Re: OJB and recursive relationship

Mon, 16 Dec 2002 08:11:47 -0800

Sylvain,

Actually my example wouldn't work for a reference (it needs access to the indirection table "QualifiedARef" and OJB doesn't support this yet AFAIK). A collection in the A class descriptor should work though:

<collection-descriptor
name="qualifiedARefs"
element-class-ref="QualifiedARef"
auto-retrieve="true"
auto-update="false"
indirection-table="QualifiedARef"
>
<fk-pointing-to-this-class column="QUALIFIEDAREF_PK"/>
<fk-pointing-to-element-class column="A_ID_FK"/>
</collection-descriptor>

Phil

Phil Warrick wrote:
Sylvain,

Something like this?

<class-descriptor
      class="A"
      table="A"
   >
      <field-descriptor id="1"
         name="A_id"
         column="A_ID_PK"
         jdbc-type="INTEGER"
         primarykey="true"
         autoincrement="true"
      />
      <field-descriptor id="2"
         name="name"
         column="NAME"
         jdbc-type="VARCHAR"
      />
      <reference-descriptor
         name="qualifiedARef"
         class-ref="QualifiedARef"
      >
         <foreignkey field-id-ref="4"/>
      </reference-descriptor>
</class-descriptor>

<class-descriptor
      class="QualifiedARef"
      table="QualifiedARef"
   >
      <field-descriptor id="1"
         name="qualifiedId"
         column="QUALIFIEDAREF_PK"
         jdbc-type="INTEGER"
         primarykey="true"
         autoincrement="true"
      />
      <field-descriptor id="2"
         name="A_id"
         column="A_ID_FK"
         jdbc-type="INTEGER"
      />
      <field-descriptor id="3"
         name="relationInfo"
         column="RELATION_INFO"
         jdbc-type="VARCHAR"
      />
      <reference-descriptor
         name="classARef"
         class-ref="A"
      >
         <foreignkey field-id-ref="2"/>
      </reference-descriptor>
</class-descriptor>

Phil

[EMAIL PROTECTED] wrote:


Phil,

Ok but how do you do the self-reference?

Sorry I don't understand.

Sylvain


-----Message d'origine-----
De: Phil Warrick [mailto:[EMAIL PROTECTED]]
Date: lundi, 16. d�cembre 2002 16:43
�: OJB Users List
Objet: Re: OJB and recursive relationship


Sylvain,

Only one A fk is required in the QualifiedARef table:

QualifiedARef
-------------
int qualifiedARef_PK
String relationInfo
int A_id_FK

Phil


 >
[EMAIL PROTECTED] wrote:
So, more in practise:

Classes:

Class A { Classe QualifiedARef {
int A_id int qualifiedId
String name A classARef
QualifiedARef qualifiedARef String relationInfo ... int A_id
} ....
}


Relationnal tables:

A QualifiedARef
- -------------
int A_id_PK int qualifiedARef_PK
String name int A_id_class_ref_FK
String relationInfo
int A_id_FK


Am I on the right way?
is there a probem in the QualifiedARef table because there are 2 FK for A??

Thank you
Regards
Sylvain




-----Message d'origine-----
De: Phil Warrick [mailto:[EMAIL PROTECTED]]
Date: lundi, 16. d�cembre 2002 15:59
�: OJB Users List
Objet: Re: OJB and recursive relationship


Hi Sylvain,

Yes, then class A instead has a reference to a class QualifiedARef (or a collection of these). QualifiedARef holds the relation info and a reference to the target A. If bidirectionality is important, it can hold a reference to both of the As in the relation.

Phil

[EMAIL PROTECTED] wrote:


Hi Phil,

Thank you for your answer.
Is it also possible if you qualified this self reference (add information about relation)?

For example if class A have a reference to another instance of class A and this reference has information like reference_name or something like that.

Regards
Sylvain

-----Message d'origine-----
De: Phil Warrick [mailto:[EMAIL PROTECTED]]
Date: lundi, 16. d�cembre 2002 15:14
�: OJB Users List
Objet: Re: OJB and recursive relationship


Hi Sylvain,

OJB handles self references fine. In other words class A can have a reference to another instance of class A or a collection of class As. You may need to make these proxies if the graph is very large and you need to control the hits to the db.

Phil

[EMAIL PROTECTED] wrote:



Hello,

I have a situation with recursive relationship:

I have a class Software that represents the softwares that could be installed on my machine. Some of these softwares must have other softwares installed before to be able to be installed.
So, I have a recurvive relationship here.

How do you implement this relationship with OJB?

Thank you
Sylvain

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