From: | Jonathan Rogers <jrogers(at)emphasys-software(dot)com> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Determining table change in an event trigger |
Date: | 2016-08-25 00:27:46 |
Message-ID: | cea4afba-a28e-ee4f-9001-3828935ac6f8@emphasys-software.com |
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Lists: | pgsql-general |
On 08/24/2016 12:58 AM, Alvaro Herrera wrote:
> Jonathan Rogers wrote:
>> I am trying to use an event trigger to do something when a column
>> changes. I can declare an event trigger "ON sql_drop WHEN TAG IN ('ALTER
>> TABLE')" to get dropped columns. However, I can't figure out any good
>> way to determine when a column has been added or altered.
>>
>> I can declare an event trigger "ON ddl_command_end WHEN TAG IN ('ALTER
>> TABLE')" but that gets unwanted events such as disabling triggers on a
>> table. Function pg_event_trigger_ddl_commands() returns rows with column
>> "command" of type "pg_ddl_command" which contains "a complete
>> representation of the command, in internal format." According to the
>> docs, this cannot be output directly, but it can be passed to other
>> functions to obtain different pieces of information about the command.
>> However, I cannot find any other functions which operate on the type
>> pg_ddl_command. Am I missing something? Is the documentation lacking?
>
> Yeah, that type can only be processed by C functions. You'd need to
> write a C function to examine the structure and see whether it matches
> what you need.
>
OK, thanks for the explanation. It seems like the docs should make it
clear that the "other functions" are not included.
--
Jonathan Rogers
Socialserve.com by Emphasys Software
jrogers(at)emphasys-software(dot)com
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