Help with constraints on object relational tables

Question

Hi
I am looking to create an object relational database with a check constraint on the relationships. For example:
* I have table called person_tab which is a table of person_t type.
* Person_t type is inherited by the manager_t type and the applicant_t type.
* I have a second table called interview_tab of interview_t type.
* The interview table has two columns (manager and appilcant) that are scope restrained to the person table.
* I would also like to put check constraints on these columns to say:
----- Manager: check the person_number is less than 20000
----- Applicant: check the person_number is greater than 19999
Can anyone tell me if this is possible and if so how can it be done?
Thanks in advance
Stephen

Answer 1

You have circular dependencies (manager_t depends upon interview_list_t depends upon interview_t depends upon manager_t) which I don't think is a good idea. But then that's probably just my old-fashioned relational head baulking at this new-fangled OO way of looking at data models. However, my experience with using types and subtypes in Oracle does teach me that this is a complete pain in the neck, because it makes changing your Type definitions a very awkward process.
am I right in saying I cannot use the check constraint?I think so. If the value range for ID is a property of being a Manager or an Applicant then properly that should be enforced by those types not by the Interview type. Then all that Interviews needs to worry about is that it gets instantiated with attributes of the correct Type.
I've simplified your model a bit. To start with I'm going to create a single PERSONS table to store both managers and applicants...
SQL> CREATE TYPE person_t AS OBJECT (
  2  personno NUMBER,
  3  surname VARCHAR2(30),
  4  forename VARCHAR2(30),
  5  dob DATE
  6  ) NOT FINAL;
  7  /
Type created.
SQL>
SQL> CREATE OR REPLACE TYPE applicant_t UNDER person_t
  2  (qualifications varchar2(200))
  3  FINAL ;
  4  /
Type created.
SQL>
SQL> CREATE OR REPLACE TYPE manager_t UNDER person_t
  2  (extension varchar2(5)) FINAL;
  3  /
Type created.
SQL>
SQL> CREATE OR REPLACE TYPE interview_t AS OBJECT (
  2  interviewno NUMBER,
  3  idate DATE,
  4  itime NUMBER,
  5  interest NUMBER,
  6  is_made_by REF manager_t,
  7  attended_by REF applicant_t
  8  ) ;
  9  /
Type created.
SQL>
SQL>
SQL> CREATE TABLE persons OF person_t
  2  /
Table created.
SQL> CREATE TABLE interviews OF interview_t
  2  /
Table created.
SQL> Okay let's create some objects...
SQL> declare
  2     mgr manager_t := manager_t(1,'RUNCITER', 'GLEN', sysdate - (42*365), 'x1234');
  3     app applicant_t := applicant_t(2,  'CHIP', 'JOE', sysdate - (38*365), 'BSc, MSc');
  4     intv interview_t;
  5     m_ref REF  person_t;
  6     a_ref REF person_t;
  7  begin
  8     INSERT INTO persons p VALUES mgr
  9         RETURNING REF(p) INTO m_ref   ;
10     INSERT INTO persons p VALUES app
11         RETURNING REF(p) INTO a_ref   ;
12     insert into interviews
13     values (interview_t(1001, sysdate, 45, 5, TREAT(m_ref AS REF manager_t)
        , TREAT(a_ref AS REF applicant_t)));
14  end;
15  /
PL/SQL procedure successfully completed.
SQL> SELECT i.interviewno, i.is_made_by.surname, i.attended_by.surname
  2  FROM interviews i
  3  /
INTERVIEWNO IS_MADE_BY.SURNAME             ATTENDED_BY.SURNAME                 
       1001 RUNCITER                       CHIP                                
SQL> Have we got integrity?
SQL> rollback
  2  /
Rollback complete.
SQL>
SQL> declare
  2     mgr manager_t := manager_t(1,'RUNCITER', 'GLEN', sysdate - (42*365), 'x1234');
  3     app applicant_t := applicant_t(2,  'CHIP', 'JOE', sysdate - (38*365), 'BSc, MSc');
  4     intv interview_t;
  5     m_ref REF  person_t;
  6     a_ref REF person_t;
  7  begin
  8     INSERT INTO persons p VALUES mgr
  9         RETURNING REF(p) INTO m_ref   ;
10     INSERT INTO persons p VALUES app
11         RETURNING REF(p) INTO a_ref   ;
12     insert into interviews
13     values (interview_t(1001, sysdate, 45, 5, TREAT(a_ref AS REF manager_t)
         , TREAT(m_ref AS REF applicant_t)));
14  end;
15  /
PL/SQL procedure successfully completed.
SQL>
SQL> SELECT i.interviewno, i.is_made_by.surname, i.attended_by.surname
  2  FROM interviews i
  3  /
INTERVIEWNO IS_MADE_BY.SURNAME             ATTENDED_BY.SURNAME                 
       1001                                                                    
SQL> Kind of, but it's not very satisfactory. Let's use separate tables for MANAGERS and APPLICANTS...
SQL> rollback
  2  /
Rollback complete.
SQL>
SQL> CREATE TABLE managers OF manager_t
  2  /
Table created.
SQL>
SQL> CREATE TABLE applicants OF applicant_t
  2  /
Table created.
SQL> declare
  2     mgr manager_t := manager_t(1,'RUNCITER', 'GLEN', sysdate - (42*365), 'x1234');
  3     app applicant_t := applicant_t(2,  'CHIP', 'JOE', sysdate - (38*365), 'BSc, MSc');
  4     intv interview_t;
  5     m_ref REF  manager_t;
  6     a_ref REF applicant_t;
  7  begin
  8     INSERT INTO managers m VALUES mgr
  9         RETURNING REF(m) INTO m_ref   ;
10     INSERT INTO applicants a VALUES app
11         RETURNING REF(a) INTO a_ref   ;
12     insert into interviews values (interview_t(1001, sysdate, 45, 5, m_ref, a_ref));
13 
14  end;
15  /
PL/SQL procedure successfully completed.
SQL>
SQL> SELECT i.interviewno, i.is_made_by.surname, i.attended_by.surname
  2  FROM interviews i
  3  /
INTERVIEWNO IS_MADE_BY.SURNAME             ATTENDED_BY.SURNAME                 
       1001 RUNCITER                       CHIP                                
SQL> rollback
  2  /
Rollback complete.
SQL> declare
  2     mgr manager_t := manager_t(1,'RUNCITER', 'GLEN', sysdate - (42*365), 'x1234');
  3     app applicant_t := applicant_t(2,  'CHIP', 'JOE', sysdate - (38*365), 'BSc, MSc');
  4     intv interview_t;
  5     m_ref REF  manager_t;
  6     a_ref REF applicant_t;
  7  begin
  8     INSERT INTO managers m VALUES mgr
  9         RETURNING REF(m) INTO m_ref   ;
10     INSERT INTO applicants a VALUES app
11         RETURNING REF(a) INTO a_ref   ;
12     insert into interviews values (interview_t(1001, sysdate, 45, 5, a_ref, m_ref));
13 
14  end;
15  /
   insert into interviews values (interview_t(1001, sysdate, 45, 5, a_ref, m_ref));
ERROR at line 12:
ORA-06550: line 12, column 69:
PL/SQL: ORA-00932: inconsistent datatypes: expected REF APC.APPLICANT_T got REF
APC.MANAGER_T
ORA-06550: line 12, column 4:
PL/SQL: SQL Statement ignored
SQL>I hope that's useful to you.
Cheers, APC
Layout of SQL*Plus session tweaked for readability
Message was edited by:
APC