如何在休眠中实现一对一的外键关系映射

Question

I am trying to implement a one to one hibernate relationship mapping and I am new to hibernate technology. My two entity classes are Employee and Client . Client should have a employee ID column as foreign key in database table; ie this client is handled by this employee. Now there are two jsp pages through which I will submit the details of employee and client. First I will add/submit employee jsp. Then on client jsp page there would be a select box consisting employeeIDs as its value. I have done my jsp part. But I am doubtful of my one to one mapping relationship of client with employee. So I am providing my files of code. Below is my code :

employee class:

public class RWEmp {
    private int id; 
    private String strName;
    private String strContactNum;
    private String strDateOfJoining;
    private String strDesignation;
    public RWEmp(){
    }
    // getter/setters
}

client class:

public class RWClient {
    private int id;
    private String strName;
    private RWEmp poc_emp;  // point of contact employee as employee object
    public RWClient(){
    }
    // getter/setters
}

employee.hbm.xml is straight forward. ie no relationship. But client is having a has a relation with employee object.

client.hbm.xml:

<hibernate-mapping>
    <class name="com.rightwave.entities.RWClient" table="client_master">
        <id name="id" type="int">
            <generator class="increment" />
        </id>
        <property name="strName" type="string" column="cl_name" />
        <many-to-one name="poc_emp" class="com.rightwave.entities.RWEmp" column="poc_emp" unique="true"></many-to-one>
    </class>
</hibernate-mapping>   

persisting class:

public class PersistEntities {

    public void clientPersist() {
        Session session=Factory.getSession();
        Transaction tr=session.beginTransaction();

        RWEmp rwEmp =new RWEmp();
        rwEmp.setId(2); // this will come from jsp page <select> value. I am doubtful of this, explained below in question.

        RWClient rwClient1=new RWClient("wso2",rwEmp);

        session.save(rwClient1);
        session.flush();
        tr.commit();
        session.close();
    }
}

Here I am not sure if this blueprint is right or wrong. Can I set the employee ID, which will come from my client jsp page (from in <select> box). I am confused because here I am only setting employee ID, which has to be already existing to be a valid foreign key of client. But there are no checks of validating whether this employee ID is already existing or not. The Employee object will definitely be saved (from employee.jsp ) before client object. Am I doing it right way?

Answer 1

When establishing one-to-one relationship with two entities both are assigned the same primary key. A special foreign identifier generator should be declared on Client table to get the primary key value from Employee table. Add constrained="true" to ensure the Employee exists.

<hibernate-mapping>
    <class name="com.rightwave.entities.RWClient" table="client_master">        
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="foreign">
                <param name="property">poc_emp</param>
            </generator>
        </id>
        <one-to-one name="poc_emp" class="com.rightwave.entities.RWEmp"
            constrained="true"></one-to-one>
        <property name="strName" type="string" column="cl_name" />        
    </class>
</hibernate-mapping>