Re: Virtual generated columns

Peter Eisentraut <peter@eisentraut.org>

From: Peter Eisentraut <peter@eisentraut.org>

To: jian he <jian.universality@gmail.com>

Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, Dean Rasheed <dean.a.rasheed@gmail.com>

Date: 2025-01-08T16:19:21Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Expand virtual generated columns for ALTER COLUMN TYPE
- 5069fef1cfae 18.0 landed
Eliminate code duplication in replace_rte_variables callbacks
- 363a6e8c6fcf 18.0 landed
Expand virtual generated columns in the planner
- 1e4351af329f 18.0 landed
Virtual generated columns
- 83ea6c54025b 18.0 landed
Additional tests for stored generated columns
- 41084409f635 18.0 landed
Improve generated_stored test
- 44b61efb7928 18.0 landed
- 86749ea3b766 18.0 landed
Fix handling of CREATE DOMAIN with GENERATED constraint syntax
- 84a67725cd11 18.0 landed
Add pg_constraint rows for not-null constraints
- 14e87ffa5c54 18.0 cited
Put generated_stored test objects in a schema
- 894be11adfa6 18.0 landed
Rename regress test generated to generated_stored
- b9ed4969250d 18.0 landed
Small code simplification
- 7ff9afbbd1df 18.0 landed
Remove useless code
- e26d313bad92 18.0 landed
Remove useless initializations
- da2aeba8f533 18.0 landed
doc: Clarify that pg_attrdef also stores generation expressions
- da486d360103 18.0 landed
Clean out column-level pg_init_privs entries when dropping tables.
- 76618097a6c0 17.0 cited
Re-implement the ereport() macro using __VA_ARGS__.
- e3a87b4991cc 13.0 cited

On 11.12.24 07:49, jian he wrote:
> On Fri, Nov 29, 2024 at 6:01 PM Peter Eisentraut <peter@eisentraut.org> wrote:
>> The purpose of check_modified_virtual_generated() for trigger functions
>> written in C.  The prevent someone from inserting real values into the
>> trigger tuples, because they would then be processed by the rest of the
>> system, which would be incorrect.
>>
>> Higher-level languages such as plpgsql should handle that themselves, by
>> preventing setting generated columns in trigger functions.  The presence
>> of check_modified_virtual_generated() is still a backstop for those, but
>> shouldn't really be necessary.
> 
> please check the attached patch.
> * remove check_modified_virtual_generated.
> * using heap_modify_tuple_by_cols in ExecBRInsertTriggers, ExecBRUpdateTriggers
> to overwrite virtual generated columns value to null.
> 
> and it's not complicated.
> so that trigger behavior for stored and virtual will be more aligned

I have integrated that into v11.  I agree it's not complicated and it's 
better to keep the behavior aligned.

I kept the function check_modified_virtual_generated() but now it just 
modifies the tuple, using your code, instead of erroring.  That avoids 
having to write the same code twice.

I don't understand the purpose of the change in pl_exec.c.