mapping One-to-One fileds

mansour · **Joined:** Sat May 19, 2007 12:02 pm **Posts:** 19

I am new to hibernate and to ORM in general.
How do I map a filed in a class to another field in different class ?

If I have a property Employee.title that Should have a the value of Position.name and not the class position, how do I get around this ?

in other words, there's a table called Employee. title is one of the fileds in that table. And I have another table called Position that contains a field called positionName. How do I get Employee.title = Position.positionName ?

mansour · **Joined:** Sat May 19, 2007 12:02 pm **Posts:** 19

OK all I need is a tip or a link to a tutorial!

himawan · **Joined:** Sat Aug 19, 2006 6:31 pm **Posts:** 139

I guess you want Employee.title to be a foreign key to Position.name?

Here's one way how to do it.
http://www.hibernate.org/hib_docs/v3/re ... -manytoone

amila733 · **Posted:** Thu May 24, 2007 1:22 am

Hi

Employee

EmpId
EmpName
EmpTitle

Position
PositionId
PositionName

This is not exactly what you want. but your table structure might like this. Here EmpTitle foreign key is PositionId. With that link you can find position name. Don't use description type fields to foreignkey constrains.

hibernate mapping files may look like this.

Employee.hbm.xml

Code:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping
>     
    <class
        name="test.Employee"
        table="Employee"
    >

       <id
            name="EmpId"
            column="EmpId"
            type="java.lang.Long"
        >
            <generator class="assigned">
             </generator>
        </id>

             <many-to-one
                 name="tool"
                 class="test.Position"
                 cascade="none"
                 update="true"
                 insert="true"
            lazy="false"
            column="EmpTitle"
        />

   <property
            name="EmpName"
            type="java.lang.String"
            update="true"
            insert="true"
            column="EmpName"
        />
       
    </class>

</hibernate-mapping>

Position.hbm.xml

Code:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping
>     
    <class
        name="test.Position"
        table="Position"
    >

       <id
            name="PositionId"
            column="PositionId"
            type="java.lang.Long"
        >
            <generator class="assigned">
             </generator>
        </id>
             
   <property
            name="PositionName"
            type="java.lang.String"
            update="true"
            insert="true"
            column="PositionName"
        />
       
    </class>

</hibernate-mapping>

Amila

(Don't forget to rate if helps)

mansour · **Joined:** Sat May 19, 2007 12:02 pm **Posts:** 19

What is tool?

Code:

<many-to-one
                 name="[color=red]tool[/color]" 

The corresponding java classes are:

Code:

 class Employee
{
private int EmpId;
private String EmpName ;
private String EmpTitle ;
//getters and setters here ..
}

and

Code:

class Position {
private int PositionId;
private String PositionName;
//getters and setters here ..
}

Now how would hibernate tell that Employee1 is mapped to Position2 ?
Thank you.

amila733 · **Posted:** Thu May 24, 2007 7:43 am

Hi

Employee.hbm.xml

Code:

<?xml version="1.0" encoding="UTF-8"?> 

<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 

<hibernate-mapping 
>      
    <class 
        name="test.Employee" 
        table="Employee" 
    > 

       <id 
            name="EmpId" 
            column="EmpId" 
            type="java.lang.Long" 
        > 
            <generator class="assigned"> 
             </generator> 
        </id> 

             <many-to-one 
                 name="pos" 
                 class="test.Position" 
                 cascade="none" 
                 update="true" 
                 insert="true" 
            lazy="false" 
            column="EmpTitle" 
        /> 

   <property 
            name="EmpName" 
            type="java.lang.String" 
            update="true" 
            insert="true" 
            column="EmpName" 
        /> 
        
    </class> 

</hibernate-mapping>

Code:

class Employee 
{ 
private int EmpId; 
private String EmpName ; 
private Position pos; 
private int positionID;

public String getEmpTitle(){

    return pos.getPositionName();
}


//getters and setters here .. 
}

You didn't rate my answer

Amila
(Don't forget to rate)

mansour · **Joined:** Sat May 19, 2007 12:02 pm **Posts:** 19

Amila:
BUt this doesn't make the field Employee.title = Posistion.name. This is the mapping I was looking for. Is this possible ?

amila733 · **Posted:** Thu May 24, 2007 8:43 am

Hi

No. You must have a link between two tables. it is EmpTitle. it links to Position table. So when you are loading a Employee object in hibenate, it will load automatically Position object which related to that Employee. You can use same position to another employee. That is the benifit of relational db.

Amila

(Don't forget to rate)

mansour · **Joined:** Sat May 19, 2007 12:02 pm **Posts:** 19

That was alot of help. I will rate your answer again.