I am new to Hibernate and I am trying to get some data from the database. I don't want to get the full data but a projection of an entity.
The thing is that in the for-loop when I get the id and the name of my projection, it gets the default values id=0 and name=null instead of id=7 and name="Name 8" which are the records of the original entity in the database. Do you know what causes this problem? The for-loop is in the last code.
Here is the Student Entity
@Entity(name = "Students")
public class Student {
@Id
@GeneratedValue
@Column(name = "StudentId")
private int id;
@Column(name = "Name", nullable = false, length = 50)
private String name;
@Column(name = "Grade")
private Double grade = null;
@ManyToOne(cascade = CascadeType.PERSIST)
@JoinColumn(name = "FacultyId", nullable = false)
private Faculty faculty;
@ManyToMany(cascade = CascadeType.PERSIST)
@JoinTable(
joinColumns = @JoinColumn(name = "StudentId"),
inverseJoinColumns = @JoinColumn(name = "CourseId"))
private Collection<Course> courses;
public Student() {
this.courses = new HashSet<Course>();
}
// Setters and Getters for all fields
}
Here is the StudentModel
public class StudentModel {
private int id;
private String name;
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
}
And the code I am executing
Session session = sessionFactory.openSession();
session.beginTransaction();
{
Criteria criteria = session.createCriteria(Student.class);
criteria.add(Restrictions.eq("name", "Name 8"))
.setProjection(
Projections.projectionList()
.add(Projections.property("id"))
.add(Projections.property("name")))
.setResultTransformer(
Transformers.aliasToBean(StudentModel.class));
@SuppressWarnings("unchecked")
List<StudentModel> students = criteria.list();
for (StudentModel student : students) {
System.out.println(student.getId());
System.out.println(student.getName());
}
session.getTransaction().commit();
session.close();
}
You probably simply forgot to assign aliases to your projections:
Projections.projectionList()
.add(Projections.property("id"), "id")
.add(Projections.property("name"), "name")