On Feb 18, 2006, at 12:46 PM, Rick Morrision wrote:
Mike,
PG will give back the value of a newly inserted SERIAL value by
calling " SELECT currval('sequencename') ". If this is issued
inside the same transaction as the INSERT, it's race-condition free.
thats good to know. we are pre-executing the sequence in general so
it works out just as well. the bug was that a condition arose, when
you reflected the table and it therefore created a "passive" default
(docs upcoming for this concept...) where this pre-execution wasnt
occuring. you now can specify the column default as anything you
want, not just a sequence, and it still should work, even if its on a
primary key. this works in a more general case than using just
'currval' since the column default doesnt even have to be a sequence.
I believe the reason pyscopg doesn't do this to set
cursor.lastrowid, is
a) - there may be more than one SERIAL column on the row, and no
way to determine which is the "row id"
b) - won't work in autocommit mode
the reason it doesnt work is because by definition, lastrowid is
supposed to return an internal "row id" object, not the primary key
column. But, postgres deprecated OID as of 8.something, and made
it so that tables by default will not have OIDs. they also said,
"dont use OIDs", which I believe is because the OID is not big enough
to encompass the highest actual row number, and some other reasons
you can see if you search the psycopg mailing list.
a couple of links from psycopg:
return only OIDS (I think theyre right, too) :
http://www.initd.org/tracker/psycopg/ticket/29
still waiting for someone to suggest how a lastrowid should be
implemented:
http://article.gmane.org/gmane.comp.python.db.psycopg.devel/2835
im not exactly sure why postgres cant just fix OID, I would think
that rows already have some kind of absolute internal identifier.
*shrug*....
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