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.
