Triggers are gone when updates the view they are on?

Question

I found that when I updated a view, all the triggers on this view were dropped.
Is this supposed to be or I did something wrong?

Answer 1

To answer the second part of your question, triggers on tables are not dropped if you modify the tables, unlike when you modify views. However, if you modify the table in such a way that it invalidates the trigger, the trigger becomes invalid, but not dropped. Please see the example below.
scott@ORA92> create table test_tab
  2    (col1 number)
  3  /
Table created.
scott@ORA92> create sequence test_seq
  2  /
Sequence created.
scott@ORA92> create or replace trigger test_trig
  2    before insert on test_tab
  3    for each row
  4  begin
  5    select test_seq.nextval into :new.col1 from dual;
  6  end test_trig;
  7  /
Trigger created.
scott@ORA92> show errors
No errors.
scott@ORA92> insert into test_tab values (null)
  2  /
1 row created.
scott@ORA92> select * from test_tab
  2  /
      COL1
         1
scott@ORA92> commit
  2  /
Commit complete.
scott@ORA92> alter table test_tab add col2 number
  2  /
Table altered.
scott@ORA92> insert into test_tab (col2) values (10)
  2  /
1 row created.
scott@ORA92> select * from test_tab
  2  /
      COL1       COL2
         1
         2         10
scott@ORA92> commit
  2  /
Commit complete.
scott@ORA92> select status from user_triggers where trigger_name = 'TEST_TRIG'
  2  /
STATUS
ENABLED
scott@ORA92> select status from user_objects where object_name = 'TEST_TRIG'
  2  /
STATUS
VALID
scott@ORA92> alter table test_tab drop column col1
  2  /
Table altered.
scott@ORA92> select status from user_triggers where trigger_name = 'TEST_TRIG'
  2  /
STATUS
ENABLED
scott@ORA92> select status from user_objects where object_name = 'TEST_TRIG'
  2  /
STATUS
INVALID
scott@ORA92> insert into test_tab (col2) values (20)
  2  /
insert into test_tab (col2) values (20)
ERROR at line 1:
ORA-04098: trigger 'SCOTT.TEST_TRIG' is invalid and failed re-validation
scott@ORA92> select * from test_tab
  2  /
      COL2
        10