Hi John,
as mentioned to Andrus I'm going with the setting primary keys on
columns. I actually found some documentation for the database which said
which columns make the rows unique. This keeps things relatively simple.
BTW. also tried some prefetching today....cool stuff. I got some code
down from 8 seconds down to 3 seconds.
Cheers for the help... support is the reason I'm using Cayenne rather
than Hibernate.
Dave
John wrote:
Hello Dave,
You said you use a view and you will NOT modify the data, then try this:
Your View name : MyView.
--------------------------------------------------------------------------------------------------------------------------
create another view call MyViewWithPK
-------------------------------------------------
SELECT e.* , (SELECT COUNT(*) FROM MyView e2 WHERE e2.name <= e.name )
AS rownumber
FROM MyView e
// remember that name must be included in the view MyView
// remember that this technique is slow, but i suppose this is your
last problem :)
---------------------------------------------------------------------------------------------------------------------------
let me know if this work :)
Sako
Signature IT-Consult Armainak Sarkis
----- Original Message ----- From: "Dave Merrin"
<[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Thursday, June 07, 2007 3:36 PM
Subject: Re: Select Query on Table with no Primary Key
Hi Andrus,
I was playing about with putting in my own EntityResolver. For now
I'm going to take your approach and see how I get on.
Cheers,
Dave
Andrus Adamchik wrote:
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.
