plsql - How to solve the Oracle DB trigger error? -

i wrote db trigger monitor insert action. after inserting new record, automatically set creation_date sysdate.

i error when want insert new record:

error
ora-04091: table report mutating, trigger/function may not see it
ora-06512: @ "creation_date_test", line 2
ora-04088: error during execution of trigger 'creation_date_test'

my code:

 create or replace trigger creation_date_test   after insert on report each row   begin      update report set creation_date = sysdate    rowid = :new.rowid;  end; 

i tried replace rowid = :new.rowid project_id = new.project_id. throws same error.

it sounds want before insert trigger sets :new.creation_date

create or replace trigger creation_date_test   before insert on report   each row begin   :new.creation_date := sysdate; end;