Re: Updatable Cursors, CTID, and Views

-----Original Message-----
From: Janet Borschowa [mailto:borschow@roguewave.com]
Sent: Wednesday, July 28, 2004 9:18 AM
To: Mark Dexter; pgsql-odbc@postgresql.org
Cc: 'Dave Page'
Subject: RE: [ODBC] Updatable Cursors, CTID, and Views

Hi,

I believe that Hiroshi probably used the ctid because views are not updateable. It looks like you have to do extra work to update a view and in that case, I'm not sure how a cursor in the driver would be implemented as there needs to be a way to uniquely identify a row which is why Hiroshi used the ctid column.

 

From the PostgreSQL docs for the SQL statement "CREATE VIEW":

Description

CREATE VIEW defines a view of a query. The view is not physically materialized. Instead, the query is run every time the view is referenced in a query.

...

Notes

Currently, views are read only: the system will not allow an insert, update, or delete on a view. You can get the effect of an updatable view by creating rules that rewrite inserts, etc. on the view into appropriate actions on other tables. For more information see CREATE RULE.

Sorry I can't be of help but I don't know if or how you could define a view with a ctid column and appropriate rules to enable the driver to use a cursor on it.

 

========================
Janet Borschowa
Software Engineer, Database Products                       
Rogue Wave Software, a QUOVADX(tm) Division
(541) 753-1931   FAX: (541) 757-4630
mailto:borschow@roguewave.com  http://www.roguewave.com

-----Original Message-----
From: Dave Page [mailto:dpage@vale-housing.co.uk]
Sent: Wednesday, July 28, 2004 12:29 AM
To: Mark Dexter; pgsql-odbc@postgresql.org
Subject: Re: [ODBC] Updatable Cursors, CTID, and Views

 

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From: pgsql-odbc-owner@postgresql.org [mailto:pgsql-odbc-owner@postgresql.org] On Behalf Of Mark Dexter
Sent: 27 July 2004 23:26
To: pgsql-odbc@postgresql.org
Subject: [ODBC] Updatable Cursors, CTID, and Views

From a prior posting on November 5, 2002, I found this text regarding the use of CTID in the ODBC driver:

The driver uses CTID and OID to implement updatable cursors. Please turn off the *Updatable cursors* DSN option if you don't like the behavior. regards, Hiroshi Inoue

I am having a problem where I need to use updatable cursors with views.  It appears that the ODBC driver is trying to use the CTID and OID columns and that views don't have these columns.  Is it possible to use updatable cursors with views via the PostgreSQL ODBC driver?

 Not from what Hiroshi has said (he wrote the cursor code). I imagine he used CTID because it needs to be able to locate the exact version of each row - in a view that won't work because ctid don't exist. I guess you could try adding it to your view definition though that will probably only work for single table views of course.

I'm not sure why he would have used oid given that it may not exist even in a table...

Regards, Dave.