Re: A question about rules

On Sun, Jan 19, 2020 at 08:52:36AM -0800, Adrian Klaver wrote:
> On 1/19/20 2:32 AM, stan wrote:
> Please post to list also.
> Ccing list.
>
> > On Sat, Jan 18, 2020 at 08:56:06AM -0800, Adrian Klaver wrote:
> > > On 1/18/20 8:53 AM, stan wrote:
> > > > So, I just discovered the rules system. As I understand it, it can be used
> > > > to rewrite queries before they are passed to the query processor.
> > > >
> > > > I was wondering if I could use this to resolve a long standing frustration
> > > > of mine. I often need to declare a column as NON NULL, and create a
> > > > trigger/function to auto populate it with something more complex than a
> > > > simple sequence. This need arises fairly often for me, and I would like to
> > > > come up with a good way to implement this.
> > >
> > > Stay away from rules, they will only drive you to distraction. Stick with
> > > triggers they are a lot easier to understand and implement.
> > >
> >
> > I use triggers quite a bit. My issue is that if I have a column defined as
> > NOT NULL, and assign a trigger that fires a function to auto populate this
> > column if the user (input form) does not. The NOT NULL constraint is
> > checked BEFORE the trigger can fire, which means that I cannot properly
> > provide data integrity.
> >
>
> I don't know that this changes with rules. In other words I believe
> constraints are checked first with either rules/triggers. Someone else will
> need to confirm this.
>
> A work around is to supply a dummy DEFAULT for the the NOT NULL column e.g.
> for a varchar column the string 'NOT NULL'. Test for this in the trigger and
> take the appropriate action. Or accept the reality which is, you are
> allowing NULL input to the column and take away the NOT NULL constraint and
> look for NULL or empty string input and take the appropriate action.
>

Thanks, the dea of a default is an interesting one. I will consider that
solution.
--
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
-- Benjamin Franklin