Re: Problem with n:m association

Sun, 05 Dec 2004 04:43:59 -0800 

Ok i have solved the problem.

There was no pk defined for my class called "meinung", because i develop step by step and meinung was not yet complet (i found this with some more debugging infos in ojb). So in detail there was not problem with my n:m association.

So thanks for your help....
But here you see that a better error message should occur - not only devide by zero.

Thomas

Armin Waibel schrieb:


Thomas Papke wrote:

Hi ...

yes that could be the problem. For the tables "Produktgruppe" and "Produkt", i have defined the primary keys in the deskriptor. The table for decompose the n:m mapping "produkt_produktgruppe" - i have nothing defined in the descriptor.


As you are using a non-decomposed m:n relation the indirection table "produkt_produktgruppe" couldn't be a persistent class, so you shouldn't define a class-descriptor for the indirection table or set the FK fields from product and group as PK fields.

regards,
Armin


Because as described in the docs of ojb http://db.apache.org/ojb/docu/guides/basic-technique.html#Support+for+Non-Decomposed+m%3An+Mappings it should work.

Did i something wrong?
On the bottom of this email again the interessting parts of my descriptor where you could see that i have defined the pk's for produktgruppe and produkt in a correct way.

Is the possibly a bug of ojb or is something necessary what is not mentioned in the example for n:m ojb mapping?

Thanks, Thomas

Armin Waibel schrieb:

Hi Thomas,

Thomas Papke wrote:

The excectly exception (after broker.getCollectionByQuery ...) i got from ojb broker is:

org.apache.ojb.broker.PersistenceBrokerException: java.lang.ArithmeticException: / by zero


In the source the causing line is

at BasePrefetcher.<init>(BasePrefetcher.java:76)
...
pkLimit = getPrefetchInLimit() / getItemClassDescriptor().getPkFields().length;
...

Seems that OJB get a persistent class without defined PK fields. Could this be the case?

regards,
Armin


Thomas Papke schrieb:

Thanks for your answer.

I need the inId because its like ebay: in each productgroup there is a collection of "untergruppen/undergroups". And this works: i could add objects of produktgruppe and save them (so inId will store the reference to the main productgroup).

The problem is not between productgroup and productgroup (1:n) - it is between Productgroup and Product (n:m)

And why did i got a arithmetic exception (/ by zero) from the ojb core??

I found also something strange:
The OJB Framwork and my Application runs in a Tomcat environment.
If i start tomcat and then my app - i got the error! If i start my app a seconde time everthing works fine ...

Thanks for help, Thomas


Thomas Franke schrieb:

Thomas Papke wrote:

Why you need the inId?


Here is my descriptor of the two classes:

<class-descriptor
   class="de.ba.studi.chtp.model.Produktgruppe"
   table="Produktgruppe"
 >
   <field-descriptor
       name="id"
       column="id"
       jdbc-type="INTEGER"
       primarykey="true"
       autoincrement="true"
   >
   </field-descriptor>
   <field-descriptor
       name="inId"
       column="inId"
       jdbc-type="INTEGER"
   >
   </field-descriptor>
   <field-descriptor
       name="name"
       column="name"
       jdbc-type="VARCHAR"
   >








I thing this can't work and I thing also it is a wrong design:

   </field-descriptor>
   <collection-descriptor
      name="produktgruppen"
      element-class-ref="de.ba.studi.chtp.model.Produktgruppe"
      orderby="inId"
      sort="DESC"
      auto-retrieve="true"
      auto-update="true"
      auto-delete="true"
   >
      <inverse-foreignkey field-ref="inId"/>
   </collection-descriptor>









   <collection-descriptor
      name="produkt"
      element-class-ref="de.ba.studi.chtp.model.Produkt"
      auto-retrieve="true"
      auto-update="true"
      indirection-table="produkt_produktgruppe"
 >
      <fk-pointing-to-this-class column="ProdGruppe_id"/>
      <fk-pointing-to-element-class column="Prod_Id"/>
 </collection-descriptor>
</class-descriptor>


Take into your Produkt class a collection descriptor with Produktgruppe classes.
For that case I would write a spezial mapping for Produktgruppe without a collection with Produkt class.

<class-descriptor
   class="de.ba.studi.chtp.model.Produkt"
   table="Produkt"
 >
   <field-descriptor
       name="id"
       column="id"
       jdbc-type="INTEGER"
       primarykey="true"
       autoincrement="true"
   >
   </field-descriptor>
   <field-descriptor
       name="name"
       column="name"
       jdbc-type="VARCHAR"
   >
   </field-descriptor>


 <collection-descriptor
      name="meinung"
      element-class-ref="de.ba.studi.chtp.model.Meinung"
      auto-retrieve="true"
      auto-update="true"
 >
      <inverse-foreignkey field-ref="prod_id"/>
 </collection-descriptor>
  </class-descriptor>







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