Обсуждение: A question about trigger fucntion syntax

Good morning (at least is is morning East Coast USA time).

I am trying to create a function to validate an attempted record 
insert, and I am having a hard time coming up with syntax that
is acceptable.

Here is the scenario I have a table that has (among other items) employee_key
and work_type_key (both integer FOREIGN KEYS). Then I have another table
that has the following structure:

CREATE  TABLE permitted_work (
    employee_key       integer ,
    work_type_key      integer ,
    permit             boolean DEFAULT FALSE NOT NULL ,
    modtime     timestamptz DEFAULT current_timestamp ,
    FOREIGN KEY (employee_key) references
    employee(employee_key) ,
    FOREIGN KEY (work_type_key) references
    work_type(work_type_key) ,
    CONSTRAINT permit_constraint UNIQUE
            (employee_key , work_type_key)
    );

 What I think I need to do is create a function that is fired on an insert,
 or update to the 1st table that verifies that there is an existing row in
 permitted_work that matches the combination of employee_key AND
 work_type_key AND has the value TRUE in the permit column.

 First does this seem to be a good way to achieve this constraint? If not,
 I am open to suggestions as to other ways to address this  requirement. 

 If it does, could someone give me a little help with th syntax of the
 needed function ??

 Thanks for your time helping me with this.



-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin

On Sun, Aug 11, 2019 at 08:56:13AM -0400, stan wrote:
> Good morning (at least is is morning East Coast USA time).
> 
> I am trying to create a function to validate an attempted record 
> insert, and I am having a hard time coming up with syntax that
> is acceptable.
> 
> Here is the scenario I have a table that has (among other items) employee_key
> and work_type_key (both integer FOREIGN KEYS). Then I have another table
> that has the following structure:
> 
> CREATE  TABLE permitted_work (
>     employee_key       integer ,
>     work_type_key      integer ,
>     permit             boolean DEFAULT FALSE NOT NULL ,
>     modtime     timestamptz DEFAULT current_timestamp ,
>     FOREIGN KEY (employee_key) references
>     employee(employee_key) ,
>     FOREIGN KEY (work_type_key) references
>     work_type(work_type_key) ,
>     CONSTRAINT permit_constraint UNIQUE
>             (employee_key , work_type_key)
>     );
> 
>  What I think I need to do is create a function that is fired on an insert,
>  or update to the 1st table that verifies that there is an existing row in
>  permitted_work that matches the combination of employee_key AND
>  work_type_key AND has the value TRUE in the permit column.
> 
>  First does this seem to be a good way to achieve this constraint? If not,
>  I am open to suggestions as to other ways to address this  requirement. 
> 
>  If it does, could someone give me a little help with th syntax of the
>  needed function ??
> 
>  Thanks for your time helping me with this.

BTW, here is what I Ave tried.

CREATE OR REPLACE FUNCTION check_permission()
  RETURNS trigger AS
$BODY$
BEGIN
    SELECT 
        permit
    FROM
        permitted_work
    WHERE
        NEW.employee_key = OLD.employee_key
    AND
        NEW.work_type_key = OLD.work_type_key
        
   RETURN permit;
END;
$BODY$
LANGUAGE PLPGSQL;

and when I try to insert it I get a syntax error at the RETURN

-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin

I trimmed this thread quite a bit.

Thanks to the help I have received, I am making progress. I have looked a the
recommended documentation, and I believe I am close. I have utilized the
"debugging printf" capability here. Here is where I am. I have the following
function create.


DROP TRIGGER validate_task_trig ON task_instance ;

DROP FUNCTION check_permission() ;


CREATE FUNCTION check_permission()
RETURNS trigger AS $$
DECLARE _permit boolean;
BEGIN
        SELECT
                permit INTO _permit
        FROM
                permitted_work
        WHERE
                NEW.employee_key = OLD.employee_key
        AND
                NEW.work_type_key = OLD.work_type_key;
        RAISE NOTICE 'New employee_id % NEW.work_type_key % _permit = %', 
            NEW.employee_key ,
            NEW.work_type_key ,
            _permit ;
        if NOT _permit THEN
                RAISE NOTICE 'No permission record';
                RAISE EXCEPTION 'No permission record';
    ELSE
                RAISE NOTICE 'Found Permission Record';
        END IF;
        if _permit = FALSE THEN
                RAISE NOTICE 'Permission Denied';
    ELSE
                RAISE NOTICE 'Permission Granted';
        END IF;

        return NEW;
END;
$$ 
LANGUAGE PLPGSQL;

CREATE TRIGGER validate_task_trig BEFORE INSERT OR UPDATE ON task_instance
    FOR EACH ROW EXECUTE FUNCTION check_permission();


Now the issues, currently seems to be that nothing is getting assigned to
_permit. Here is the output of a run with 0 records in the permitted_work
table.

NOTICE:  New employee_id 1 NEW.work_type_key 8 _permit = <NULL>
NOTICE:  Found Permission Record
NOTICE:  Permission Granted
INSERT 0 1

so it appears that nothing is getting assigned to _permit. Also should I be
checking for _permit as NOT NULL in the first if clause?

Thanks for all the had holding on this. Brand new application for me.

-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin

On Sun, Aug 11, 2019 at 05:31:13PM -0400, stan wrote:
> I trimmed this thread quite a bit.
> 
> Thanks to the help I have received, I am making progress. I have looked a the
> recommended documentation, and I believe I am close. I have utilized the
> "debugging printf" capability here. Here is where I am. I have the following
> function create.
> 
> 
> DROP TRIGGER validate_task_trig ON task_instance ;
> 
> DROP FUNCTION check_permission() ;
> 
> 
> CREATE FUNCTION check_permission()
> RETURNS trigger AS $$
> DECLARE _permit boolean;
> BEGIN
>         SELECT
>                 permit INTO _permit
>         FROM
>                 permitted_work
>         WHERE
>                 NEW.employee_key = OLD.employee_key
>         AND
>                 NEW.work_type_key = OLD.work_type_key;
>         RAISE NOTICE 'New employee_id % NEW.work_type_key % _permit = %', 
>             NEW.employee_key ,
>             NEW.work_type_key ,
>             _permit ;
>         if NOT _permit THEN
>                 RAISE NOTICE 'No permission record';
>                 RAISE EXCEPTION 'No permission record';
>     ELSE
>                 RAISE NOTICE 'Found Permission Record';
>         END IF;
>         if _permit = FALSE THEN
>                 RAISE NOTICE 'Permission Denied';
>     ELSE
>                 RAISE NOTICE 'Permission Granted';
>         END IF;
> 
>         return NEW;
> END;
> $$ 
> LANGUAGE PLPGSQL;
> 
> CREATE TRIGGER validate_task_trig BEFORE INSERT OR UPDATE ON task_instance
>     FOR EACH ROW EXECUTE FUNCTION check_permission();
> 
> 
> Now the issues, currently seems to be that nothing is getting assigned to
> _permit. Here is the output of a run with 0 records in the permitted_work
> table.
> 
> NOTICE:  New employee_id 1 NEW.work_type_key 8 _permit = <NULL>
> NOTICE:  Found Permission Record
> NOTICE:  Permission Granted
> INSERT 0 1
> 
> so it appears that nothing is getting assigned to _permit. Also should I be
> checking for _permit as NOT NULL in the first if clause?
> 
> Thanks for all the had holding on this. Brand new application for me.

For the archive.

I have this working, Here is the function that I woulnd up with.


DROP TRIGGER validate_task_trig ON task_instance ;

DROP FUNCTION check_permission() ;


CREATE FUNCTION check_permission()
RETURNS trigger AS $$
DECLARE _permit boolean;
BEGIN
        SELECT
                permit INTO _permit
        FROM
                permitted_work
        WHERE
                NEW.employee_key = permitted_work.employee_key
        AND
                NEW.work_type_key = permitted_work.work_type_key;
        if _permit IS NULL THEN
                RAISE EXCEPTION 'No permission record';
    ELSE
        END IF;
        if _permit = FALSE THEN
                RAISE EXCEPTION 'Permisson Denied';
        END IF;

        return NEW;
END;
$$ 
LANGUAGE PLPGSQL;

CREATE TRIGGER validate_task_trig BEFORE INSERT OR UPDATE ON task_instance
    FOR EACH ROW EXECUTE FUNCTION check_permission();

    Thanks to all the people that were instrumental in helping me learn
    triggers and functions.


-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin