DEV-6: Advanced Object-Oriented Programming in the ABL Evan Bleicher [email protected] Senior...

DEV-6: Advanced Object-Oriented Programming in the ABL

Evan [email protected] Development Manager

Shelley [email protected]

Architect

© 2006 Progress Software Corporation2DEV-6 Advanced Object-oriented Programming in the ABL

D I S C L A I M E R

Under Development

This talk includes information about potential future products and/or product enhancements.

What we are going to say reflects our current thinking, but the information contained herein is preliminary and subject to change. Any future products we ultimately deliver may be materially different from what is described here.

D I S C L A I M E R


Agenda

Order Entry System Object Model Abstract Programming with Classes Working with Datasets / Temp-tables in Classes Miscellaneous Topics:

• Debugging with Classes• Using SUPER in Classes • Accessing Classes on the AppServer• Error Handling policy for Classes• Proper Encapsulation in Classes• Compiler Tips and Tricks• Coding Standards


Order Entry System Object Model

“Business Entity”Interface between

DA layer and Presentation /

Integration

“Data Access Object”

Interface to Data Store

Use OpenEdge® Reference Architecture

PresentationPresentation

Business ServicesBusiness Services

Data AccessData Access

Data SourcesData Sources

Co

mm

on

Infrastru

cture

Co

mm

on

Infrastru

cture

Enterprise ServicesEnterprise Services


Order Entry Object Model - Handout

Inherits

CLASS Acme.BusinessEntity

DEF VAR rDataObject AS CLASS IDataAccess

METHOD VOID fetchWhere ( )

METHOD VOID saveChanges ( )

CLASS Acme.BEOrder INHERITS Acme.BusinessEntity

METHOD VOID processOrder ( )

…

Inherits

CLASS Acme.BEInternalOrder INHERITS Acme.BEOrder

DEF VAR invoiceNum AS INT

METHOD VOID OVERRIDE processOrder ( )…

CLASS Acme.BEExternalOrder INHERITS Acme.BEOrder

DEF VAR crossDept AS INT

METHOD VOID OVERRIDE processOrder ( )…

Inherits

CLASS Acme.DAOrderSuper

PROTECTED TEMP-TABLE ttOlinePROTECTED TEMP-TABLE ttOrderPROTECTED DATASET dsOrder…

INTERFACE Acme.IDataAccess

METHOD LONGCHAR selectRecords (…)

ImplementsCLASS Acme.DAItem IMPLEMENTS Acme.IDataAccess, Acme.IList

…

CLASS Acme.DAOrderINHERITS Acme.DAOrderSuper IMPLEMENTS Acme.IDataAccess, Acme.IList

METHOD LONGCHAR selectRecords (…)METHOD NextRecord ( )METHOD PrevRecord ( )

METHOD VOID postOlineFill (…)

METHOD VOID postDSFill (…)

Implements

INTERFACE Acme.IList

METHOD nextRecord ( )

METHOD prevRecord ( )…


Order Entry Object Model – Data Access Layer

CLASS CLASS Acme.DAOrderSuperAcme.DAOrderSuper

CLASS CLASS Acme.DAItemAcme.DAItem

INTERFACE INTERFACE Acme.IListAcme.IList

ImplementsCLASS CLASS

Acme.DAOrderAcme.DAOrder

Inherits

INTERFACE INTERFACE Acme.IDataAccessAcme.IDataAccess

Implements

Data Access Interface

Navigation Interface

Super Order Class

Specific Order Class

Specific Item Class

PROTECTED TEMP-TABLE ttOlinePROTECTED TEMP-TABLE ttOrderPROTECTED DATASET dsOrder




Implements


Order Entry Object Model – Business Servicing Layer

CLASS CLASS Acme.BusinessEntityAcme.BusinessEntity

CLASS CLASS Acme.BEOrderAcme.BEOrder

CLASS CLASS Acme.BEInternalOrderAcme.BEInternalOrder

CLASS CLASS Acme.BEExternalOrderAcme.BEExternalOrder

Inherits

Inherits Inherits

Business Entity Class

Order Class

Specific Internal Order Class

Specific External Order Class

DEF VAR rDataObject AS CLASS Acme.IDataAccess

METHOD VOID fetchWhere ( )METHOD VOID saveChanges ( )

METHOD VOID processOrder( )

METHOD OVERRIDE VOID processOrder ( )



Physical Architecture of A Class Hierarchy

COMPILE Acme/BEExternalOrder.cls SAVE.

Inherits

Inherits

<propath> / Acme / <propath> / Acme / BusinessEntity.clsBusinessEntity.cls

<propath> / Acme /<propath> / Acme / BEOrder.clsBEOrder.cls

<propath> / Acme /<propath> / Acme / BEExternalOrder.clsBEExternalOrder.cls


COMPILE

COMPILE

COMPILE



Inherits

Inherits

<propath> / Acme / <propath> / Acme / BusinessEntity.clsBusinessEntity.cls






Inherits

Inherits

Digest: <val>

Inherits:<class-type, digest-val>

Implements:<class-type, digest-val><class-type, digest-val>…

Class r-code Data<propath> / Acme / <propath> / Acme / BusinessEntity.clsBusinessEntity.cls



<propath> / Acme / BEOrder.r

5678Acme/BusinessEntity, 1234None

<propath> / Acme / BusinessEntity.r

1234NoneNone

<propath> / Acme / BEExternalOrder.r

9000Acme/BEOrder, 5678None


Agenda




Abstract (Generic) Programming

Define super class / interface for abstraction• Define abstract methods

Use abstract object• Define object reference for super class / interface• Set object ref to NEW subclass object• Polymorphism causes method calls on object ref to

run method in subclass

Abstract code should be put in top most class• Supports abstraction and reuse


Choosing between Super Classes and Interfaces

“Both”• Define API (contract) for abstract programming• Support polymorphism

Super class• Contain common code for sharing / augmenting• Contain protected data members

Interfaces• Use when no common behavior exists• Use to emulate multiple inheritance


Abstract Programming Using Interfaces

Define an interface• Common methods put in interface

• Implementer must provide code for methods


CLASS CLASS Acme.DAOrderAcme.DAOrder

CLASS CLASS Acme.DAItemAcme.DAItem

Implements




Interface

Implementer Implementer


Abstract Programming Using Super Classes

Define a super class• Common methods including code put in super class

• Optionally, subclass can override common code

CLASS CLASS Acme.BEOrderAcme.BEOrder

CLASS CLASS Acme.BEInternalOrderAcme.BEInternalOrder

CLASS CLASS Acme.BEExternalOrderAcme.BEExternalOrder



METHOD VOID processOrder ( )

Super Class

Subclass Subclass


Abstract Programming Sample

CLASS Acme.BusinessEntity: /* Define variable for interface type */ DEFINE PROTECTED VARIABLE rDataObject

AS CLASS Acme.IDataAccess NO-UNDO.

/* Generic method – works on any class that implements Acme.IDataAccess */ METHOD PUBLIC LONGCHAR fetchWhere (…): lcVar1 = rDataObject:selectRecords (…).…

CLASS Acme.BEOrder: CONSTRUCTOR BEOrder ( ): /* Create Order data object assign to super class reference*/ rDataObject = NEW Acme.DAOrder ( ). lcVar2 = rDataObject:fetchWhere (…).…


Demo of Abstract Programming


Multiple Inheritance Using Interfaces

Some older OO languages support multiple inheritance

Newer OO languages support multiple APIs using interfaces – class inheritance is single



INTERFACE INTERFACE Acme.IListAcme.IList

Implements


METHOD NextRecord ( )

METHOD PrevRecord ( )


METHOD NextRecord ( )

METHOD PrevRecord ( )


Agenda




Datasets and Temp-Tables in Classes

Defined in a class as either PROTECTED or PRIVATE – class data member

Passed as parameters to methods (like procs)

Cannot be returned from a method (like UDFs)

Temp-table columns can contain Progress.Lang.Object • Automatically upcast when put into column

• CAST column value to subclass before use


Using a Class from a Temp-Table Column

Use TYPE-OF function with CAST

DEFINE VAR rOrder AS Acme.BEOrder.

FOR EACH myTT:

/* See if column is an external order */ IF TYPE-OF (myTT.rObj, Acme.BEExternalOrder) THEN

rOrder = CAST (myTT.rObj, Acme.BEExternalOrder).

/* See if column is an internal order */

ELSE IF TYPE-OF (myTT.rObj, Acme.BEInternalOrder) THEN

rOrder = CAST (myTT.rObj, Acme.BEInternalOrder).

END.


Protected DataSets / Temp-Tables

PROTECTED access in subclass “automatic” – use normal syntax • Better than passing BY-REFERENCE or BIND,

defining as SHARED

• No need to include definition in subclass

CLASS CLASS Acme.DAOrderSuperAcme.DAOrderSuper


Inherits

PROTECTED TEMP-TABLE ttOlinePROTECTED TEMP-TABLE ttOrderPROTECTED DATASET dsOrder

FOR EACH ttOrder:

DISPLAY ttOrder.CustomerName


ProDataSet Event Handlers

Callbacks can be methods as well as internal procedures

Protected datasets can have handlers in subclass

CLASS CLASS Acme. Acme.

DAOrderSuperDAOrderSuper


Inherits

/* Set callback in subclass for dataset in super class */

hDSOrder = dsOrder:HANDLE.

hDSOrder:SET-CALLBACK (“AFTER-FILL”, “postDSFill”).…

METHOD VOID postDSFill (DATASET dsOrder).…


Demo of Datasets and Temp-Tables


Agenda




Debugging Classes

Debugger works with Classes Demos have been running classes in the

debugger• Steps into each constructor / destructor in

hierarchy• Shows polymorphism in action – subclass

method is stepped into Remember

• Open class file in debugger to see data members


Using SUPER in Classes

Use SUPER ( ) to call super class constructor• Only valid in constructor

• Must be first line if present

Use SUPER:method-name ( ) to call a method higher in the class hierarchy• Valid in constructor, destructor, methods

• Must specify method-name (unlike procedures)


AppServer

Running with Classes on an AppServer

Option 1: Classes on both client and server– Provide serialize and deserialize methods– Remote class access support coming

Option 2: Dispatch procedure on AppServer– Client interacts with dispatcher– Data passed in temp-table or dataset

Remote classes cannot be accessed from client

Client AppServerDataData

Client

Data

Dispatch.pRUN dispatch.p SET h.RUN getData (myTT) in h. Dataset /

Temp-tableData

DataDataData

Data

Data

Dataset / Temp-table

DataDataset /

Temp-table


Error Handling

RETURN ERROR not allowed in classes

Options:1. Use output parameter or return type

2. Use STOP mechanism

Improved error handling coming!


Options for Handling Errors in Constructor

1. Constructor handles error– Run DELETE THIS-OBJECT in constructor

Automatically runs destructors for any successful constructors in hierarchy

– Caller checks object reference for unknown

3. Use an output parameter to indicate error to caller– Caller must check for error and delete object

2. Compile/Deployment errors found during NEW– Mismatched parameters, super class not found– Automatically aborts new and cleans up– Caller checks object reference for unknown or

ERROR-STATUS:ERROR


Demo of Error Handling in Classes


Encapsulation

Good practice to keep data members protected or private

Provide “getter” and “setter” routines to access data members• Safe access

• Support read-only or write-only

PROPERTY class members coming!


Compiling Tips and Techniques

Strong-typing only works if you compile – running “compile-on-the-fly” catches all errors at runtime• Be safe – always rebuild/compile your code

Recompiling only super classes can result in runtime errors – always recompile subclasses that depend on super classes to be safe• Exceptions to this rule…


Call new method

Recompile

Add new method

Compile


No recompile of subclasses required when:• Methods / data is added to

super class

• Only implementation changes, not signature

When subclass accesses new methods and data, must recompile

AA

BB EE

FF

KK

JJ

HH

GGDD

CC

II



COMPILER: MULTI-COMPILE = TRUE• Uses cache to store classes

already compiled in session• “Cache” cleared when set to

FALSE• OE Architect uses this

option

Otherwise COMPILE builds full class hierarchy – no timestamp check

Total files compiled:

MULTI-COMPILE = FALSE: 25

MULTI-COMPILE = TRUE: 8

AA

BB

EE FF HHGG

DDCC

Build procedures (make.p)


Recommended Coding Standards

Always use packages in your type name: Acme.DAOrder• First node is your company name

Class and Interface names use CamelCase starting with uppercase letter• Interface names start with leading “I”: Acme.IList

Methods and data member use camelCase with lowercase first letter

Follow rules for encapsulation, abstraction, and delegation


In Summary

Object-oriented ABL supports standard OO design patterns – abstraction, encapsulation, inheritance, polymorphism

OO functionality still coming• Overloading

• Properties

• Error handling

• Remote Objects

• CLASS-GLOBAL (Static)

• Strongly-typed events


Related Sessions

DEV–1: Introduction to Object–Oriented Language Concepts and Programming in OpenEdge ABL

MOVE–11: Using Classes and Procedures in OpenEdge 10


Questions?


Thank you foryour time

DEV-6: Advanced Object-Oriented Programming in the ABL Evan Bleicher [email protected] Senior...

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