Creating References to Objects with REF

6.9 Creating References to Objects with REF

You can create views using a REF modifier to get references to objects.

Example 6-7 Query References to Objects with REF

-- Requires Ex. 6-2, Ex. 6-4, and Ex. 6-6
CREATE OR REPLACE VIEW emp_view OF emp_t WITH OBJECT IDENTIFIER(empno)
   AS SELECT e.empno, e.empname, e.salary, REF(d)
         FROM emp e, dept_view d
          WHERE e.deptno = d.deptno;

In Example 6-7, the dept_view joins the emp table on the deptno key.

The advantage of using the MAKE_REF operator, as in Example 6-6, instead of the REF modifier is that with the former, you can create circular references. For example, you can create an employee view that has a reference to the employee's department, while the department view has a list of references to the employees who work in that department.

As with synthesized objects, you can also select persistently stored references as view columns and use them seamlessly in queries. However, the object references to view objects cannot be stored persistently.