Using operator deref - manipulating objects in pl sql, PL-SQL Programming

Using Operator DEREF:

You cannot navigate through refs within the PL/SQL procedural statements. Rather than, you should use the operator DEREF in the SQL statement. The DEREF take as its argument that reference to an object, and then returns the value of that object. If the ref is dangling, the DEREF returns a null object.

In the illustration below, you dereference the ref to a Person object. Note that you select the ref from dummy table dual. You do not require specifying an object table and search criteria as each object stored in an object table has an immutable, exclusive object identifier that is a part of every ref to that object.

DECLARE

p1 Person;

p_ref REF Person;

name VARCHAR2(15);

BEGIN

...

/* Suppose that p_ref holds a valid reference

to an object stored in an object table. */

SELECT DEREF(p_ref) INTO p1 FROM dual;

name := p1.last_name;

You can use DEREF in successive SQL statements to dereference refs, as the

following example shows:

CREATE TYPE PersonRef AS OBJECT (p_ref REF Person)

/

DECLARE

name VARCHAR2(15);

pr_ref REF PersonRef;

pr PersonRef;

p Person;

BEGIN

...

/* Assume pr_ref holds a valid reference. */

SELECT DEREF(pr_ref) INTO pr FROM dual;

SELECT DEREF(pr.p_ref) INTO p FROM dual;

name := p.last_name;

...

END

/

The later illustration shows that you cannot use the operator DEREF within procedural statements:

BEGIN

...

p1 := DEREF(p_ref); -- illegal

Within the SQL statements, you can use the dot notation to navigate throughout the object columns to ref attributes and through one ref attribute to the other. You can also navigate through the ref columns to attributes if you use a table alias. For illustration, the syntax below is valid:

table_alias.object_column.ref_attribute

table_alias.object_column.ref_attribute.attribute

table_alias.ref_column.attribute

Suppose that you have to run the SQL*Plus script below that creates object types Address and Person and object table persons:

CREATE TYPE Address AS OBJECT (

street VARCHAR2(35),

city VARCHAR2(15),

state CHAR(2),

zip_code INTEGER)

/

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

/

The Ref attribute home_address corresponds to a column in the object table persons that holds refs to the Address objects stored in some another table. After populating the tables, you can select a particular address by de-referencing its ref, as shown:

DECLARE

addr1 Address,

addr2 Address,

...

BEGIN

SELECT DEREF(home_address) INTO addr1 FROM persons p

WHERE p.last_name = 'Derringer';

In the illustration below, you navigate through ref column home_address to attribute the street. In this situation, the table alias is needed.

DECLARE

my_street VARCHAR2(25),

...

BEGIN

SELECT p.home_address.street INTO my_street FROM persons p

WHERE p.last_name = 'Lucas';

Posted Date: 10/6/2012 8:22:34 AM | Location : United States







Related Discussions:- Using operator deref - manipulating objects in pl sql, Assignment Help, Ask Question on Using operator deref - manipulating objects in pl sql, Get Answer, Expert's Help, Using operator deref - manipulating objects in pl sql Discussions

Write discussion on Using operator deref - manipulating objects in pl sql
Your posts are moderated
Related Questions
Example of Table Literal - SQL Example: A Table Literal (correct version) VALUES ('S1', 'C1', 'Anne'), ('S1', 'C2', 'Anne'), ('S2', 'C1', 'Boris'), ('S3', 'C3'

Creating a Table Syantax: CREATE TABLE ENROLMENT (StudentId SID, Name   VARCHAR (30) NOT NULL, CourseId CID, PRIMARY KEY (StudentId, CourseId)) ; Explan

Use the RETURNING Clause Frequently, the application requires information about the row affected by a SQL operation, for illustration, to produce a report or take a subsequent

Assigning and Comparing Collections One collection can be assigned to other by an SELECT, INSERT, UPDATE, or FETCH statement, an assignment statement, or by a subprogram call. A

UPDATE Command- SQL Loosely speaking, UPDATE changes some of the column values of some existing rows of its target table. Thus, although some rows disappear from the target an

Explicitly specifying the join condition - SQL SELECT * FROM IS_CALLED JOIN IS_ENROLLED_ON ON ( IS_CALLED.StudentId = IS_ENROLLED_ON.StudentId ) Now, the key word JO

1- You can check attribute names from each table in DBF11 by running for example:  desc dbf11.Member;  desc dbf11.Agent;  desc dbf11.Producer; Because some attribute names in

"Not Enforced" Table Constraints A constraint that is not enforced is not really a constraint within the meaning of the act, but SQL does have such a concept and it needs to b

Use Bulk Binds If SQL statements execute inside a loop using the collection elements as bind variables, context switching between the PL/SQL & SQL engines can slow down the ex

%FOUND Until the SQL data manipulation statement is executed, the %FOUND yields NULL. Afterward, the %FOUND yields TRUE, when an INSERT, UPDATE, or DELETE statement affected o