How can Hibernate persist a non-primitive class ????

mooki · **Joined:** Thu Aug 12, 2004 9:32 am **Posts:** 17

Hi, I have worked with JDO and I am new to Hibernate.
I need your help understanding the way of making class persistent with Hibernate.

Let say I have a class :

Code:

Employee
    private int           empNumber;
    private String        empName;
    private EmpAddr    empAddress; // <---  

As I understand, I have 3 (??) ways of persisting this class :
1) save empAddress in a different table (in db) with relation column to Employee
2) save empAddress as is as an object inside Employee (let say, to a blob in db)
3) save calculated column such as empAddress.toString() to a varchar in db (inside Employee table)

Am I correct with my assumptions ???

Can someone provide me with the syntax for mapping these 3 ways ? ( P L E A S E ......)?

Hibernate version:2.1.6
Name and version of the database you are using:Oracle 8i,9i[/i]

christian · **Posted:** Tue Aug 17, 2004 9:34 am

3) is the correct way to do this, we call this a <component> mapping.

mooki · **Joined:** Thu Aug 12, 2004 9:32 am **Posts:** 17

Thanx Christian,
In that case you can say that 3 is the correct way, but in other cases I might need to save the whole object AS-IS (for complex classes or classes which are not mine)

that is why I do wish to know the syntax of All 3 ways of doing it. that would help me much !!!!

as for using <component>, from what I saw on the hibernate_reference, I use it in order to describe how the internal class (empAddress) looks like and not to use any method like toString of empAddress.....

or I am wrong here also ..?????

christian · **Posted:** Tue Aug 17, 2004 9:52 am

Uhm, I see no way explaining this better, it's already pretty trivial. I don't know why "not own classes" should be different or what "complex" means.

mooki · **Joined:** Thu Aug 12, 2004 9:32 am **Posts:** 17

sorry if my question is too basic.....
anyway,
when I mean complex, I mean that I have a Class

Code:

Class xxx
    private HashMap   memberA;
    private Document memberB; //org.w3c.dom.document
    private int            memberC;

now....
I want to save this class in Oracle in table XXX
and :
a) I dont know how Document should be so i will use blob in db
b) I want to save the HashMap as is so when i read the xxx class from
db I will be able the read the memberA directly to new HashMap....

Is it more clear now ????

[/code]

christian · **Posted:** Tue Aug 17, 2004 10:07 am

Code:

<property name="memberC" type="int"/>
<property name="memberB" type="serializable"/>
<map name="memberA" table="MEMBER_A">
   <key column="XXX_ID"/>
   <index column="MAP_IDX" type="type_of_your_map_key"/>
   <element column="MAP_VALUE" type="type_of_your_map_value"/>
</map>

You know, this is basic stuff covered in the documentation.

mooki · **Joined:** Thu Aug 12, 2004 9:32 am **Posts:** 17

Sorry, I know it is basic stuff and I hoped someone could share some example for these situations. I have the hibernate_reference.pdf and it is lake of examples......

as for using a map, I already tried that and im struggling with this basic stuff !

when I used access="field" I got :
could not set a field value by reflection setter of test.hibernate.Nir.HM
when I used access="property" (default)
and just put setters as :

Code:

public HashMap getHM() {
     return HM;
}
public void setHM(HashMap hm) {
    HM=hm;
    //HM.clear();
    //HM.putAll(hm);   another option i tried
} 

I got:
18:22:15,271 ERROR BasicPropertyAccessor:60 - IllegalArgumentException in class: test.hibernate.Nir, setter method of property: HM
18:22:15,271 ERROR BasicPropertyAccessor:64 - expected type: java.util.HashMap, actual value: net.sf.hibernate.collection.Map
net.sf.hibernate.PropertyAccessException: IllegalArgumentException occurred while calling setter of test.hibernate.Nir.HM
at net.sf.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:68)
at net.sf.hibernate.persister.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:222)

[b]when I used Map instead of HashMap I did not get that problem.[b]

anyone ????

tq · **Posted:** Tue Aug 17, 2004 11:46 am

mooki wrote:

Sorry, I know it is basic stuff and I hoped someone could share some example for these situations. I have the hibernate_reference.pdf and it is lake of examples......

hibernate_reference.pdf is not for examples, have a look at http://www.hibernate.org/152.html instead.

tq · **Posted:** Tue Aug 17, 2004 11:52 am

mooki wrote:

when I used Map instead of HashMap I did not get that problem.

anyone ????

oh yes to answer that question here's hibernates source for Map, which is what was expected.

Code:

public class Map extends PersistentCollection implements java.util.Map, DMap {

that's why java.util.Map was fine and not HashMap.

have ant generate your POJO's and you won't have that problem.
There's a very good tutorial on the link I posted that will take you through everything.

mooki · **Joined:** Thu Aug 12, 2004 9:32 am **Posts:** 17

Thanx tj,
I dont know YET what is POJO's but I hope the i will find it in the links you sent.

Thanx.

anthony · **Posted:** Tue Aug 17, 2004 12:30 pm

pojo (plain old java object)= (business) javabean that is to say you have persistent properties + business rules but without dependencies to another external package

dplass · **Posted:** Tue Aug 17, 2004 4:51 pm

christian wrote:

3) is the correct way to do this, we call this a <component> mapping.

His suggestion of using toString() is NOT the same as a <component> mapping. Using toString during a save would require parsing during the load, which could easily break (think: what separator would be used? You'd have to escape that separator in the generated string).

Using a "real" <component> mapping would work, obviously. I myself would prefer a one-to-many mapping to be more flexible in the future whe you have to support home, work, vacation addresses.

swinfough · **Joined:** Fri Sep 10, 2004 10:21 am **Posts:** 7

I'm having a difficult time mapping a HashMap property. My class "Account" has a hash map of "Payments", which is another class.

My class looks like this...

Code:

public class Account () {
   ...
   private Map payments = new HashMap();

   ...
   public Map getPayments() {
      return this.payments;
   }

   public void setPayments(Map payments) {
      this.payments = payments;
   }
}

May mapping files look like this...

Code:

<class name="Account" table="accounts">
   ...
   <map name="payments" table="payments" cascade="all" access="property" >
        <key column="account_id"/>
       <index column="reference_number" type="string"/>
        <one-to-many class="Payment"/>
    </map>
</class>

<class name="Payment"  table="payments">
   ...
    <property name="referenceNumber" column="reference_number" type="string" length="32" not-null="true" access="field"/>
    <property name="paymentAmount" column="payment_amount" type="big_decimal" access="field" />
</class>

In my Account class, when I add a payment, I use the payment reference number as the key for the HashMap, and the payment object itself as the value for the HashMap.

Code:

// Add the payment to the account's list of unapplied credit payments
this.payments.put(payment.getReferenceNumber(), payment);

And in the code that I call to persist the account I do the following...

Code:

  // get the hibernate session
  Session session = HibernateUtil.getSession();

  // Save the parts of the account that are separate objects in the DB
  session.save(account.getPayments());

  // Save the account
  session.save(account);
  session.flush();

The call to session.save() with the payments throws the exception: No persister for: java.util.HashMap.

So, I have two questions, 1) given what I've included here, am I doing something seriously wrong to cause the exception? 2) Does Hibernate support persisting maps with a class as the map 'value'?

Any insight or direction is greatly appreciated.

swinfough · **Joined:** Fri Sep 10, 2004 10:21 am **Posts:** 7

I think I have solved my own problem. After stairing at the screen for a while longer, after my first post, it finally hit me that I must loop through my HashMap and save the objects it contains! Now I understand the error message "no persistor for: java.util.HashMap". I don't want to save the container, only the objects contained within it.

<< in my best Homer Simpson voice >> Dhooo!

As my colleague commented, as I shared the answer with him,

Quote:

"in the words of Red Foreman from 'That '70's Show'.... 'You dumb a$$'"