1
Object Methods
Object methods, also known as subprograms, are functions or procedures that
you can declare in an object type definition to implement behavior that
you want objects of that type to perform.
Subprograms can be written in PL/SQL or virtually any other
programming language.
Methods written in PL/SQL or Java are stored in the database.
Methods written in other languages, such as C, are stored externally.
Non-comparison methods are declared as either:
1) MEMBER FUNCTION;
2) MEMBER PROCEDURE.
Comparison methods are:
1) MAP MEMBER FUNCTION;
2) ORDER MEMBER FUNCTION.
Methods have a built-in parameter named SELF that denotes the object
instance currently invoking the method. SELF can be explicitly declared, but
that is not necessary. It is simpler to write methods that reference the
attributes and methods of SELF implicitly without the SELF qualifier.
Note: SQL requires parentheses for all subprogram calls, even those that do not have arguments.
This is not true for PL/SQL.
2
Use of object methods
Table with collection
Virtual relational DB table
Object view
Method1
Method2
Method3
select …
from …
where …
Method10
Method20
Method30
3
Example. Type definition
CREATE OR REPLACE TYPE solid_typ AS OBJECT (
len INTEGER,
wth INTEGER,
hgt INTEGER,
MEMBER FUNCTION surface RETURN INTEGER,
MEMBER FUNCTION volume RETURN INTEGER,
MEMBER PROCEDURE display (SELF IN OUT NOCOPY solid_typ) );
CREATE OR REPLACE TYPE BODY solid_typ AS
MEMBER FUNCTION volume RETURN INTEGER IS
BEGIN
RETURN len * wth * hgt;
-- RETURN SELF.len * SELF.wth * SELF.hgt; -- equivalent to previous
line
END;
MEMBER FUNCTION surface RETURN INTEGER IS
BEGIN -- not necessary to include SELF in following line
RETURN 2 * (len * wth + len * hgt + wth * hgt);
END;
MEMBER PROCEDURE display (SELF IN OUT NOCOPY solid_typ) IS
BEGIN
DBMS_OUTPUT.PUT_LINE('Length: ' || len || ' - ' || 'Width: ' || wth || ' - '
|| 'Height: ' || hgt);
DBMS_OUTPUT.PUT_LINE('Volume: ' || volume || ' - ' || 'Surface area: ' ||
surface);
END;
END;
4
Table definition and queries
CREATE TABLE solids of solid_typ;
INSERT INTO solids VALUES(10, 10, 10);
INSERT INTO solids VALUES(3, 4, 5);
SELECT s.volume(), s.surface()
FROM solids s
WHERE s.len = 10;
DECLARE
solid solid_typ;
BEGIN
-- PL/SQL block for selecting a solid and displaying details
SELECT VALUE(s) INTO solid FROM solids s WHERE s.len = 10;
solid.display();
END;
SELF is always the first parameter passed to the method.
In member functions, if SELF is not declared, its parameter mode defaults
to IN.
In member procedures, if SELF is not declared, its parameter mode
defaults to IN OUT. The default behavior does not include the NOCOPY
compiler hint.
5
Methods for Comparing Objects
To compare and order variables of an object type, you must specify a basis
for comparing them. The values of a scalar data type such as CHAR or
REAL have a predefined order, which allows them to be compared. But an
object type, such as a person_typ, which can have multiple attributes of
various data types, has no predefined axis of comparison. You have the
option to define an map method or an order method for comparing objects,
but not both.
6
Map Methods
Map methods return values that can be used for comparing and sorting.
Return values can be any Oracle built-in data types (except LOBs and
BFILEs) and ANSI SQL types such as CHARACTER or REAL.
Generally, map methods perform calculations on the attributes of the object
to produce the return value.
Map methods are called automatically to evaluate such comparisons as obj_1
> obj_2 and comparisons implied by the DISTINCT, GROUP BY, UNION,
and ORDER BY clauses which require sorting by rows.
Where obj_1 and obj_2 are two object variables that can be compared using a
map method map(), the comparison:
obj_1 > obj_2
is equivalent to:
obj_1.map() > obj_2.map()
SELECT ...
MAP MEMBER
FROM ...
WHERE ...
ORDER BY ...
SELF objects
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The following example defines a map method area() that provides a
basis for comparing rectangle objects by their area:
CREATE OR REPLACE TYPE rectangle_typ AS OBJECT (
len NUMBER,
wid NUMBER,
MAP MEMBER FUNCTION area RETURN NUMBER);
CREATE OR REPLACE TYPE BODY rectangle_typ AS
MAP MEMBER FUNCTION area RETURN NUMBER IS
BEGIN
RETURN len * wid;
END area;
END;
DECLARE
po rectangle_typ;
BEGIN
po :=NEW rectangle_typ(10,5);
DBMS_OUTPUT.PUT_LINE('AREA:' || po.area()); -- prints AREA:50
END;
A subtype can declare a map method only if its root supertype declares one.
8
Order Methods
Order methods make direct one-to-one object comparisons. Unlike map
methods, they cannot determine the order of a number of objects. They
simply tell you that the current object is less than, equal to, or greater than the
object that it is being compared to, based on the criterion used.
An order method is a function for an object (SELF), with one declared
parameter that is an object of the same type. The method must return either a
negative number, zero, or a positive number. This value signifies that the
object (the implicit undeclared SELF parameter) is less than, equal to, or
greater than the declared parameter object.
As with map methods, an order method, if one is defined, is called
automatically whenever two objects of that type need to be compared.
Order methods are useful where comparison semantics may be too complex
to use a map method.
SELF objects
ORDER MEMBER
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Creating and Invoking an Order Method
CREATE OR REPLACE TYPE location_typ AS OBJECT (
building_no
NUMBER,
city
VARCHAR2(40),
ORDER MEMBER FUNCTION match (l location_typ) RETURN
INTEGER );
CREATE OR REPLACE TYPE BODY location_typ AS
ORDER MEMBER FUNCTION match (l location_typ) RETURN
INTEGER IS
BEGIN
IF building_no < l.building_no THEN
RETURN -1;
-- any negative number will do
ELSIF building_no > l.building_no THEN
RETURN 1;
-- any positive number will do
ELSE
RETURN 0;
END IF;
END;
END;
-- invoking match method
DECLARE
loc location_typ;
secloc location_typ;
a number;
BEGIN
loc :=NEW location_typ(300, 'San Francisco');
secloc :=NEW location_typ(200, 'Redwood Shores');
a := loc.match(secloc);
DBMS_OUTPUT.PUT_LINE('order (1 is greater, -1 is lesser):' ||a); -prints order:1
END;
Note: Only a type that is not derived from another type can declare an order method; a subtype cannot
define one.
10
Member methods
OSQL
MEMBER
11
Guidelines for Comparison Methods
You can declare a map method or an order method but not both. For either method type, you can
compare objects using SQL statements and PL/SQL procedural statements. However, if you do not
declare one of these methods, you can only compare objects in SQL statements, and only for equality
or inequality. Two objects of the same type are considered equal only if the values of their
corresponding attributes are equal.
When sorting or merging a large number of objects, use a map method, which maps all the objects into
scalars, then sorts the scalars. An order method is less efficient because it must be called repeatedly (it
can compare only two objects at a time).
Comparison Methods in Type Hierarchies
In a type hierarchy, if the root type (supertype) does not specify a map or an order method, neither can
the subtypes.

Map Method in a Type Hierarchy
If the root type specifies a map method, any of its subtypes can override it. If the root type does not
specify a map method, no subtype can specify one either.

Order Method in a Type Hierarchy
Only the root type can define an order method. If the root type does not define one, its subtypes cannot
add one.
Static Methods
Static methods are invoked on the object type, not its instances. You use a static method for operations
that are global to the type and do not need to reference the data of a particular object instance. A static
method has no SELF parameter.
Static methods are declared using STATIC FUNCTION or STATIC PROCEDURE.
You invoke a static method by using dot notation to qualify the method call with the name of the object
type, for example:
type_name.method()
Constructor Methods
A constructor method is a function that returns a new instance of the user-defined type and sets up the
values of its attributes. Constructor methods are either system-defined or user-defined.
To invoke a constructor, the keyword NEW can be used, but is not required.
User-Defined Constructors
You can also define constructor functions of your own to create and initialize user-defined types. The
default system-defined constructors (or attribute value constructors) are convenient to use because they
already exist, but user-defined constructors have some important advantages with respect to type
evolution.
External Implemented Methods
You can use PL/SQL to invoke external subprograms that have been written in other languages. This
provides access to the strengths and capabilities of those languages.