AnnotationException Referenced property not a (One|Many)ToOne

Question

I tried to make one-to-one relationship. But I get error:

AnnotationException Referenced property not a (One|Many)ToOne
on
com.student.information.service.Department.departmentId in mappedBy of com.student.information.service.DepartmentHead.department

Both the entities are almost identical. Department can exists with out department head.

Department.Java

@Entity
@Table(name="department", catalog="student")
public class Department {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer departmentId;

    @Column(name="dept_name")
    private String departmentName;

    @OneToMany(mappedBy="department",cascade = CascadeType.ALL)
    private List<Student> student; 

    @OneToOne(targetEntity=Department.class)
    private DepartmentHead departmenthead;
}       

DepartmentHead.java

@Entity
@Table(name="departmenthead", catalog = "student")
public class DepartmentHead {

    //This is mapped with the department id

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    @Column(name="headname")
    private String headName;

    @OneToOne(mappedBy = "departmentId",fetch = FetchType.LAZY,cascade=CascadeType.ALL)
    @JoinColumn(name="dept_id")
    private Department department;  
}

Caused by: org.hibernate.AnnotationException: Referenced property not a (One|Many)ToOne:

can someone please point me in the right direction about what mistake am I making. I am struggling from past 2 days and not able to figure out the solution for the issue. Thanks in advance for help.

Answer 1

You have incorrectly set up your mapping. Hibernate is complaining that no field called departmentId is available to set up a one to one or many relationship, and it is correct.

You want to map your values like this.

Department.Java

@Entity
@Table(name="department", catalog="student")
public class Department {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer departmentId;

    @OneToOne
    @JoinColumn(name = "id")
    private DepartmentHead departmenthead;
}       

DepartmentHead.java

@Entity
@Table(name="departmenthead", catalog = "student")
public class DepartmentHead {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    @OneToOne(mappedBy = "departmenthead")
    private Department department;  
}

You point the Department field in DepartmentHead at the DepartmentHead field inside the Department. Hibernate sorts out what ID's to use, you don't have to specify that in the actual link.