SQL & PL/SQL

I am familiar with the mutation error but I dont seem to be able to work this one out, if anyone could give me a hand that would be great! Thanks.

SQL> CREATE OR REPLACE PACKAGE schedule_checker IS
  2     
  3     PROCEDURE lesson_checker
  4      (fk_ins_id IN VARCHAR2,
  5       date_of IN VARCHAR2);
  6     
  7     PROCEDURE time_check
  8      (time IN NUMBER,
  9       class_she_id_vd IN VARCHAR2);
 10     END;
 11  /

Package created.

SQL>  
SQL>  CREATE OR REPLACE PACKAGE BODY schedule_checker IS
  2     PROCEDURE lesson_checker
  3      (fk_ins_id IN VARCHAR2,
  4       date_of IN VARCHAR2)
  5    IS
  6      total         number;
  7      ins_id_t     instructor.ins_id%type;
  8      date_of_t       class_schedule.date_of%type;
  9     
 10   cursor ins_count is
 11   select fk_ins_id, date_of, count(*)
 12   from class_schedule
 13   GROUP BY fk_ins_id, date_of;
 14      
 15     BEGIN
 16       
 17      
 18     open ins_count;
 19     
 20       loop
 21           fetch ins_count into ins_id_t, date_of_t, total;
 22          exit when  ins_count%NOTFOUND;
 23      
 24          if (total > 5) then  
 25                  raise_application_error(-20801,
 26           'Instructor: '  || fk_ins_id ||
 27           ' can not be assigned to more than 5 lessons on: ' || date_of_t);
 28          end if;
 29          end loop;
 30         close ins_count; 
 31     end lesson_checker; 
 32     
 33     PROCEDURE time_check
 34      (time IN NUMBER,
 35       class_she_id_vd IN VARCHAR2)
 36     IS        
 37     Begin        
 38        
 39        IF (time NOT BETWEEN 09.00 AND 22.00) THEN  
 40           raise_application_error(-20801,
 41              ' Lesson can not be scheduled outside of Gym hours! ');
 42     
 43      END IF;
 44   END time_check;
 45  END;
 46   
 47  /

Package body created.

Thats my package containing 2 procedures with constraints on the class_schedule table.

Here is my trigger to fire them,

CREATE OR REPLACE TRIGGER class_schedule_trig
BEFORE INSERT OR UPDATE ON class_schedule
FOR EACH ROW
BEGIN

IF INSERTING THEN
schedule_checker.time_check(:new.time, :new.class_she_id);
schedule_checker.lesson_checker(:new.fk_ins_id, :new.date_of);
END IF;



IF UPDATING THEN
schedule_checker.time_check(:new.time, :new.class_she_id);
schedule_checker.lesson_checker(:new.fk_ins_id, :new.date_of);
END IF;

END;
/

And here is my output when i attempt to update a table!! All inserts work fine and all triggers seem to fire correctly. I jsut get mutation problems on the updates.

SQL> UPDATE class_schedule SET time = '19.00' where class_she_id = '1';
UPDATE class_schedule SET time = '19.00' where class_she_id = '1'
       *
ERROR at line 1:
ORA-04091: table C3028390.CLASS_SCHEDULE is mutating, trigger/function may not see it
ORA-06512: at "C3028390.SCHEDULE_CHECKER", line 11
ORA-06512: at "C3028390.SCHEDULE_CHECKER", line 18
ORA-06512: at "C3028390.CLASS_SCHEDULE_TRIG", line 12
ORA-04088: error during execution of trigger 'C3028390.CLASS_SCHEDULE_TRIG'

Would i be able to solve this with a persistant package variable?

Any help is appriciated. Thanks