Hi all,

Here is the solution I ended up in using to solve the problem.

a. Created a copy_blob function.

CREATE OR REPLACE FUNCTION copy_blob(p_blobId OID)
RETURNS OID AS $$
DECLARE
v_NewOID OID;
BEGIN
SELECT lo_create(-1) INTO v_NewOID;

delete from pg_largeobject where loid = v_NewOID;

INSERT INTO pg_largeobject (loid, pageno, data)
SELECT v_NewOID, pageno, data
FROM pg_largeobject
WHERE loid = p_blobId;

RETURN v_NewOID;
END;
$$ LANGUAGE plpgsql;

2. selected the OID from table_a;

3. select copy_blob(OID from table_a);

4. insert into table_b
(
id,
filename)
values
(
nextval('table_b_id_seq'),
v_NewOID
);

Works well so far.

John

On Fri, Oct 17, 2008 at 1:37 PM, John Skillings wrote:

Hi Diogo,

Thanks for your response. However, my requirement is to have two separate
copies. Think about table_a being the original copy, and table_b holding
the backup copy.

Inserting the OID from table_a to table_b will not make the backup copy.

Best Regards,

John


On Fri, Oct 17, 2008 at 12:32 PM, Diogo Biazus wrote:


Em 17/10/2008, às 18:18, John Skillings escreveu:


Hi all,
I am trying to copy blobs between two tables and need help on the best
way to get this done. My requirement is that the both the tables maintain
their own copy of the large object, instead of sharing the OID.

I created two tables:

create table table_a
(id bigserial not null,
filename oid);

create table table_b
(id bigserial not null,
filename oid);

In one of the tables, I uploaded a file from the filesystem.

INSERT INTO table_a (id, filename)
VALUES ( nextval('table_a_id_seq'),
lo_import('C:/applications/largeobj.zip'));

The record is inserted, and I verified the record's integrity by:

SELECT lo_export(filename, 'C:/applications/largeobj.zip_copy.zip') FROM
table_a;

Question
----------------
Now to make a copy of the object from table to table_a to table_a.
Currently I am exporting the file from table_a to the file system, and again
doing an import into table_b. However, in a large application, I find this
workaround not practical because of the volume of the records, and also the
size of the file (binary object). My ideal solution to do an insert of the
values from table_a into table_b directly.

So, what is best way to create a copy of this LOB from table_a to
table_b?
You can copy only the oid, You don't need to have another copy of the same
file in the database, if you copy only the oid you'll have another reference
to the same file.

So a simple
INSERT INTO table_a SELECT * FROM table_b;
will do the trick in your example.

--
Diogo Biazus
diogob@gmail.com
http://www.softa.com.br
http://www.postgresql.org.br

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