OBJECT VIEWS AND METHODS

OBJECT VIEWS

If you want to implement objects with the existing table, object views come into picture.

You define the object and create a view which relates this object to the existing table nothing but object view.

Object views are used to relate the user defined objects to the existing table.

Ex:

     1) Assume that the table student has already been created with the following columns

          SQL> create table student(no number(2),name varchar(10),hno number(3),city

                  varchar(10));

     2) Create the following types

          SQL> create type addr as object(hno number(2),city varchar(10));/

          SQL> create type stud as object(name varchar(10),address addr);/

     3) Relate the objects to the student table by creating the object view

          SQL> create view student_ov(no,stud_info) as select no,stud(name,addr(hno,city)) from

                  student;

     4) Now you can insert data into student table in two ways

          a) By regular insert

               SQL> Insert into student values(1,’sudha’,111,’hyd’);

          b) By using object view

               SQL> Insert into student_ov values(1,stud(‘sudha’,addr(111,’hyd’)));

METHODS

You can define methods which are nothing but functions in types and apply in the tables which holds the types;

Ex:

    1) Defining methods in types

         SQL> Create type stud as object(name varchar(10),marks number(3),

                 Member function makrs_f(marks in number) return number,

                   Pragma restrict_references(marks_f,wnds,rnds,wnps,fnps));/

     2) Defining type body

          SQL> Create type body stud as

                  Member function marks_f(marks in number) return number is

                  Begin

                     Return (marks+100);

                  End marks_f;

                  End;/

      3) Create a table using stud type

           SQL> Create table student(no number(2),info stud);

      4) Insert some data into student table

           SQL> Insert into student values(1,stud(‘sudha’,100));

      5) Using method in select

           SQL> Select s.info.marks_f(s.info.marks) from student s;

      -- Here we are using the pragma restrict_references to avoid the writes to the database.