Manipulating Objects through SQL

Assume that you have run the following SQL*Plus script, which creates object types

Address and Person and object table persons:

/

CREATE TYPE Person AS OBJECT ( first_name VARCHAR2(15), last_name VARCHAR2(15), birthday DATE,

home_address REF Address, -- shared with other Person objects phone_number VARCHAR2(15))

/

CREATE TABLE persons OF Person

/

Ref attribute home_address corresponds to a column in object table persons that holds refs to Address objects stored in some other table. After populating the tables, you can select a particular address by dereferencing its ref:

DECLARE

addr1 Address, addr2 Address,

BEGIN

SELECT DEREF(home_address) INTO addr1 FROM persons p WHERE p.last_name = 'Derringer';

In the example below, you navigate through ref column home_address to attribute street. In this case, a table alias is required.

DECLARE

my_street VARCHAR2(25), BEGIN

SELECT p.home_address.street INTO my_street FROM persons p WHERE p.last_name = 'Lucas';

Inserting Objects

You use the INSERT statement to add objects to an object table. In the following example, you insert a Person object into object table persons:

BEGIN

INSERT INTO persons

VALUES ('Jenifer', 'Lapidus', ...);

Alternatively, you can use the constructor for object type Person to insert an object into object table persons:

BEGIN

INSERT INTO persons

VALUES (Person('Albert', 'Brooker', ...));

In the next example, you use the RETURNING clause to store Person refs in local variables. Notice how the clause mimics a SELECT statement.You can also use the RETURNING clause in UPDATE and DELETE statements.

DECLARE

p1_ref REF Person;

Using PL/SQL Object Types 12-21

Manipulating Objects through SQL

p2_ref REF Person; BEGIN

INSERT INTO persons p

VALUES (Person('Paul', 'Chang', ...)) RETURNING REF(p) INTO p1_ref;

INSERT INTO persons p

VALUES (Person('Ana', 'Thorne', ...)) RETURNING REF(p) INTO p2_ref;

To insert objects into an object table, you can use a subquery that returns objects of the same type. An example follows:

BEGIN

INSERT INTO persons2

SELECT VALUE(p) FROM persons p

WHERE p.last_name LIKE '%Jones';

The rows copied to object table persons2 are given new object identifiers. No object identifiers are copied from object table persons.

The script below creates a relational table named department, which has a column of type Person, then inserts a row into the table. Notice how constructor Person() provides a value for column manager.

CREATE TABLE department ( dept_name VARCHAR2(20), manager Person, location VARCHAR2(20))

/

INSERT INTO department

VALUES ('Payroll', Person('Alan', 'Tsai', ...), 'Los Angeles')

/

The new Person object stored in column manager cannot be referenced because it is stored in a column (not a row) and therefore has no object identifier.

Updating Objects

To modify the attributes of objects in an object table, you use the UPDATE statement, as the following example shows:

Deleting Objects

You use the DELETE statement to remove objects (rows) from an object table. To remove objects selectively, use the WHERE clause:

BEGIN

DELETE FROM persons p

WHERE p.home_address = '108 Palm Dr';

END;

12-22 PL/SQL User's Guide and Reference