Question

Get Column value from PostgreSQL Trigger

Asked by: jpadkins49

All,
I currently need to implement a trigger in PostgreSQL that executes on the update of a row that executes the following function name in my database:

Function_Set_Authorized("ID Parameter From Update Trigger")
The problem that I am having is how to get the value of my ID column from the updated row to my trigger. Is there a way to read this value into a variable and pass it to the execution of the function above. I need the ID to tell the function which record to update. This is easily apparent to me in SQL Server by using the following:
DECLARE @ID int
Select @ID = ID from Inserted

Can someone provide me with an example on how to get the ID of the column in the trigger and pass it to my function.

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Asked On
2009-09-11 at 10:22:32ID24725265
Tags

Postgre

Topic

PostgreSQL Database

Participating Experts
3
Points
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Comments
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Answers

 

by: cminearPosted on 2009-09-11 at 12:22:33ID: 25312662

PostgreSQL provides the record OLD for UPDATE and DELETE triggers, and NEW for INSERT and UPDATE triggers.  See the bottom of http://www.postgresql.org/docs/8.4/interactive/trigger-definition.html

The below code should provide a simple example of the function.  You would create your trigger to use 'do_set_authorized', and that function will perform the 'Function_Set_Authorized'.  

If 'Function_Set_Authorized' is already a trigger function, then just use 'NEW.id' (or 'OLD.id' if id will never change for a given record) where you need to use in it 'Function_Set_Authorized'.

CREATE FUNCTION do_set_authorized() RETURNS TRIGGER AS $PROC$
BEGIN
  Function_Set_Authorized(NEW.id);
  RETURN NEW;
END;
$PROC$ LANGUAGE plpgsql;
 
--- OR ---
 
CREATE FUNCTION Function_Set_Authorized() RETURNS TRIGGER AS $PROC$
DECLARE
  local_id integer := NEW.id
BEGIN
   ... code using local_id ...
END;
$PROC$ LANGUAGE plpgsql;

                                              
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by: earthman2Posted on 2009-09-12 at 17:21:18ID: 25318499

http://www.postgresql.org/docs/8.4/interactive/plpgsql-trigger.html#PLPGSQL-TRIGGER-EXAMPLE

CREATE FUNCTION do_set_authorized() RETURNS TRIGGER AS $$
BEGIN
  Function_Set_Authorized( OLD.id );
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;


CREATE TRIGGER your_trigger_name_001 BEFORE UPDATE
    ON your_table_name  FOR EACH ROW
    EXECUTE PROCEDURE do_set_authorized();

 

by: jpadkins49Posted on 2009-09-14 at 06:24:18ID: 25325085

All,

Thanks for the help so far. I have encountered an error. It says that the max stack depth has been exceeded when I perform an update on accruals. Below is the code for the trigger and function. Is it possible that I have written a recursive function that is not ending. Any help is greatly appreciated.

-- Trigger: proc on accrual
 
-- DROP TRIGGER proc ON accrual;
 
CREATE TRIGGER proc
  BEFORE INSERT OR UPDATE
  ON accrual
  FOR EACH ROW
  EXECUTE PROCEDURE function_round_comptime();
 
 
-- Function: function_round_comptime()
 
-- DROP FUNCTION function_round_comptime();
 
CREATE OR REPLACE FUNCTION function_round_comptime()
  RETURNS trigger AS
$$
DECLARE
  
BEGIN
                UPDATE accrual set amount = round((round(amount/60/60 * 4,0) / 4),2) where id = OLD.id and accrual_policy_id in(7);
           
           
       
        RETURN NULL;
END;
 -- Insert or update the summary row with the new values.
       
 
$$
  LANGUAGE 'plpgsql' VOLATILE
  COST 100;
ALTER FUNCTION function_round_comptime() OWNER TO postgres;
                                              
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by: ivanovnPosted on 2009-09-14 at 07:19:23ID: 25325685

Well you're running a before update trigger on a table which then tries to update that same table. I am assuming that this fires the trigger again, which tries to update, which fires the trigger, which tries to update, which fires the trigger, and so on.

 

by: cminearPosted on 2009-09-14 at 07:20:24ID: 25325694

Yes, you are causing a recursion.  On the page link I gave before, read the 3rd to last paragraph (starting "If a trigger function...").   You are performing an UPDATE on accrual table, your trigger does what?  Performs an UPDATE on the accrual table, which causes another trigger.

I believe you should change your function_round_comptime to something like below.  Basically, you are changing the value of the NEW record before it is stored in the database.

Of course, with the way this function is defined, it is likely that you want this set only with INSERTs.  Currently, with UPDATEs that don't alter the 'amount' value, it would still be divided by 60 twice, thus altering the value unnecessarily.  You could do a check of whether the OLD and NEW value are different as part of the conditional check before altering the value.  I gave an example below.

In other words, just double-check that it's doing what you want.

-- Function: function_round_comptime()
 
-- DROP FUNCTION function_round_comptime();
 
CREATE OR REPLACE FUNCTION function_round_comptime()
  RETURNS trigger AS
$$
DECLARE
  
BEGIN
  IF NEW.accrual_policy_id in (7) THEN
    NEW.amount := round((round(NEW.amount/60/60 * 4,0) / 4),2) ;
  END IF;
 
  RETURN NULL;
END;
 -- Insert or update the summary row with the new values.
$$
  LANGUAGE 'plpgsql' VOLATILE
  COST 100;
 
 
 
--- Alternate function guts
 
  IF (TG_OP = 'INSERT' OR OLD.amount <> NEW.amount) 
     AND NEW.accrual_policy_id in (7) THEN
    NEW.amount := round((round(NEW.amount/60/60 * 4,0) / 4),2) ;
  END IF;
                                              
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by: cminearPosted on 2009-09-14 at 07:24:27ID: 25325756

I missed one other change.  Instead of "RETURN NULL;", it should be "RETURN NEW;", so that the modified NEW record is stored in the database.  See example 38-3 here: http://www.postgresql.org/docs/8.4/static/plpgsql-trigger.html

 

by: jpadkins49Posted on 2009-09-23 at 12:10:00ID: 31627666

Thanks for all the help.

20120131-EE-VQP-002

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