Hi,
http://db.apache.org/ojb/tutorial3.html#using%20proxy%20classes
discusses the use of proxies in detail.
Essentially, if you want to use proxies for a SingleReference they
ultimately will
have to be interfaces so that OJB can generate a DynamicProxy for them.
Our Object model couldn't support that (not in a maintanable way), so what
we've done is to write a RelationshipHelper class that lazily loads a
relationship on demand.
We then implement the getter on the persistence class a bit like this :
public Country getCountry(){
RelationshipHelper.lazyLoad(this,"country");
return country;
}
I realise and acknowledge this isn't ideal, and probably won't help alot of
people, but it solves the problem for us.
Cheers,
Charles
>-----Original Message-----
>From: David Warnock [mailto:[EMAIL PROTECTED]]
>Sent: 13 February 2003 10:21
>To: [EMAIL PROTECTED]
>Subject: How to do Lazy Foreign Keys?
>
>
>Hi,
>
>I have solved my earlier problem with simple foreign key relationships
>and they now work.
>
>But how do I avoid loading the parent object before it is required?
>
>I know I can use a single proxy for a whole collection BUT what is the
>equivilent for single foreign key relationships like this
>
>
> <class-descriptor
> class="org.visres.contact.data.Country"
> table="Countries"
> >
> <field-descriptor
> name="countryId"
> column="CountryId"
> jdbc-type="INTEGER"
> primarykey="true"
> autoincrement="true"
> sequence-name="GEN_CountryId"
> />
> <field-descriptor
> name="name"
> column="Name"
> jdbc-type="VARCHAR"
> />
> </class-descriptor>
>
> <class-descriptor
> class="org.visres.contact.data.State"
> table="States"
> proxy="dynamic"
> >
> <field-descriptor
> name="stateId"
> column="StateId"
> jdbc-type="INTEGER"
> primarykey="true"
> autoincrement="true"
> sequence-name="GEN_StateId"
> />
> <field-descriptor
> name="name"
> column="Name"
> jdbc-type="VARCHAR"
> />
> <field-descriptor
> name="countryId"
> column="CountryId"
> jdbc-type="INTEGER"
> />
> <reference-descriptor
> name="country"
> class-ref="org.visres.contact.data.Country"
> >
> <foreignkey field-ref="countryId"/>
> </reference-descriptor>
> </class-descriptor>
>
>
>So when I load a State I don't want to load it's country unless I call
>state.getCountry().
>
>Thanks
>
>Dave
>--
>David Warnock, Sundayta Ltd. http://www.sundayta.com
>iDocSys for Document Management. VisibleResults for Fundraising.
>Development and Hosting of Web Applications and Sites.
>
>
>
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