On 03/19/2014 12:48 PM, François Beausoleil wrote:
Hi all!
Cross-posted from https://dba.stackexchange.com/questions/61271/how-to-access-new-or-old-field-given-only-the-fields-name
I'm writing a validation trigger. The trigger must validate that the sum of an array equals another field. Since I have many instances of this validation, I want to write a single procedure and create multiple triggers, each with a different set of fields to check.
For example, I have the following schema:
CREATE TABLE daily_reports(
start_on date
, show_id uuid
, primary key(start_on, show_id)
-- _graph are hourly values, while _count is total for the report
, impressions_count bigint not null
, impressions_graph bigint[] not null
-- interactions_count, interactions_graph
-- twitter_interactions_count, twitter_interactions_graph
);
The validation must confirm that impressions_count = sum(impressions_graph).
I'm stuck because I don't know how to dynamically access a field from NEW from within plpgsql:
CREATE FUNCTION validate_sum_of_array_equals_other() RETURNS TRIGGER AS $$
DECLARE
total bigint;
array_sum bigint;
BEGIN
-- TG_NARGS = 2
-- TG_ARGV[0] = 'impressions_count'
-- TG_ARGV[1] = 'impressions_graph'
-- How to access impressions_count and impressions_graph from NEW?
RETURN NEW;
END
$$ LANGUAGE plpgsql;
CREATE TRIGGER validate_daily_reports_impressions
ON daily_reports BEFORE INSERT OR UPDATE
FOR EACH ROW EXECUTE
validate_sum_of_array_equals_other('impressions_count', 'impressions_graph');
I tried http://www.postgresql.org/docs/9.1/static/plpgsql-statements.html#PLPGSQL-STATEMENTS-EXECUTING-DYN by doing EXECUTE 'SELECT $1 FROM NEW' INTO total USING TG_ARGV[0], but PL/PGsql complains that NEW is an unknown relation.
Well two things:
1) From the above link:
Note that parameter symbols can only be used for data values — if you
want to use dynamically determined table or column names, you must
insert them into the command string textually. For example, if the
preceding query needed to be done against a dynamically selected table,
you could do this:
So:
Instead of 'SELECT $1 '.. use 'SELECT ' || TG_ARGV[0] || ..
2) Use NEW outside the quotes.
So:
'FROM ' NEW.*
I am specifically targeting PostgreSQL 9.1.
Thanks for any hints!
François Beausoleil
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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