What would be my JPA Entities ??

Question

Hello Everyone.
I have a confusion.
In my database i have 3 tables.
1) University (id, Name)
2) Specialization (id, Name)
3) Degree (id, Name)
and one relationship table.
4) degree_prog_replationshiip (id, university_id, specialization_id, degree_id)
i am not able to design my entity classes.
Please tell me how would be my entity classes?
Thanks.

Answer 1

>
>
> In the degree entity for example it has a one to many relationship expressed as a List of degree_prog_replationship entities. Then in the degree_prog_replationship entity you have a many to one relationship to the degree entity. Then the same for each of the other 2 entity types.
>
Here entity classes.
University.java package entities;
import java.io.Serializable;
import java.util.List;
import javax.persistence.*;
@Entity
@Table(name="university")
public class University implements Serializable {
@Id
@GeneratedValue(generator="university_id_seq",strategy=GenerationType.SEQUENCE)
@Column(name="id")
private int universityId = 0;
@Column(name = "name")
private String universityName = "";
@OneToMany(mappedBy="university",cascade=CascadeType.PERSIST,CascadeType.REMOVE})
private List<DegreeProgam> degreeProg;
public void University(){ }
public void setUniversityId(int universityId) { this.universityId = universityId; }
public int getUniversityId() { return this.universityId; }
public void setUniversityName(String universityName) {
this.universityName = universityName;
public String getUniversityName() { return this.universityName; }
public List<DegreeProgram> getDegreeProg() { return degreeProg; }
public void setDegreeProg(List degreeProg) {
this.degreeProg = degreeProg;
} }Specialization.java
package entities;
import java.io.Serializable;
import java.util.List;
import javax.persistence.*;
@Entity
@Table(name="specialization")
public class Specialization implements Serializable {
@Id
@GeneratedValue(generator="specialization_id_seq",strategy=GenerationType.SEQUENCE)
@Column(name="id")
private int specializationId = 0;
@Column(name="name")
private String specializationName = "";
public void Specialization() { }
public void setSpecializationId(int specializationId) {
this.specializationId = specializationId;
public int getSpecializationId() { return this.specializationId;}
public void setSpecializationName(String specializationName) {
this.specializationName = specializationName;
public String getSpecializationName() { return this.specializationName;}
}Degree.java
package entities;
import java.io.Serializable;
import java.util.List;
import javax.persistence.*;
@Entity
@Table(name="degree")
public class Degree implements Serializable {
@Id
@GeneratedValue(generator="degree_id_seq",strategy=GenerationType.SEQUENCE)
@Column(name="id")
private int degreeId = 0;
@Column(name="name")
private String degreeName = "";
public void Degree() { }
public void setDegreeId(int degreeId) {
this.degreeId = degreeId;
public int getDegreeId() { return this.degreeId; }
public void setDegreeName(String degreeName) {
this.degreeName = degreeName;
public String getDegreeName() { return this.degreeName; }
}and last one .DegreeProgram.java
package entities;
import java.io.Serializable;
import javax.persistence.*;
@Entity
@Table(name="degree_program_relationship")
public class DegreeProgram implements Serializable{
    @Id
    @GeneratedValue
    @Column(name="id")
    private int degreeProgramId = 0;
    @ManyToOne
    @JoinColumn(name="university_id")
    private University uni;
    @ManyToOne
    @JoinColumn(name="specialization_id")
    private Specialization spec;
    @ManyToOne
    @JoinColumn(name="degree_id")
    private Degree deg;
    public void DegreeProgram() { }
    public int getDegreeProgramId() { return degreeProgramId; }
    public void setDegreeProgramId(int degreeProgramId) {
        this.degreeProgramId = degreeProgramId;
    public Degree getDeg() { return deg; }
    public void setDeg(Degree deg) { this.deg = deg; }
    public Specialization getSpec() { return spec; }
    public void setSpec(Specialization spec) { this.spec = spec; }
    public University getUni() { return uni; }
    public void setUni(University uni) { this.uni = uni; }
}after that when i tried to run my code i got the error
oracle.toplink.essentials.exceptions.ValidationException
Exception Description: The attribute [degreeProg] in entity class [class entities.University] has a mappedBy value of [uniersity] which does not exist in its owning entity class [class entities.DegreeProgram]. If the owning entity class is a @MappedSuperclass, this is invalid, and your attribute should reference the correct subclass.Please help me. Thanks.