Referential integrity based on a view

Question

Hi,
I am having difficulty in trying to build referential integrity based on a view.
     I have explained below with an example:
     I have a table called 'vehicles' which is the master table.
     CREATE TABLE vehicles(
     type VARCHAR2(20),
     model_number NUMBER(5),
     price NUMBER(5),
     CONSTRAINT vehicles_pk PRIMARY KEY(type, model_number)
     INSERT INTO vehicles(type, model_number, price) VALUES ('CAR', 1, 100);
     INSERT INTO vehicles(type, model_number, price) VALUES ('BIKE', 1, 50);
     INSERT INTO vehicles(type, model_number, price) VALUES ('CAR', 5, 200);
     INSERT INTO vehicles(type, model_number, price) VALUES ('BIKE', 7, 50);
     I have a view called 'vu_cars' which lists only the CAR from the table 'vehicles'.
     CREATE VIEW vu_cars
     AS
     SELECT model_number
     FROM vehicles
     WHERE
          type = 'CAR';
     I have a table called 'car_properties' which contains the car properties and has referential integrity based on the view 'vu_cars'
-- This create statement throws an error, am I missing something ... ?
     CREATE TABLE car_properties(
     model_number VARCHAR2(20),
     number_of_doors NUMBER(5),
     PRIMARY KEY(model_number),
     CONSTRAINT vu_cars_fk FOREIGN KEY (model_number) REFERENCES vu_cars(model_number)
-- Actually I wanted to execute the below insert statements, but am stuck with the above create statement of the table car_properties. Is there anyway to resolve this ?
     --Below should be inserted correctly:
     INSERT INTO car_properties(model_number, number_of_doors) VALUES (1, 4);
     INSERT INTO car_properties(model_number, number_of_doors) VALUES (5, 2);
     --This should throw an error:
     INSERT INTO car_properties(model_number, number_of_doors) VALUES (7, 2);

Answer 1

One approach would be to:
1. Add a TYPE column to CAR_PROPERTIES.
2. Add a check constraint on the TYPE column in CAR_PROPERTIES that requires it to equal 'CAR'.
3. Create a foreign key constraint on CAR_PROPERTIES referencing both MODEL_NUMBER and TYPE in VEHICLES. This requires a primary or unique constraint on these two columns in VEHICLES, but you already have one. However, both columns should have the same data type in both tables.
It might look something like this:
SQL> CREATE TABLE vehicles(
  2  type VARCHAR2(20),
  3  model_number NUMBER(5),
  4  price NUMBER(5),
  5  CONSTRAINT vehicles_pk PRIMARY KEY(type, model_number)
  6  );
Table created.
SQL> INSERT INTO vehicles(type, model_number, price) VALUES ('CAR', 1, 100);
1 row created.
SQL> INSERT INTO vehicles(type, model_number, price) VALUES ('BIKE', 1, 50);
1 row created.
SQL> INSERT INTO vehicles(type, model_number, price) VALUES ('CAR', 5, 200);
1 row created.
SQL> INSERT INTO vehicles(type, model_number, price) VALUES ('BIKE', 7, 50);
1 row created.
SQL> CREATE TABLE car_properties(
  2  -- Note new column with both not null and check constraint
  3  type VARCHAR2(20) not null check (type = 'CAR'),
  4  -- Note change in data type to be the same as vehicles table
  5  model_number NUMBER(5) not null,
  6  number_of_doors NUMBER(5),
  7  PRIMARY KEY(model_number),
  8  -- Note new constraint referencing vehicles table
  9  CONSTRAINT vehicles_fk FOREIGN KEY (type, model_number) REFERENCES vehicles(type, model_number)
10  );
Table created.
SQL> INSERT INTO car_properties(type, model_number, number_of_doors) VALUES ('CAR', 1, 4);
1 row created.
SQL> INSERT INTO car_properties(type, model_number, number_of_doors) VALUES ('CAR', 5, 2);
1 row created.
SQL> INSERT INTO car_properties(type, model_number, number_of_doors) VALUES ('BIKE', 7, 2);
INSERT INTO car_properties(type, model_number, number_of_doors) VALUES ('BIKE', 7, 2)
ERROR at line 1:
ORA-02290: check constraint (TEMP.SYS_C0095831) violated
SQL> INSERT INTO car_properties(type, model_number, number_of_doors) VALUES ('CAR', 7, 2);
INSERT INTO car_properties(type, model_number, number_of_doors) VALUES ('CAR', 7, 2)
ERROR at line 1:
ORA-02291: integrity constraint (TEMP.VEHICLES_FK) violated - parent key not
found
SQL> INSERT INTO car_properties(type, model_number, number_of_doors) VALUES (NULL, 1, 4);
INSERT INTO car_properties(type, model_number, number_of_doors) VALUES (NULL, 1, 4)
ERROR at line 1:
ORA-01400: cannot insert NULL into ("TEMP"."CAR_PROPERTIES"."TYPE")Defining a default value for the TYPE column in CAR_PROPERTIES (to set it to 'CAR') might make this approach a little less obtrusive.