Hi,
Did you see my response to your other post? Please reply to the list.
Cheers,
Rob :)
-----Original Message-----
From: Patrick Scheuerer [mailto:[EMAIL PROTECTED]
Sent: Tuesday, 6 January 2004 10:17 a.m.
To: OJB Users List
Subject: How to combine two non-decomposed m:n mappings in one
collection?
Hi,
I have the following problem:
I have a table keywords which has two non-decomposed m:n mappings to the
tables
document and file. The latter two both implement the interface
SupportItem. In
my Keyword class i would like to have a collection of all SupportItems
for this
keyword.
Is it possible to declare two indirection-tables in a
collection-descriptor? If not, how could this be accomplished? Can OJB
handle such a case?
Thanks a lot!
Patrick
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Hi Patrick.
Is the field doc_id in download_pal_model actually meant to be model_id?
Otherwise I am a touch confused :)
Also, I assume you've checked out the advanced O/R mapping stuff at
http://db.apache.org/ojb/tutorial3.html - if not, do it now!
Idea #1:
For download -> model
<class-descriptor class="download" table="t_download">
... Field Descriptors ...
<collection-descriptor name="models"
element-class-ref="pal_model"
indirection-table="t_download_pal_model"
>
<fk-pointing-to-this-class column="download_id"/>
<fk-pointing-to-element-class column="model_id"/>
</collection-descriptor>
</class-descriptor>
And going from model -> download...
<class-descriptor class="model" table="t_model">
... Field Descriptors ...
<collection-descriptor name="downloads"
element-class-ref="download"
indirection-table="t_download_pal_model"
>
<fk-pointing-to-this-class column="model_id"/>
<fk-pointing-to-element-class column="download_id"/>
</collection-descriptor>
</class-descriptor>
Okay, that's a simple non-decomposed M:N and you probably know that
already ... That doesn't really help with the single-collection issue at
all.
Idea #2:
How about:
<class-descriptor class="SupportItemI">
<extent-class class-ref="Document"/>
<extent-class class-ref="Download"/>
</class-descriptor>
<class-descriptor class="pal_model" table="t_pal_model">
... Field Descriptors ...
<collection descriptor name="collectionOfSupportItemIs"
element-class-ref="SupportItemI"
indirection-table="t_pal_model_supportitems"
>
<fk-pointing-to-this-class column="model_id"/>
<fk-pointing-to-element-class column="SupportItemID"/>
</collection-descriptor>
</class-descriptor>
<class-descriptor class="download" table="t_download">
... Field Descriptors ...
<collection-descriptor name="models"
element-class-ref="pal_model"
indirection-table="t_download_pal_model"
>
<fk-pointing-to-this-class column="SupportItemID"/>
<fk-pointing-to-element-class column="model_id"/>
</collection-descriptor>
</class-descriptor>
You should be able to keep your object design the same and just modify
the tables a bit so there is one table for both relations... Still
non-decomposed :)
#3:
Implement pal_model_download and pal_model_document as classes,
extending a common class (ModelContents). Then ...
<class-descriptor class="ModelContents">
<extent-class class-ref="pal_model_download"/>
<extent-class class-ref="pal_model_document"/>
</class-descriptor>
<class-descriptor class="pal_model" table="t_pal_model">
... Field Descriptors ...
<collection descriptor name="collectionOfSupportItemIs"
element-class-ref="ModelContents"
>
<inverse-foreignkey field-ref="model_id"/>
</collection-descriptor>
</class-descriptor>
<class-descriptor class="download" table="t_download">
... Field Descriptors ...
<collection-descriptor name="Models"
element-class-ref="pal_model_download"
>
<inverse-foreignkey field-ref="download_id"/>
</collection-descriptor>
</class-descriptor>
<class-descriptor class="pal_model_download"
table="t_pal_model_download">
<field-descriptor name="model_id" ... />
<field-descriptor name="download_id" ... />
<reference-descriptor name="download"
class-ref="download"
>
<foreignkey field-ref="download_id"/>
</reference-descriptor>
<reference-descriptor name="model"
class-ref="model"
>
<foreignkey field-ref="model_id"/>
</reference-descriptor>
</class-descriptor>
This will make the object model a bit harder, since
model.collectionOfSupportItemIs will return ModelContent objects, not
actual Downloads/Documents (i.e decomposed M:N) but you can keep the
existing table stuff.
Others may have better ideas :)
Good Luck,
Rob :)
-----Original Message-----
From: Patrick Scheuerer [mailto:[EMAIL PROTECTED]
Sent: Friday, 2 January 2004 2:56 p.m.
To: OJB Users List
Subject: Mapping Question
Hi,
Please see the attached image of my data model for reference (I'm sorry
for the
attachment but it's kind of complicated to describe the scenario
otherwise. A
picture says more than a thousand words :-) ).
How do I map the relationship between pal_model - download and pal_model
- document? The corresponding value objects (DownloadVO and DocumentVO)
both implement the
Interface SupportItemI.
My PalModelVO has a collection which holds all the SupportItemIs for a
PalModelVO.
How can I map a collection that gets it's data from two m-n
relationships? Can I
specify two indirection tables? Do i have to change my data model?
Any comments and suggestions are welcome.
I wish everybody a peaceful, prosperous and happy new year! Patrick
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