Hibernate : attempted to assign id from null one-to-one property: employee

Question

This is my Database structure, One-to-One mapping in MySQL:

This is my java file:

public class Employee {

private EmployeeDetail empdetail;
private String firstname;
private String lastname;

// getters and setters 

}


public class EmployeeDetail {
    private Employee employee ;
    private int employee_id;
    private String street;
    private String city;
    private String state;
    private String country;

// getters and setters 

}

This is my mapping file:

<hibernate-mapping>

     <class name="Employee" table="employee">
        <id name="employee_id"  type="java.lang.Integer"  column="employee_id">
            <generator class="assigned" />
        </id>
        <one-to-one name="empdetail" class="EmployeeDetail"
            cascade="all"></one-to-one>

        <property name="firstname" type="java.lang.String" column="firstname" />
        <property name="lastname" type="java.lang.String" column="lastname" />

    </class>



 <class name="EmployeeDetail" table="employeedetail">
        <id name="employee_id" type="java.lang.Integer"  column="employee_id">
       <generator class="foreign">
                <param name="property">employee</param>
            </generator>
        </id>
        <one-to-one name="employee" class="Employee"
            cascade="save-update"></one-to-one>

        <property name="street"  type="java.lang.String" column="street" />
        <property name="city" type="java.lang.String" column="city" />
        <property name="state" type="java.lang.String" column="state" />
        <property name="country" type="java.lang.String" column="country" />

 </class>

</hibernate-mapping>

This is my client program:

Session session = factory.openSession();
        Transaction tx = session.beginTransaction();

        EmployeeDetail edetail = new EmployeeDetail();
        edetail.setCity("Hyd");
        edetail.setCountry("India");
        edetail.setEmployee_id(222);
        edetail.setState("Andhra Pradesh");

        Employee employee = new Employee();

        employee.setEmployee_id(222);
        employee.setFirstname("Pavan");
        employee.setLastname("Jaooi");
        employee.setEmpdetail(edetail);

        session.merge(employee);
        tx.commit();
        session.close();
        factory.close();

This is the exception I am getting:

INFO: Not binding factory to JNDI, no JNDI name configured
Hibernate: select employee0_.employee_id as employee1_0_1_, employee0_.firstname as firstname0_1_, employee0_.lastname as lastname0_1_, employeede1_.employee_id as employee1_1_0_, employeede1_.street as street1_0_, employeede1_.city as city1_0_, employeede1_.state as state1_0_, employeede1_.country as country1_0_ from employee employee0_ left outer join employeedetail employeede1_ on employee0_.employee_id=employeede1_.employee_id where employee0_.employee_id=?
Hibernate: select employeede0_.employee_id as employee1_1_0_, employeede0_.street as street1_0_, employeede0_.city as city1_0_, employeede0_.state as state1_0_, employeede0_.country as country1_0_ from employeedetail employeede0_ where employeede0_.employee_id=?
Exception in thread "main" org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property: employee
    at org.hibernate.id.ForeignGenerator.generate(ForeignGenerator.java:44)
    at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:99)
    at org.hibernate.event.def.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:186)
    at org.hibernate.event.def.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:240)
    at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:120)
    at org.hibernate.impl.SessionImpl.fireMerge(SessionImpl.java:687)
    at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:669)
    at org.hibernate.engine.CascadingAction$6.cascade(CascadingAction.java:245)
    at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:268)
    at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:216)
    at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
    at org.hibernate.engine.Cascade.cascade(Cascade.java:130)
    at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:456)
    at org.hibernate.event.def.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:194)
    at org.hibernate.event.def.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:240)
    at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:120)
    at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:53)
    at org.hibernate.impl.SessionImpl.fireMerge(SessionImpl.java:677)
    at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:661)
    at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:665)
    at CustomerClient.main(CustomerClient.java:31)

Answer 1

I got the same error here. In my case I was trying to create the relation one-to-one, using the shared Primary Key between the parent and the child class. I resolved the issue by adding in my parent class, inside the "set" method for the definition of the child class, the "this.childClassName.setParentClass(this)".

e.g:

Parent Class

@Entity
@Table(name = "TB_CLIENTS")
public class ClientModel {

    @Id
    @Column(name = "cpf", nullable = false, length = 11)
    private String cpf;
    
    @Column(name = "full_name", nullable = false, length = 80)
    private ClientName fullName;

    @OneToOne(mappedBy = "client", cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn
    private HomeAddress homeAddress; // the instance of the child class inside the parent class

    ... getters and setters

    public void setHomeAddress(HomeAddress homeAddress) {
        this.homeAddress = homeAddress;
        this.homeAddress.setClient(this); // setting the parent class as the value for the child instance
    }

}

Child Class

@Entity
@Table(name = "TB_HOME_ADDRESS")
public class HomeAddress {
    
    @Id
    @Column(name = "client_cpf")
    private String id;
    
    @OneToOne 
    @MapsId
    @JoinColumn(name = "client_cpf")
    private ClientModel client;
    
    ... other attributes + getters and setters
}

Answer 2

You told Hibernate to generate the EmployeeDetail ID from the ID of its employee property, but you never initialized this property.

Add edetail.setEmployee(employee); to your code.