Re: [HACKERS] How do we find serial types

Thomas G. Lockhart wrote:

>
> > I guess it's too late for 6.4 so hopefully there is already a way to
> > find out whether a field was declared as a serial type.  Am I stuck
> > using some sort of index name hack?
>
> Probably. I did the serial type implementation as a hash of hooks I
> already had in the backend (and at the behest of others, so don't blame
> me too much :). It isn't integrated as well as it could/should be, and
> we should clean this up for v6.5.
>
> It actually might be related to what we will need to do for primary and
> foreign keys, so might get fixed with that stuff. Jan has indicated an
> interest in pursuing some of this through the rules system.

    I'm not sure if the rule system can address serial types as I
    don't know what is required for them. Should a serial type be
    forced  to  use  nextval('serial')  on  INSERT  and  then  be
    forbidden to be touched until DELETE?

    That's not possible with the current  rule  system.  But  the
    force/check  could  be  implemented similar to rewrite rules.
    After parsing we could replace or add the TLE  expression  in
    INSERT  to  be  a  nextval('serial') call if it isn't already
    that. And on UPDATE we could simply throw  an  ERROR  if  the
    serial  type column appears in the targetlist and isn't a Var
    reference to it's own OLD value.   Other  behaviour  is  also
    possible.   Since  I'm  very familiar with screwing around in
    the targetlist from the work in the rule system I would  help
    doing so :-)

    What  I'm  planning  on  the  rule  system  is  to bring back
    attribute checks. I think it would be good to have  an  array
    of  up  to  8  attribute  numbers  instead  of  the one attno
    currently present. Then the actual rule will only  be  fired,
    if  one of the named attributes appears in the targetlist and
    isn't a reference to OLD.same_attr.  Having a rule ON  UPDATE
    will then only add the rule actions, if one of the attributes
    could change at all (attributes not in  the  targetlist  will
    later  be added by the optimizer as Var refs to the OLD tuple
    and thus could never change on this query).

    The next thing required then would be the implementation of a
    RAISE  statement.  This is mostly the same thing as a SELECT,
    but it will use the  final  result  rows  to  produce  elog()
    messages.  Trivial to add.

    After these enhancements, constraints could be implemented by
    adding special rules built from  the  CONSTRAINT  clauses  at
    CREATE  TABLE  time.   The following event/action pairs could
    easily be implemented with the rule system as it already  is.
    The  attribute checks would only suppress stupid-in-fact-noop
    queries to get generated.

    Event:  INSERT to a table
    Action: RAISE an ERROR if column  values  are  outside  of  a
            specified  range  (fixed list of possible values or a
            subselect from a key table).

    Event:  UPDATE to a table
    Action: RAISE an ERROR if new colum values are outside  of  a
            specified  range  (fixed list of possible values or a
            subselect from a key table).

    Event:  DELETE from a referenced key table
    Action: Constraint delete rows in other tables that reference
            the deleted key.

            OR

            RAISE an ERROR telling that the row cannot be deleted
            while it is referenced.

    Event:  UPDATE on a referenced key table where the values  of
            the key fields change
    Action: Constraint delete rows in other tables that reference
            the old key.

            OR

            RAISE an ERROR telling that the key value  cannot  be
            changed while it is referenced.

    Isn't  that all (or already more) we need for FOREIGN KEY and
    ON DELETE CASCADE?

    Even  if  it  is  possible  with  the  rule  system,  to  let
    references  to a key table follow on updates, such a scenario
    isn't easy to setup during CREATE TABLE from  the  CONSTRAINT
    clauses.  This  must  be  setup  manually  if  it  is  really
    required.


Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#======================================== jwieck@debis.com (Jan Wieck) #