Using Caché Objects - InterSystems Documentation

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Object-Oriented Database Development Classes provide structure and organization to applications. In particular, classes make it possible to divide the implementation of large applications among developers or teams of developers with reasonable assurance that their work will function when later integrated. An important feature of Caché is that new classes can be defined at runtime; that is, an application can extend itself by creating and using new classes as it runs. 2.2 Abstraction and Modeling Data abstraction is the process of taking the essential details of real-world entities (such as employees, invoices, documents) and defining from them representations that can be used within a software application. Object modeling is the process of taking a data abstraction and representing it as a set of classes, where each class defines the properties and behaviors of a specific entity. A set of behaviors defined for a class is typically referred to as an “interface” . Abstraction and modeling are at the heart of object-oriented programming. Using an object model, you can define application components that are analogs of the real-world entities your application works with. The beauty of an object model is that it is rich enough to model complex entities in a natural way: a book with a set of related chapters, for example. Contrast this with traditional relational database design where the data representation of real-world entities must be constrained to fit into 2–dimensional tables and there is no mechanism for associating behavior with data. 2.3 Inheritance and Polymorphism Inheritance is the process of taking an existing class and specializing it (changing aspects of its behavior) for new circumstances. Specifically this is done by specifying one or more super classes when creating a new class. The new class will inherit all of the data and behavior of its superclass. In addition the new class can add additional data and behavior or selectively replace (override) the behaviors inherited from its super class. Polymorphism is the ability to invoke the same method on objects of different types (but with a common superclass). Each object executes its own specific implementation of the method. This allows you to use new object types within existing applications without having to modify the applications. 10 Using Caché Objects
Encapsulation Caché exploits inheritance in several ways, including: • Extents—persistent classes derived a common superclass are stored within a common extent in the database. For example, you can store instances of Person as well as its subclass, Student, in the same extent. When an application asks for a list of all persons, it will get the persons as well as the students (since a student is a person). If the application asks for students, then only student (with any additional properties they define) are returned. This automatic behavior is difficult to achieve using the relational model. • Method Generators—Caché includes the concept of method generators: methods that are, in fact, programs that create method implementations. Using method generators it is possible to create classes that automatically generate application-specific code for different circumstances. 2.4 Encapsulation Encapsulation refers to the process of keeping the external representation of an entity—properties and methods—independent from the entity's actual implementation. The idea is that users of an entity (such as other parts of an application) can make use of it without knowledge of its internal workings and are immune from changes in its implementation. Object-oriented programming simplifies the process of encapsulation through the use of classes which, by definition, encapsulate behavior. An object-oriented database extends this concept to data stored within a database in two important ways: 1. Properties encapsulate data: it is possible to change the database while maintaining the same property interface. For example, a property may be redefined to be no longer stored but to be the result of a calculation performed on other properties. Users of such a property would see no difference. 2. Methods encapsulate behavior: when a persistent object is loaded from the database it is automatically associated with the methods defined for its class. You can change the implementation of such methods independently of both the data in the database and any users of these methods. Using Caché Objects 11
Page 1 and 2: Using Caché Objects Version 5.2 01
Page 3 and 4: Table of Contents 1 Introduction to
Page 5 and 6: 7 Properties ......................
Page 7 and 8: 13.1 Inheritance and SQL ..........
Page 9 and 10: 20.8 %OnNew .......................
Page 11 and 12: List of Figures Embeddable Objects
Page 13 and 14: 1 Introduction to Caché Objects Th
Page 15 and 16: 1.2 Class Definitions and the Class
Page 17 and 18: Development Tools Caché Class Libr
Page 19 and 20: • The Caché EJB Binding—a vers
Page 21: 2 Object-Oriented Database Developm
Page 25 and 26: 3 The Caché Object Model The Cach
Page 27 and 28: Referring to an Object — OREF, OI
Page 29 and 30: Types of Classes 3.2.1 Transient Ob
Page 31 and 32: Types of Classes Embeddable Objects
Page 33 and 34: A class inherits all of the specifi
Page 35: 2. It resolves inheritance—it det
Page 38 and 39: Caché Classes • Class Parameters
Page 40 and 41: Caché Classes ClientDataType Descr
Page 42 and 43: Caché Classes Internally, this wor
Page 44 and 45: Packages Class Packages Any of thes
Page 46 and 47: Packages Letting the compiler resol
Page 48 and 49: Packages • “%Library” —any
Page 50 and 51: Methods where count and state are d
Page 52 and 53: Methods 6.4 Method Language You hav
Page 54 and 55: Methods 6.6 Instance and Class Meth
Page 56 and 57: Methods Write dog.Speak() Which cou
Page 58 and 59: Properties 7.1 Property Keywords Yo
Page 60 and 61: Properties Property Behavior The pr
Page 62 and 63: Properties 7.5 Attribute Properties
Page 64 and 65: Properties You can manipulate a col
Page 67 and 68: 8 Class Queries Class queries provi
Page 69 and 70: Query Basics Final Specifies that s
Page 71 and 72: Caché ObjectScript. These queries
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The data in Row is the result of ex
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9 Indices Indexes provide a mechani
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Index Collation 9.2 Index Collation
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10 Using Objects with Caché Object
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Executing Methods 10.1.3 Executing
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Opening Objects 10.3 Opening Object
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where oref is the OREF of the speci
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For example, to populate the Home p
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change the second vaccination recor
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There are two types of array proper
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Saving Objects 10.5 Saving Objects
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mation. Again, this method deletes
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Set rset = ##class(%ResultSet).%New
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Executing Queries // Create a Resul
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Data Types 11.1 Available Types Cac
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Data Types • INDEXSUBSCRIPTS —
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Data Types CLIENTDATATYPE Values Va
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Data Types SQLCATEGORY Values Value
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Data Types The property is restrict
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Object Persistence 1. Its primary (
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Object Persistence Note: In a multi
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Object Persistence // Open person "
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Object Persistence For example: //
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Object Persistence If a persistent
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Object Persistence The storage clas
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13 Objects and SQL A key aspect of
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The Object-SQL Projection 13.2 The
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The Object-SQL Projection 13.2.2.1
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The Object-SQL Projection • The p
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If the list for a particular instan
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Triggers are, however, fired by the
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14 Relationships A relationship is
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Relationship Basics the relationshi
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An Invoice class class MyApp.Invoic
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14.4 Persistent Behavior of Relatio
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Streams Stream data may be stored i
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Streams 15.2.2 Copying Data between
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Streams Set stream=##class(%Stream.
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16 Class Projections Class projecti
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RemoveProjection The RemoveProjecti
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17 Object Synchronization Object sy
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About Updates • If two changes re
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About Updates Two Synchronized Data
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• classname is a quoted string th
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Set Status = TargetSyncSet.Import(f
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18 Method Generators A powerful fea
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Method Generator Context 6. It copi
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Implementing Method Generators 3. A
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The Caché Data Population Utility
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Using Callback Methods Since differ
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Using Callback Methods ReturnValue
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Using Callback Methods 20.6 %OnDele
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Using Callback Methods 20.10 %OnRol
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21 Object-Specific ObjectScript Fea
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##this Syntax >Do ##class(Package.C
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##super Syntax 21.4 ##super Syntax
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You can override a property's defau
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Dynamic Dispatch 22.2 Content of Me
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Dynamic Dispatch %DispatchMethod ca
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23 Class Definition Classes The Cac
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You can get detailed information ab
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Internet Classes addressed to , its
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Internet Classes For more informati
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Object Concurrency Setting 1 2 3 4
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Object Concurrency Note: You can us
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