Deadline rule date input after now

Question

Hi I'm trying to find a way to ensure deadlines inputted are later than the current time and date. Currently I'm attempting this with a rule.

CREATE OR REPLACE RULE "DeadlineInput" AS
    ON INSERT TO "ComLog"
   WHERE new."Deadline" < now() DO INSTEAD  SELECT "ThrowError"('New deadline must be after current time'::bpchar) AS "ThrowError";
COMMENT ON RULE "DeadlineInput" ON "ComLog" IS 'Ensures deadline input is after the current time.';

I'm using a separate function to try to throw an error as when I tried to do it within the Rule it failed as the language was wrong. The following is my function.

-- Function: "ThrowError"(character)

-- DROP FUNCTION "ThrowError"(character);

CREATE OR REPLACE FUNCTION "ThrowError"("ErrorString" text)
  RETURNS void AS
$BODY$

BEGIN

    RAISE EXCEPTION '%', "ErrorString";

END;

$BODY$
  LANGUAGE plpgsql IMMUTABLE
  COST 100;
ALTER FUNCTION "ThrowError"(character)
  OWNER TO reuben;

This always produces the error message regardless of the date and i don't know why. As a side question is there a way to make the string passed to my function contain the current time. Something like "ThrowError"('New deadline must be after current time %' now())

Thanks

Answer 1

Here's what the current manual says in Rules Versus Triggers:

If checks for valid values are required, and in the case of an invalid value an error message should be generated, it must be done by a trigger.

Consider implementing the check in a trigger, not a rule. The trigger is the perfect tool for the job in your case. On the other hand, it is a known fact that rules are touchy and much harder to master.