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From Andrus Adamchik <and...@objectstyle.org>
Subject Re: Select Query on Table with no Primary Key
Date Thu, 07 Jun 2007 10:44:28 GMT
To give an example - if you have an EMPLOYEE table, you can make an  
assumption that it is highly unlikely that there are two people with  
the same name, born on the same date, and working in the same  
department. On that assumption you can mark these 4 columns as PK in  
the Modeler: FIRST_NAME, LAST_NAME, DATE_OF_BIRTH, DEPARTMENT_ID.

Works well with views or tables (updateable or read-only) on any DB.

Andrus


On Jun 7, 2007, at 1:29 PM, Andrus Adamchik wrote:

> Tore is right - for Cayenne to handle an object (whether read-only  
> on read/write), it needs to know which column or columns uniquely  
> identify each row. Now... you can fake a PK in your model, even if  
> there's none in the db - just select a really unique combination of  
> columns, and mark those columns as the PK in the modeler. I've  
> mapped tables with such "imaginary PK" a lot.
>
> If it is not possible (i.e. duplicate rows are expected to be  
> fetched), you will have to use DataRows.
>
> Andrus
>
>
> On Jun 7, 2007, at 1:04 PM, Tore Halset wrote:
>
>> On Jun 6, 2007, at 16:12 , Dave Merrin wrote:
>>
>>> I'm trying to run a SelectQuery on a table with no primary key.  
>>> Unfortunately it's not working. Can anybody help? I have no  
>>> control over the database so I can't add in primary keys.
>>
>> As you know the PK are essential not only to update a row, but to  
>> make sure a single row maps to a single DataObject in your context.
>>
>> Some database engines do have a unique invisible column. If your  
>> database does this, then perhaps you could map that column as your  
>> primary key? What database engine are you using?
>>
>> Regards,
>>  - Tore.
>>
>
>


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