From: | Steve Howe <howe(at)carcass(dot)dhs(dot)org> |
---|---|
To: | |
Cc: | pgsql-interfaces(at)postgresql(dot)org, pgsql-odbc(at)postgresql(dot)org |
Subject: | Re: [ODBC] BLOB handling compatibility with PostgreSQL |
Date: | 2005-12-06 19:29:18 |
Message-ID: | 4395E68E.3000707@carcass.dhs.org |
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Thread: | |
Lists: | pgsql-interfaces pgsql-odbc |
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
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