On Wed, Aug 10, 2011 at 8:38 AM, Mauro <maurogdo@yahoo.com.br> wrote:
> Hi, good morning list
> I'm writing a generic trigger in plpgsql to provide a system log to my
> system, but I'm stopped with the folow problem:
> Example:
> TABLE STRUCT:
> table1
> fldA VARCHAR
> fldB VARCHAR
> fldC VARCHAR
> FUNCTION:
> DECLARE
> myrecord RECORD; -- record that will be storing field names from
> internal postres tables
> fieldtest NAME; -- actual field name parsing
> BEGIN
> -- Generic function to automatize the log of changes
>
> -- 1st, discover the field names from a table
> FOR myrecord IN
> SELECT
> att.attname
> FROM
> pg_attribute att,
> pg_class cls
> WHERE
> cls.oid = att.attrelid
> AND att.attnum > 0
> AND cls.relname = TG_RELNAME limit 1
> LOOP
> -- storing the actual field name
> fieldtest = myrecord.attname;
>
> /*
> Here I'd like to do a parse in the 'fieldtest' variable to teste if
> the new value is diferent of the old value. The problem is:
> Variable name: fieldtest
> Variable content: fldA
> How I can test the two records (new and old)?
> -- new.fieldtest = fieldtest is not a field name to new record
> -- new."fieldtest" = fieldtest is not a field name to new record
> -- new.(fieldtest) = plpgsql can not do a parser in this
> -- 'new.' || fieldtest = this is a string and can not be evaluate
> */
>
>
> END LOOP;
>
> -- Returning
> RETURN NEW;
> END;
This is a FAQ. See archives (for example, here:
http://www.mail-archive.com/pgsql-hackers@postgresql.org/msg182249.html).
A couple quick points:
*) plpgsql does not directly support record access like that.
*) you can compare new vs old directly without breaking down to fields
*) record into hstore is probably the easiest approach to dynamic
access of record fields by field name -- then you can drop the catalog
query
merlin
