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Posted to ojb-user@db.apache.org by Thomas Dudziak <to...@first.fhg.de> on 2004/09/22 11:01:26 UTC
Re: Collection + foreignkey missing
BOUESSAY Christian wrote:
>Hello,
>
>There is an association (1:n) between 2 classes:
>
>
>/**
> * @ojb.class
> * @ojb.field name="idOM" jdbc-type="INTEGER"
> */
>public class Label {
> /**
> * @ojb.field primarykey="true"
> */
> private int id;
>
> // ...
>}
>
>
>/**
> * @ojb.class
> */
>class OM {
>
> /**
> * @ojb.field primarykey="true"
> */
> private int id;
>
> /**
> * @ojb.collection element-class-ref="Label"
> * foreignkey="idOM"
> */
> private Collection labels;
>
> // ...
>}
>
>
>In the repository_user.xml :
><collection-descriptor
> name="labels"
> element-class-ref="Label"
>
>
> <inverse-foreignkey field-ref="idOM"/>
></collection-descriptor>
>
>
>In the project-schema.xml, there is no <foreign-key> declaration for the table OM ...
>
>What did I miss?
>
>
For collections, the generation of foreignkeys in the database is
currently not supported due to the complexities involved when having
indirection tables, inheritance etc.
Tom
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Re: Collection + foreignkey missing
Posted by Thomas Dudziak <to...@first.fhg.de>.
Christian Pesch wrote:
> Are there plans to implement this?
Erm, yes, but I don't know when ;-( I'm a bit swamped at the moment ...
Tom
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Re: Collection + foreignkey missing
Posted by Christian Pesch <ch...@coremedia.com>.
Thomas Dudziak wrote:
> [..]
> Implementing this analysis therefore requires determining what cases
> can possibly arise and then quite some implementation work (esp. unit
> tests).
Are there plans to implement this?
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Re: Collection + foreignkey missing
Posted by Thomas Dudziak <to...@first.fhg.de>.
Christian Pesch wrote:
> Could you explain, where the complexity comes from?
> The requirement to define foreign keys on the database schema seems
> reasonable to me. At least, I've copied the schema definition in my
> application
> and added foreign key constraints to it.
>
> Maybe one could take some assumptions and eliminate the need for a
> manual step
> in a simple setup without redirection tables and inheritance and ...?
The problem comes from the necessity to analyze whether a foreignkey can
be placed safely or not. For instance, you cannot define a foreignkey
constraint upon an indirection table if this table is used by a normal
class descriptor as well. It can get even more complex if you have
inheritance for one end of the collection, say via super-references
(which is only implicit in the repository).
Implementing this analysis therefore requires determining what cases can
possibly arise and then quite some implementation work (esp. unit tests).
Tom
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Re: Collection + foreignkey missing
Posted by Christian Pesch <ch...@coremedia.com>.
Thomas Dudziak wrote:
> BOUESSAY Christian wrote:
>
>> There is an association (1:n) between 2 classes:
>> [..]
>> In the project-schema.xml, there is no <foreign-key> declaration for
>> the table OM ...
>>
>> What did I miss?
>
> For collections, the generation of foreignkeys in the database is
> currently not supported due to the complexities involved when having
> indirection tables, inheritance etc.
Could you explain, where the complexity comes from?
The requirement to define foreign keys on the database schema seems
reasonable to me. At least, I've copied the schema definition in my
application
and added foreign key constraints to it.
Maybe one could take some assumptions and eliminate the need for a
manual step
in a simple setup without redirection tables and inheritance and ...?
Christian
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