Thread: Trigger function returning null
In backend/commands/trigger.c the following can be found:
/* * Trigger protocol allows function to return a null pointer, * but NOT to set the isnull result flag.
*/ if (fcinfo.isnull) ereport(ERROR,
Why?
Regards,
Thomas Hallgren
Thomas Hallgren <thhal@mailblocks.com> writes:
> In backend/commands/trigger.c the following can be found:
> /*
> * Trigger protocol allows function to return a null pointer,
> * but NOT to set the isnull result flag.
> */
> if (fcinfo.isnull)
> ereport(ERROR,
> Why?
Why not?
The real answer is "it's historical and I didn't see any need to
change it". But one could argue that a function returning NULL
doesn't know it's supposed to be a trigger.
regards, tom lane
Thomas Hallgren <thhal@mailblocks.com> writes:
> Perhaps you should either change this behavior or make a note it in
> "Writing Trigger Functions in C"?
Okay, I've changed the text thusly:
diff -r1.35 trigger.sgml
434,435c434,437
< A trigger function must return either <symbol>NULL</> or a
< <structname>HeapTuple</> pointer. Be careful to return either
---
> A trigger function must return either a
> <structname>HeapTuple</> pointer or a <symbol>NULL</> pointer
> (<emphasis>not</> a SQL NULL, that is, do not set isNull true).
> Be careful to return either
regards, tom lane
Tom Lane wrote: >Why not? > >The real answer is "it's historical and I didn't see any need to >change it". But one could argue that a function returning NULL >doesn't know it's supposed to be a trigger. > > The reason I ask is that this behavior just bit me in PL/Java. Triggers returning null didn't work. I've fixed it at my end by simply forcing the isnull to false for triggers. I just wanted to know if there was some deeper thought behind this that could result in side effects. Perhaps you should either change this behavior or make a note it in "Writing Trigger Functions in C"? Even if the documented example use a local isnull, it's not evident that you have to do that. Regards, Thomas Hallgren