Re: [ODBC] BLOB handling compatibility with PostgreSQL

[Steve Howe <howe(at)carcass(dot)dhs(dot)org>]

Tom Lane wrote:

> Ludek Finstrle <luf(at)pzkagis(dot)cz> writes:
>  
>
> > I don't want to reinvent the wheel.
> >    
>
> Why do you feel a need to distinguish the domain from its underlying
> type on the client side?  They're the same as regards representation
> and so on.
>
> The reason for the backend change was that client-side drivers (such as
> JDBC and ODBC) want to know the underlying datatype so that they know
> what representation to use etc.  Distinguishing domains made their job
> harder not easier.
>  
>
> If you want an add-on datatype that is really different from OID, then
> make a real datatype (CREATE TYPE).  You can still piggyback on OID as
> the representation type --- steal its I/O functions and so on.
>  
A clear example situation in here is how to be able to distinguish a 
large object field. The ODBC driver, for instance, uses the 'lo' type, 
which is the same as an oid (Large Object).

I ran into exactly the same situation as I wrote the pgExpress driver 
for Vita Voom Software: while declaring a domain looks like the clear 
choice, the original type's oid would be returned by the pq_ftype() 
function. So I based my solution more or less like this post by Hiroshi 
Saito:

http://www.mail-archive.com/pgadmin-hackers(at)postgresql(dot)org/msg01390.html

... and asked the users to create the 'lo' type that way, which would 
create a real type, just like Tom suggests.

For more details on how it was implemented on the pgExpress, please 
check kits documentation:
http://www.vitavoom.com/Products/pgExpress_Driver/docs/advanced_features.html#large_objects_declaration

Best regards,
Steve Howe