Customizing 1:1 querys like customized collection queries | second trail

[jo...@on-ergy.de]

Hello OJB-Users,
I haven't get any feedback on this email yet, so I try it once more.
The problem is that the Informations from the Foreign key are Primary-Key 
+ hardcoded String.
How can I add the hardcoded String to my 1:1 reference?
For 1:n, it's no Problem, because I can add the String to the Query in an 
QueryCustomizer

----------------------------------------------------------------------------------------------------------------------

I have even started using OJB and so far all works fine :o) (1:1, 1:n...)
I would be pleased when you can help me with my first Problem.

I'm looking for an solution like 'Customizing collection queries' 
descriped in the Guide 'advanced O/R technique' for 1:1 references.

A short example:

I have multible tables (named parts, driver...) and for each entry of a 
table i can reference to ONE entry of a table named memo across the 
primary-key as foreign key in the memo-table.
To have a unique key, I musst save a second value in the memo-table to 
know from which table the foreign-key comes. This value is a String and is 
hardcoded in the software.
For table parts i save = "part" in the table Memo field parentTable
For table driver i save = "driv" in the table Memo field parentTable

Now, when I'm loading the memo to an item of the parts-table, I want' only 
load the memo where in table Memo parentTable="part"

With a 1:n, thats no Problem, because I can work with the query-customizer 
like this
################################
<inverse-foreignkey field-ref="parentObjId"/>
   <query-customizer
   class="de.on_ergy.lakon.data.QueryCustomizerLakonImpl">
   <attribute
   attribute-name="parentTable"
   attribute-value="TEILSTAM"
   />
</query-customizer>
################################

There I can add the value "TEILSTAM" to the Query with the written 
QueryCustomizerLakonImpl

But how can I realize this with 1:1 ??

Thank you very very much for your help.

Best Wishes

Josef Wagner
/Germany

Re: Customizing 1:1 querys like customized collection queries | second trail

[Armin Waibel <ar...@apache.org>]

Hi Josef,

think this is not possible, because OJB handle 1:1 references different 
from 1:n. 1:1 references are identity based (the main object knows the 
PK values of the referenced object), so there is no need to use a 
QueryCustomizer.

The 1:1 reference point from named parts, driver... to Memo - correct?
In your Memo table an entry/row is only unique when the PK is composed 
of the PK of the main table (driver, ...) and a String field ("driv", 
...)? If this is true, you have to declare both fields as PK in the 
class-descriptor of the Memo class and the 1:1 reference in e.g. Driver 
class look like this

<reference-descriptor
     name="memo"
     class-ref="Memo"
     proxy="false"
     auto-retrieve="true"
     auto-update="true"
     auto-delete="false">
         <foreignkey field-ref="fkMemoId"/>
         <foreignkey field-ref="fkMemoString"/>
</reference-descriptor>

Both FK fields are needed in Driver,...

If I it get it wrong, could you describe more detailed with 
class-descriptor examples?

regards,
Armin


josef.wagner@on-ergy.de wrote:
> Hello OJB-Users,
> I haven't get any feedback on this email yet, so I try it once more.
> The problem is that the Informations from the Foreign key are Primary-Key 
> + hardcoded String.
> How can I add the hardcoded String to my 1:1 reference?
> For 1:n, it's no Problem, because I can add the String to the Query in an 
> QueryCustomizer
> 
> ----------------------------------------------------------------------------------------------------------------------
> 
> I have even started using OJB and so far all works fine :o) (1:1, 1:n...)
> I would be pleased when you can help me with my first Problem.
> 
> I'm looking for an solution like 'Customizing collection queries' 
> descriped in the Guide 'advanced O/R technique' for 1:1 references.
> 
> A short example:
> 
> I have multible tables (named parts, driver...) and for each entry of a 
> table i can reference to ONE entry of a table named memo across the 
> primary-key as foreign key in the memo-table.
> To have a unique key, I musst save a second value in the memo-table to 
> know from which table the foreign-key comes. This value is a String and is 
> hardcoded in the software.
> For table parts i save = "part" in the table Memo field parentTable
> For table driver i save = "driv" in the table Memo field parentTable
> 
> Now, when I'm loading the memo to an item of the parts-table, I want' only 
> load the memo where in table Memo parentTable="part"
> 
> With a 1:n, thats no Problem, because I can work with the query-customizer 
> like this
> ################################
> <inverse-foreignkey field-ref="parentObjId"/>
>    <query-customizer
>    class="de.on_ergy.lakon.data.QueryCustomizerLakonImpl">
>    <attribute
>    attribute-name="parentTable"
>    attribute-value="TEILSTAM"
>    />
> </query-customizer>
> ################################
> 
> There I can add the value "TEILSTAM" to the Query with the written 
> QueryCustomizerLakonImpl
> 
> But how can I realize this with 1:1 ??
> 
> Thank you very very much for your help.
> 
> Best Wishes
> 
> Josef Wagner
> /Germany

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