Chapter 33: Advanced Object-Oriented Concepts 615 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:615 ■ The object table itself is not mentioned in the query. The only table listed in the query is KEEPER. You do not need to know the name of the object table to DEREF its values. ■ The entire referenced row object was returned, not just part of the row. These are significant differences that separate object queries from relational queries. Thus, when querying your tables, you need to know the way in which their relationships are established. Are the relationships based on foreign keys and primary keys, or on object tables and REF datatypes? To help smooth the transition between relational and object-oriented approaches, Oracle allows you to create object views that contain REFs superimposed on existing relational tables. See “Object Views with REFs,” later in this chapter. The VALUE Function The DEREF function was applied to the relational table—the KEEPER table, in this case. The DEREF function returns the value of the reference that goes from the relational table to the object table. What about querying from the object table? Can you select from ANIMAL? select * from ANIMAL; BREED NAME BIRTHDATE MULE FRANCES 01-APR-02 DOG BENJI 03-SEP-01 Even though ANIMAL is an object table, you can select from it as if it were a relational table. This is consistent with the examples of inserts and selects shown earlier in this chapter. However, that is not what was shown via the DEREF. The DEREF showed the full structure of the abstract datatype used by the ANIMAL object table: select DEREF(K.AnimalKept) from KEEPER K where KeeperName = 'CATHERINE WEILZ'; DEREF(K.ANIMALKEPT)(BREED, NAME, BIRTHDATE) ANIMAL_TY('DOG', 'BENJI', '03-SEP-01') To see the same structures from a query of the ANIMAL object table, use the VALUE function. As shown in the following listing, VALUE shows you the data in the same format that DEREF will use. The parameter for the VALUE function is the table alias. select VALUE(A) from ANIMAL A where Name = 'BENJI'; P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:26 PM Color profile: Generic CMYK printer profile Composite Default screen 616 Part IV: Object-Relational Databases ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:616 VALUE(A)(BREED, NAME, BIRTHDATE) ANIMAL_TY('DOG', 'BENJI', '03-SEP-01') ANIMAL_TY('DOG', 'BENJI', '03-SEP-01') The VALUE function is useful when debugging references and within PL/SQL, as shown in “Object PL/SQL,” later in this chapter. Since it allows you to query the formatted values directly from the object table, you can select those values without using the DEREF query of KEEPER’s AnimalKept column. Invalid References You can delete the object to which a reference points. For example, you can delete a row from the ANIMAL object table to which a KEEPER record points: delete from ANIMAL where Name = 'BENJI'; The record in KEEPER that references this ANIMAL record will now have what is called a dangling REF. If you insert a new ANIMAL row for the animal named BENJI, it won’t be recognized as being part of the same reference established earlier. The reason is that the first time you inserted a BENJI row, Oracle generated an OID for the row object, and that is what the KEEPER column referenced. When you deleted the row object, the OID went away—and Oracle does not reuse OID numbers. Therefore, when the new BENJI record is entered, it is given a new OID value— and the KEEPER record still points to the old value. This is a critical difference between relational and OOP systems. In a relational system, the join between two tables is dependent only on the current data. In an OOP system, the join is between objects—and just because two objects have the same data, that doesn’t mean they are the same. Object Views with REFs You can use object views to superimpose OOP structures on existing relational tables (refer to Chapter 30). For example, you can create abstract datatypes and use them within the object view of an existing table. Using object views allows you to access the table via either relational command syntax or abstract datatype syntax. As a result, object views provide an important technological bridge from existing relational applications to object-relational applications. A Quick Review of Object Views This example from Chapter 30 will serve as part of the basis for the advanced object views in this chapter. First, a CUSTOMER table is created, with the Customer_ID column as its primary key: create table CUSTOMER (Customer_ID NUMBER constraint CUSTOMER_PK primary key, Name VARCHAR2(25), Street VARCHAR2(50), P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:27 PM Color profile: Generic CMYK printer profile Composite Default screen City VARCHAR2(25), State CHAR(2), Zip NUMBER); Next, two abstract datatypes are created. The first, ADDRESS_TY, contains attributes for addresses: Street, City, State, and Zip. The second, PERSON_TY, contains a Name attribute plus an Address attribute that uses the ADDRESS_TY datatype, as shown in the following listing: create or replace type ADDRESS_TY as object (Street VARCHAR2(50), City VARCHAR2(25), State CHAR(2), Zip NUMBER); create or replace type PERSON_TY as object (Name VARCHAR2(25), Address ADDRESS_TY); Since the CUSTOMER table was created without using the ADDRESS_TY and PERSON_TY datatypes, you need to use object views in order to access CUSTOMER data via object-based accesses (such as methods). You can create an object view that specifies the abstract datatypes that apply to the CUSTOMER table. In the following listing, the CUSTOMER_OV object view is created: create view CUSTOMER_OV (Customer_ID, Person) as select Customer_ID, PERSON_TY(Name, ADDRESS_TY(Street, City, State, Zip)) from CUSTOMER; In the creation of the CUSTOMER_OV object view, the constructor methods for the two abstract datatypes (ADDRESS_TY and PERSON_TY) are specified. You can now access the CUSTOMER table directly (as a relational table) or via the constructor methods for the abstract datatypes. The CUSTOMER table will be used in the next set of examples in this chapter. Object Views Involving References If the CUSTOMER table shown in the previous section is related to another table, you can use object views to create a reference between the tables. That is, Oracle will use the existing primary key/foreign key relationships to simulate OIDs for use by REFs between the tables. You will thus be able to access the tables either as relational tables or as objects. When you treat the tables as objects, you will be able to use the REFs to automatically perform joins of the tables (refer to “Using the DEREF Function,” earlier in this chapter, for examples). The CUSTOMER table has a primary key of Customer_ID. Let’s create a small table that will contain a foreign key reference to the Customer_ID column. In the following listing, the CUSTOMER_ CALL table is created. The primary key of the CUSTOMER_CALL table is the combination of Customer_ID and Call_Number. The Customer_ID column of CUSTOMER_CALL is a foreign Chapter 33: Advanced Object-Oriented Concepts 617 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:617 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:27 PM Color profile: Generic CMYK printer profile Composite Default screen key back to CUSTOMER—you cannot record a call for a customer who does not already have a record in CUSTOMER. A single nonkey attribute, Call_Date, is created within the CUSTOMER_ CALL table. create table CUSTOMER_CALL (Customer_ID NUMBER, Call_Number NUMBER, Call_Date DATE, constraint CUSTOMER_CALL_PK primary key (Customer_ID, Call_Number), constraint CUSTOMER_CALL_FK foreign key (Customer_ID) references CUSTOMER(Customer_ID)); For example, you could have the following CUSTOMER and CUSTOMER_CALL entries: insert into CUSTOMER values (123,'SIGMUND','47 HAFFNER RD','LEWISTON','NJ',22222); insert into CUSTOMER values (234,'EVELYN','555 HIGH ST','LOWLANDS PARK','NE',33333); insert into CUSTOMER_CALL values (123,1,TRUNC(SysDate)-1); insert into CUSTOMER_CALL values (123,2,TRUNC(SysDate)); The foreign key from CUSTOMER_CALL to CUSTOMER defines the relationship between the tables. From an OOP point of view, the records in CUSTOMER_CALL reference the records in CUSTOMER. Therefore, we must find a way to assign OID values to the records in CUSTOMER and generate references in CUSTOMER_CALL. How to Generate OIDs First, use an object view to assign OIDs to the records in CUSTOMER. Remember that OIDs are assigned to records in an object table—and an object table, in turn, is based on an abstract datatype. Therefore, we first need to create an abstract datatype that has the same structure as the CUSTOMER table: create or replace type CUSTOMER_TY as object (Customer_ID NUMBER, Name VARCHAR2(25), Street VARCHAR2(50), City VARCHAR2(25), State CHAR(2), Zip NUMBER); Now, create an object view based on the CUSTOMER_TY type, while assigning OID values to the records in CUSTOMER: create or replace view CUSTOMER_OV of CUSTOMER_TY with object identifier (Customer_ID) as 618 Part IV: Object-Relational Databases ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:618 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:27 PM Color profile: Generic CMYK printer profile Composite Default screen select Customer_ID, Name, Street, City, State, Zip from CUSTOMER; The first part of this create view command gives the view its name (CUSTOMER_OV) and tells Oracle that the view’s structure is based on the CUSTOMER_TY datatype: create or replace view CUSTOMER_OV of CUSTOMER_TY The next part of the create view command tells the database how to construct OID values for the rows in CUSTOMER. The with object identifier clause is followed by the column to use for the OID—in this case, the Customer_ID value. This will allow you to address the rows within the CUSTOMER table as if they were referenceable row objects within an object table. with object identifier (Customer_ID) as NOTE The with object identifier clause replaces the with object OID clause used in earlier versions of Oracle. The with object OID syntax is still supported for backward compatibility. The final part of the create view command gives the query on which the view’s data access will be based. The columns in the query must match the columns in the view’s base datatype. select Customer_ID, Name, Street, City, State, Zip from CUSTOMER; The rows of CUSTOMER are now accessible as row objects via the CUSTOMER_OV view. The OID values generated for the CUSTOMER_OV rows are called pkOID s, because they are based on CUSTOMER’s primary key values. Relational tables can be accessed as row objects if you create object views for them. How to Generate References The rows of CUSTOMER_CALL reference rows in CUSTOMER. From a relational perspective, the relationship is determined by the foreign key pointing from the CUSTOMER_CALL.Customer_ID column to the CUSTOMER.Customer_ID column. Now that the CUSTOMER_OV object view has been created, and the rows in CUSTOMER can be accessed via OIDs, you need to create reference values in CUSTOMER_CALL that reference CUSTOMER. Once the REFs are in place, you will be able to use the DEREF function (shown earlier in this chapter) to access the CUSTOMER data from within CUSTOMER_CALL. The create view command for the object view of CUSTOMER_CALL is shown in the following listing. It uses a new function, MAKE_REF, which is described following the listing. create view CUSTOMER_CALL_OV as select MAKE_REF(CUSTOMER_OV, Customer_ID) Customer_ID, Call_Number, Call_Date from CUSTOMER_CALL; Chapter 33: Advanced Object-Oriented Concepts 619 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:619 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:28 PM Color profile: Generic CMYK printer profile Composite Default screen 620 Part IV: Object-Relational Databases ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:620 With the exception of the MAKE_REF operation, this create view command looks like a normal create view command. The MAKE_REF operation is shown in this line: select MAKE_REF(CUSTOMER_OV, Customer_ID) Customer_ID, The MAKE_REF function takes as arguments the name of the object view being referenced and the name of the column (or columns) that form the foreign key in the local table. In this case, the Customer_ID column of the CUSTOMER_CALL table references the column that is used as the basis of OID generation in the CUSTOMER_OV object view. Therefore, two parameters are passed to MAKE_REF: CUSTOMER_OV and Customer_ID. The result of the MAKE_REF operation is given the column alias Customer_ID. Since this command creates a view, the result of an operation must be given a column alias. What does MAKE_REF do? It creates references (called pkREF s, since they are based on primary keys) from the CUSTOMER_CALL_OV view to the CUSTOMER_OV view. You can now query the two views as if CUSTOMER_OV were an object table and CUSTOMER_CALL_OV were a table that contains a REF datatype that references CUSTOMER_OV. Querying the Object Views The queries of the object views with REFs mirror the structure of the queries of table REFs. You use the DEREF function to select the value of the referenced data, as shown earlier in this chapter. Applied to the object views, the query will be select DEREF(CCOV.Customer_ID) from CUSTOMER_CALL_OV CCOV where Call_Date = TRUNC(SysDate); DEREF(CCOV.CUSTOMER_ID)(CUSTOMER_ID, NAME, STREET, CITY, STATE,ZIP) CUSTOMER_TY(123, 'SIGMUND', '47 HAFFNER RD', 'LEWISTON','NJ',22222) The query found the record in CUSTOMER_CALL for which the Call_Date value was the current system date. It then took the Customer_ID value from that record and evaluated its reference. That Customer_ID value, from the MAKE_REF function, pointed to a pkOID value in the CUSTOMER_OV object view. The CUSTOMER_OV object view returned the record whose pkOID matched the referenced value. The DEREF function then returned the value of the referenced row. The query thus returned rows from CUSTOMER even though the user only queried CUSTOMER_CALL. Object views of column objects enable you to work with tables as if they were both relational tables and object-relational tables. When extended to row objects, object views enable you to generate OID values based on established foreign key/primary key relationships. Object views allow you to continue to use the existing constraints and standard insert, update, delete, and select commands. They also allow you to use OOP features such as references against the object tables. Object views thus provide an important technological bridge for migrating to an OOP database architecture. As described earlier in this chapter, Oracle performs joins that resolve the references defined in the database. When the referenced data is retrieved, it brings back the entire row object that P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:28 PM Color profile: Generic CMYK printer profile Composite Default screen ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:621 was referenced. To reference the data, you need to establish pkOIDs in the table that is the “primary key” table in the relationship, and use MAKE_REF to generate references in the table that is the “foreign key” table in the relationship. You can then work with the data as if it were stored in object tables. Object PL/SQL PL/SQL programs can use the abstract datatypes you have created. Whereas earlier versions of PL/SQL could only use the Oracle-provided datatypes (such as DATE, NUMBER, and VARCHAR2), you can now use your own user-defined datatypes as well. The result is the merging of SQL, procedural logic, and OOP extensions—a combination referred to as object PL/SQL. The following anonymous PL/SQL block uses object PL/SQL concepts. The CUSTOMER_TY abstract datatype is used as the datatype for the Cust1 variable, and its value is populated by a query of the CUSTOMER_OV object view. set serveroutput on declare Cust1 CUSTOMER_TY; begin select VALUE(COV) into Cust1 from CUSTOMER_OV COV where Customer_ID = 123; DBMS_OUTPUT.PUT_LINE(Cust1.Name); DBMS_OUTPUT.PUT_LINE(Cust1.Street); end; The output of this PL/SQL block is SIGMUND 47 HAFFNER RD In the first part of the PL/SQL block, a variable is declared using the CUSTOMER_TY datatype: declare Cust1 CUSTOMER_TY; The Cust1 variable value is selected from the CUSTOMER_OV object view (created in the previous section of this chapter). The VALUE function is used to retrieve the data in the structure of the abstract datatype. Since the data will be selected in the format of the abstract datatype, you need to use the CUSTOMER_OV object view created on the CUSTOMER table. begin select VALUE(COV) into Cust1 from CUSTOMER_OV COV where Customer_ID = 123; Chapter 33: Advanced Object-Oriented Concepts 621 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:29 PM Color profile: Generic CMYK printer profile Composite Default screen 622 Part IV: Object-Relational Databases ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:622 The Cust1.Name and Cust1.Street values are then retrieved from the attributes of the Cust1 variable and displayed. You cannot pass the entire Cust1 variable to the PUT_LINE procedure. DBMS_OUTPUT.PUT_LINE(Cust1.Name); DBMS_OUTPUT.PUT_LINE(Cust1.Street); end; This is a deliberately simple example, but it shows the power of object PL/SQL. You can use object PL/SQL anywhere you use abstract datatypes. Your PL/SQL is thus no longer bound to the Oracle-provided datatypes, and may more accurately reflect the objects in your database. In this example, an object view was queried to illustrate that the queries can access either column objects or row objects. You can then select the attributes of the abstract datatype and manipulate or display them. If you have defined methods for the abstract datatype, you can apply them as well. For example, you can call the datatype’s constructor methods within your PL/SQL blocks. In the following example, a variable named NewCust is defined using the CUSTOMER_TY datatype. The NewCust variable is then set equal to a set of values using the CUSTOMER_TY constructor method. The NewCust variable’s set of values is then inserted via the CUSTOMER_OV object view. declare NewCust CUSTOMER_TY; begin NewCust := CUSTOMER_TY(345,'NewCust','StreetVal', 'City','ST',00000); insert into CUSTOMER_OV values (NewCust); end; You can see the result of the insert by querying CUSTOMER_OV: select Customer_ID, Name from CUSTOMER_OV; CUSTOMER_ID NAME 123 SIGMUND 234 EVELYN 345 NewCust In addition to calling constructor methods, you can call the methods you have created on your abstract datatypes. If you will be comparing the values of variables that use the abstract datatypes, you will need to define map or order methods for the datatypes. This capability allows you to further extend object PL/SQL—you define the datatypes and the functions at the database level, and they are callable within any of your PL/SQL programs. Object PL/SQL represents a significant enhancement over traditional PL/SQL. P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:29 PM Color profile: Generic CMYK printer profile Composite Default screen Objects in the Database The features available in Oracle—column objects, row objects, and object extensions to PL/SQL— enable you to implement objects in your database without sacrificing the investment you have already made in analysis and design. You can continue to create systems based on relational design techniques and tune them based on relational access methods. The tools that Oracle provides allow you to create an OOP layer above your relational tables. Once you have that layer in place, you can access the relational data as if it were stored in a fully OOP database. Having an OOP layer allows you to realize some of the benefits of an OOP system, such as abstraction and encapsulation. You can apply the methods for each abstract datatype across a set of consistently implemented objects, and benefit from object reuse and standards enforcement. At the same time, you can benefit from Oracle’s relational features. The ability to use both relational and object technology within an application lets you use the proper tool for the proper job within the database. When implementing the object portion of an object-relational database, start by defining the abstract datatypes that are the core components of your business. Every object-relational feature, whether it relates to column objects or row objects, is based on an abstract datatype. The better you have defined your datatypes and their methods, the better you will be able to implement objects. If necessary, nest objects so that you can have multiple variations of the same core datatype. The result will be a database that is properly designed to take advantage of the relational and OOP features Oracle provides now, and will provide in versions to come. Chapter 33: Advanced Object-Oriented Concepts 623 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:623 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:29 PM Color profile: Generic CMYK printer profile Composite Default screen ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 33 Blind Folio 33:624 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:14:30 PM Color profile: Generic CMYK printer profile Composite Default screen [...]... class and the name of the file must be the same In this case, the class is named AreaOfCircle, so this text is stored in a file called AreaOfCircle.java The class has two methods, called main and area When you execute the class, the main method is automatically executed The main method takes the string provided as input and parses it as an integer into the input variable: int input=Integer.parseInt(args[0]);... operations are carried out only if required; the second expression is not evaluated if the first expression determines the result In the case of the AND operator, if the first value is false, then the evaluation ends at that point and the Boolean value false is returned In the case of the OR operator, if the first expression is false, the second expression will still be evaluated because only one of the test... this chapter, you saw the basic syntax structures for Java In this section, you will see how to use that syntax to create and use objects A simple program for printing the word “Oracle” is shown in the following listing: public class HelloOracle { public static void main (String[] args) { System.out.println("Oracle"); } } This example creates a class called HelloOracle Within the HelloOracle class,... book The discussions and examples in this chapter assume you are familiar with the Java syntax and structures described in Chapter 34 This chapter does not cover every aspect of JDBC and SQLJ but focuses on the basic configuration and usage of these tools You can use JDBC to execute dynamic SQL statements in Java programs Oracle provides sample files with its standard software installation The following... datatypes listed in Table 34-1, you can use reference datatypes, which are based on the contents of variables You may note that there is no primitive datatype for variable-length character strings—Java provides a String class for that purpose Classes are discussed later in this chapter Executable Commands You can assign values to variables via the use of expressions and statements The arithmetic operators... SQLJ Programming To set your system variables, click the System icon in the Control Panel Choose the Environment tab to list the environment variables and their definitions The PATH variable should already be set, so select it and edit its value Add the new entry to the end of the list, as shown in the following listing This value should be separated from the other values in the list by a semicolon E:\Oracle\Ora91\jdbc\lib\classes12.zip... evaluates to true, then the second operand is returned, else the third is returned The syntax is as follows: expression ? operand1 : operand2 The following listing shows a sample ternary operation: aStatusVariable = (aCharVariable == 'V') ? "OK" : "Invalid"; In this example, the expression (aCharVariable == 'V') is evaluated If it is true, “OK” is returned; otherwise, “Invalid” is returned You can use the. .. the while clause If the value is less than 7, the associated statement block is executed As part of that block, the variable is incremented When the block completes, the variable is again evaluated and the loop continues NOTE For examples of WHILE loop processing, see “Classes” later in this chapter You could also write this as a DO-WHILE loop: int aNumberVariable = 3; do { some_processing_statement aNumberVariable++;... executed; otherwise, flow will continue to the next part of the program The following is the general syntax for if clauses: if (expression) { statement } Notice the lack of a then clause If the expression being evaluated is true, the following block is automatically executed You can also have else clauses to evaluate different conditions, as shown in the following listing: if (expression) { statement } else... that class, the example issues the following commands: Statement stmt conn.createStatement(); ResultSet rset = stmt.executeQuery ("select ENAME from EMP"); //iterate through the result set and print the employee names while (rset.next ()) System.out.println (rset.getString (1)); This example assumes that a connection to the database has already been established The first line of the example creates a variable . provides a String class for that purpose. Classes are discussed later in this chapter. Executable Commands You can assign values to variables via the use of expressions and statements. The arithmetic operators. it as if it were a relational table. This is consistent with the examples of inserts and selects shown earlier in this chapter. However, that is not what was shown via the DEREF. The DEREF showed. using the CUSTOMER_TY datatype. The NewCust variable is then set equal to a set of values using the CUSTOMER_TY constructor method. The NewCust variable s set of values is then inserted via the