    out.println("</table>");
    out.append("</body></html>");

it gives this error : java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class entity.Subjects ([Ljava.lang.Object; is in module java.base of loader 'bootstrap'; entity.Subjects is in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @7aeb7c5e)

I didn't do @Manytoone Annotation as I read here( How to make this select * from two joined tables query in HQL form?) you can also work without them.

I have tried various things but to no avail. Can someone please tell me why this is happening and how to fix this?

CodePudding user response：

explicit cast is needed, so use the code below instead:

List<Subjects> subjects = 
session.createQuery(
          "select s from Subjects s, Assign a where s.sId = a.sId and 
           a.classId = 2", Subjects.class).list();