Обсуждение: Evaluate arbitrary expression on tuple inside trigger function?

Hi all

I'm trying to hack a trigger function to evaluate an expression on the
tuple that the trigger has been fired for, kinda like a check
constraint. I looked at ExecRelCheck in execMain.c which does
more-or-less what I want to do, and I have the parsed node tree all
ready to go. The problem that I'm facing is that ExecRelCheck uses a
passed in EState to set up the executor in the right mode, and with
the right memory context, but the EState doesn't get passed in to the
trigger function, and I can't see anything obvious hanging off the
TriggerData that does get passed in that would give me access to it.

Can anyone either point me to where I might be able to get a handle on
the current EState, or otherwise recommend a way forward?

Thanks

Tom

On Mon, Jul 29, 2013 at 12:59:27PM +0930, Tom Dunstan wrote:
> I'm trying to hack a trigger function to evaluate an expression on the
> tuple that the trigger has been fired for, kinda like a check
> constraint. I looked at ExecRelCheck in execMain.c which does
> more-or-less what I want to do, and I have the parsed node tree all
> ready to go. The problem that I'm facing is that ExecRelCheck uses a
> passed in EState to set up the executor in the right mode, and with
> the right memory context, but the EState doesn't get passed in to the
> trigger function, and I can't see anything obvious hanging off the
> TriggerData that does get passed in that would give me access to it.
> 
> Can anyone either point me to where I might be able to get a handle on
> the current EState, or otherwise recommend a way forward?

I doubt there's a clean way to grab the parent estate.  Creating a local
estate in your trigger function does work.  Compare how copy.c creates one for
some relatively-narrow purposes.

-- 
Noah Misch
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