Errors when inserting and updating form using VIEW.

Question

Here's my view:
CREATE OR REPLACE FORCE
VIEW  "SH_ADD_EMPLOYEES_VW" ("EMP_ID", "DEPT_ID", "JOB_DESC_ID", "EMPNO", "EMP_FIRST", "EMP_LAST", "USER_NAME", "USER_INI", "DEPTNO", "DEPT_DESC", "ROLES_ID", "ADMIN", "CREATES", "APPROVES", "QUALITY", "CUST_SVC", "SH_LOCAL",
"SH_OFFICE", "SYSTEM")
AS
  select
"SH_EMPLOYEES"."EMP_ID" as "EMP_ID",
"SH_EMPLOYEES"."DEPT_ID" as "DEPT_ID",
"SH_EMPLOYEES"."JOB_DESC_ID" as "JOB_DESC_ID",
"SH_EMPLOYEES"."EMPNO"  as "EMPNO",
"SH_EMPLOYEES"."EMP_FIRST" as "EMP_FIRST",
"SH_EMPLOYEES"."EMP_LAST" as "EMP_LAST",
"SH_EMPLOYEES"."USER_NAME" as "USER_NAME",
"SH_EMPLOYEES"."USER_INI" as "USER_INI",
"SH_EMPLOYEES"."DEPTNO" as "DEPTNO",
"SH_EMPLOYEES"."DEPT_DESC" as "DEPT_DESC",
"DOC_ROLES"."ROLES_ID" as "ROLES_ID",
"DOC_ROLES"."ADMIN" as "ADMIN",
"DOC_ROLES"."CREATES" as "CREATES",
"DOC_ROLES"."APPROVES" as "APPROVES",
"DOC_ROLES"."QUALITY" as "QUALITY",
"DOC_ROLES"."CUST_SVC" as "CUST_SVC",
"DOC_ROLES"."SH_LOCAL" as "SH_LOCAL",
"DOC_ROLES"."SH_OFFICE" as "SH_OFFICE",
"DOC_ROLES"."SYSTEM" as "SYSTEM"
FROM "SH_EMPLOYEES" "SH_EMPLOYEES", "DOC_ROLES" "DOC_ROLES"
where "SH_EMPLOYEES"."EMP_ID" = "DOC_ROLES"."EMP_ID"
Here's my trigger (note - I am not using the EXCEPTION clause or (declaration of it)  because it throws an error on msg=>: 'This is my message.' Any help here would be great as well.)
CREATE OR REPLACE TRIGGER bi_ADD_EMPLOYEES_VW
INSTEAD OF insert ON SH_ADD_EMPLOYEES_vw
for each row
declare
duplicate_info EXCEPTION;
PRAGMA EXCEPTION_INIT(duplicate_info, -00001);
begin
insert into SH_EMPLOYEES
(EMP_ID, DEPT_ID, JOB_DESC_ID, EMPNO, EMP_FIRST, EMP_LAST, USER_NAME, USER_INI, DEPTNO, DEPT_DESC)
values
(:new.EMP_ID, :new.DEPT_ID, :new.JOB_DESC_ID, :new.EMPNO, :new.EMP_FIRST, :new.EMP_LAST, :new.USER_NAME, :new.USER_INI, :new.DEPTNO, :new.DEPT_DESC);
insert into DOC_ROLES
(ROLES_ID, ADMIN, CREATES, APPROVES, QUALITY, CUST_SVC, SH_LOCAL, SH_OFFICE, SYSTEM)
VALUES (
:new.ROLES_ID, :new.ADMIN, :new.CREATES, :new.APPROVES, :new.QUALITY, :new.CUST_SVC, :new.SH_LOCAL, :new.SH_OFFICE, :new.SYSTEM);
EXCEPTION
WHEN duplicate_info THEN
  RAISE_APPLICATION_ERROR (
   num=> -20107
   msg=> 'Duplicate employee');
END bi_ADD_EMPLOYEES_VW;
ERROR ON UPDATE:
ORA-20505: Error in DML: p_rowid=1001,
p_alt_rowid=EMP_ID, p_rowid2=2, p_alt_rowid2=ROLES_ID. ORA-01779: cannot modify
a column which maps to a non key-preserved table
ERROR ON INSERT:
ORA-01400: cannot insert NULL into
("SPICE_HUNTER1"."SH_EMPLOYEES"."EMP_ID") ORA-06512: at
"SPICE_HUNTER1.BI_SH_ADD_EMPLOYEES_VW", line 3 ORA-04088: error during execution
of trigger 'SPICE_HUNTER1.BI_SH_ADD_EMPLOYEES_VW' ORA-06512: at
"SYS.WWV_DBMS_SQL", line 549 ORA-06512: at "APEX_040000.WWV_FLOW_DML", line 1121
ORA-22816: unsupported feature with RETURNING clause
Error Unable to process row on table SH_ADD_EMPLOYEES_VW

Answer 1

From what I see you are not handling emp_id when it is null.. you need to assign it a value when null from sequence.. that column cannot be null, hence the error, and in order to "modify" a column in that table the DML needs that id to have a value.