Hi, I get stuck with derived properities. I find there are few materials available and I have not found any examples.

I am using Hibernate 2.1.7 and Microsoft SQL Server.

I used net.sf.hibernate.tool.hbm2java.Hbm2JavaTaskto generate code
and net.sf.hibernate.tool.hbm2ddl.SchemaExportTask to generate
schema. I wrote the testing code.

I never see the derived properity has a correct value. In the
example below, I hope to see 9 assigned to the derived property *total*,
but it is always 0.0 before and after save or commit. Why?
What is the correct way to do a derived property?
What went wrong?

Thanks a lot!
Pete


The following are 3 complete files:
hibernate mapping file, generated java class file, and the testing code.

----------------------------------------------------------------
Here is the complete mapping file:
----------------------------------------------------------------

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>

<class name="DerivedProperty" table="DERIVED_TABLE">
<meta attribute="implement-equals">true</meta>

<id name="id" type="long" column="ID">
<meta attribute="scope-set">private</meta>
<generator class="native"/>
</id>

<property name="quantity" type="integer" not-null="true">
<meta attribute="use-in-tostring">true</meta>
<column name="QUANTITY"/>
</property>

<property name="total"
formula="QUANTITY * 3" type="double" not-null="true">
<meta attribute="use-in-tostring">true</meta>
</property>

</class>

</hibernate-mapping>


----------------------------------------------------------------
Here is the generated DerivedProperty.java:
----------------------------------------------------------------


import java.io.Serializable;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.ToStringBuilder;


/** @author Hibernate CodeGenerator */
public class DerivedProperty implements Serializable {

/** identifier field */
private Long id;

/** persistent field */
private int quantity;

/** persistent field */
private double total;

/** full constructor */
public DerivedProperty(int quantity, double total) {
this.quantity = quantity;
this.total = total;
}

/** default constructor */
public DerivedProperty() {
}

public Long getId() {
return this.id;
}

private void setId(Long id) {
this.id = id;
}

public int getQuantity() {
return this.quantity;
}

public void setQuantity(int quantity) {
this.quantity = quantity;
}

public double getTotal() {
return this.total;
}

public void setTotal(double total) {
this.total = total;
}

public String toString() {
return new ToStringBuilder(this)
.append("id", getId())
.append("quantity", getQuantity())
.append("total", getTotal())
.toString();
}

public boolean equals(Object other) {
if ( (this == other ) ) return true;
if ( !(other instanceof DerivedProperty) ) return false;
DerivedProperty castOther = (DerivedProperty) other;
return new EqualsBuilder()
.append(this.getId(), castOther.getId())
.isEquals();
}

public int hashCode() {
return new HashCodeBuilder()
.append(getId())
.toHashCode();
}

}


-----------------------------------------------------
Here is the testing code:
----------------------------------------------------------------

import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
import net.sf.hibernate.cfg.Configuration;

/**
*
*/
public class TestPDerivedProperty
{
public static void main(String args[]) throws Exception {

Configuration config = new Configuration();


config.addClass(DerivedProperty.class);

SessionFactory sessionFactory = config.buildSessionFactory();

Session session = sessionFactory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();

DerivedProperty obj = new DerivedProperty();
obj.setQuantity(3);

System.out.println("before save\n"+ obj);

session.save(obj);

System.out.println("after save\n"+ obj);

tx.commit();

System.out.println("after commit \n"+ obj);

} catch (Exception e) {
if (tx != null) {
tx.rollback();
}
throw e;
} finally {
session.close();
}
sessionFactory.close();
}
}

Do I have to create a trigger on the MS SQL table? If yes, then
what is the point specifying the formula in the mapping file?
Can Hibernate ask the MS SQL server to create a trigger automatically
based on the mapping file?

Hibernate is new to me. Can somebody help me out here?

Thanks!

Pete

Is my question too simple and stupid or too hard to answer?

What is the correct way to do derived properties on the database
side and java code side?

Somebody helps, please...

Thanks!

Somebody helps, please...

Thanks!

can somebody shed some light?

thanks.

Actually, hibernate did not read the DB while saving. Consider using refresh()