Convert a bytea column to OID while retaining values

Question

I\'m trying to alter a bytea column to have type oid and still retain the values.

I have tried using queries like:

ALTER TA         


        

Answer 1

Postgres 9.4 adds a built-in function for this:

lo_from_bytea(loid oid, string bytea)

From the release notes:

• Add SQL functions to allow [large object reads/writes][12] at arbitrary offsets (Pavel Stehule)

For older versions, this is more efficient than what has been posted before:

CREATE OR REPLACE FUNCTION blob_write(bytea)
  RETURNS oid AS
$func$
DECLARE
   loid oid := lo_create(0);
   lfd   int := lo_open(loid, 131072);  -- = 2^17 = x2000
   -- symbolic constant defined in the header file libpq/libpq-fs.h
   -- #define   INV_WRITE   0x00020000
BEGIN
   PERFORM lowrite(lfd, $1);
   PERFORM lo_close(lfd);
   RETURN loid;
END
$func$  LANGUAGE plpgsql VOLATILE STRICT;

The STRICT modifier is smarter than handling NULL manually.

SQL Fiddle.

More in this related answer:

• Understanding cast from bytea to oid