休眠：OneToMany关联不起作用未知实体错误

Question

I am getting the following error when I am trying to create a one-to-many association

Exception in thread "main" org.hibernate.MappingException: Unknown entity: org.hibernate.collection.internal.PersistentBag

Here is where the code to create the association is run

public void assignDoctorSpecialty(Doctor doctor, Specialty specialty) {
    Session session = sessionFactory.openSession();
    session.beginTransaction();

    doctor.setSpecialty(specialty);

    List<Doctor> doctors = specialty.getDoctors();
    doctors.add(doctor);

    session.save(doctors);
    session.getTransaction().commit();
    session.close();

}

Here is my Doctor class

package edu.cs157b.hibernate;

import java.util.ArrayList;

import javax.persistence.*;

@Entity
@Table(name="DOCTOR_INFO")
@NamedQueries (
    {
        @NamedQuery(name = "Doctor.getAll", query = "from Doctor"),
        @NamedQuery(name = "Doctor.findByName", query = "from Doctor where name = :name")
    }
)
public class Doctor implements Person {

    private int id;
    private String name;
    private Specialty specialty; 

    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Column(unique=true)
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @ManyToOne (fetch = FetchType.EAGER, cascade= CascadeType.PERSIST) 
    @JoinColumn(name="specialty_id") 
    public Specialty getSpecialty() {
        return specialty;
    }

    public void setSpecialty(Specialty specialty) {
        this.specialty = specialty;
    }
}

Here is my Specialty class

package edu.cs157b.hibernate;

import java.util.ArrayList;

import javax.persistence.*;

import java.util.List;

@Entity
@Table(name="SPECIALTY_INFO")
@NamedQueries (
    {
        @NamedQuery(name = "Specialty.getAll", query = "from Specialty"),
        @NamedQuery(name = "Specialty.findByName", query = "from Specialty where name = :name")
    }
)
public class Specialty {
    private List<Doctor> doctors = new ArrayList<Doctor>();

    private int id;
    private String name;

    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

    @Column(unique=true)
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @OneToMany(mappedBy="specialty", targetEntity = Doctor.class, 
             fetch=FetchType.LAZY, cascade= CascadeType.PERSIST) 
    public List<Doctor> getDoctors() {
        return doctors;
    }
    public void setDoctors(List<Doctor> doctors) {
        this.doctors = doctors;
    }    

}

EDIT

If I save the Doctor object directly, instead of trying to indirectly save it through Cascade saving the Specialty doctor list, it throws no error. However, when I go into my database, specialty_id of the Doctor table is not set.

Answer 1

As far as I know it is not possible to persist a collection of objects using the save(..) method. Try the following code:

public void assignDoctorSpecialty(Doctor doctor, Specialty specialty) {

    [...]

    for (Doctor d : doctors) {
         session.save(d);
    }

    session.getTransaction().commit();
    session.close();
}

Answer 2

I figured out the answer. The reason this happens is because I try to save an object that was already saved in the database. All I had to do was replace session.save(doctor) with session.saveOrUpdate(doctor) .