Trigger function returning null

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

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

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