Using Caché Objects - InterSystems Documentation

More documents

Recommendations

Info

The Caché Object Model This method creates an instance of Sample.Person and places a reference to it into the variable person. Then it creates another instance of Sample.Person and replaces the value of person with a reference to it. At this point, the first object is no longer referred to and is destroyed. At the end of the method, person goes out of scope and the second object is destroyed. You can test if a variable contains a valid OREF value using the ObjectScript $IsObject function: // Open an object that is in the database Set obj = ##class(Sample.Person).%OpenId(1) Write "Is (1) an object ",$IsObject(obj),! // Open an object that is NOT in the database Set obj = ##class(Sample.Person).%OpenId(-1) Write "Is (-1) an object ",$IsObject(obj),! 3.2 Types of Classes Caché supports a variety of class types for specialized behaviors. Classes are divided into data type classes and object classes. Data type classes represent literal values such as strings, integers, and dates; refer to the chapter on Data Types for more details. Data type classes are used to create literal properties of other objects. They do not have properties and cannot be instantiated. Object classes may have properties and can be instantiated. Most object class are subclasses of a system class called %RegisteredObject, which automatically provides much of an object's basic behavior. An object class has a rich set of default behaviors, which include the following: • Its instantiation triggers the automatic allocation of system memory for its properties. • Its instantiation triggers the automatic creation of a reference handle (OREF) for it. • It supports polymorphism. Object classes are further divided, according to their database behavior, into transient objects, persistent objects, and serial objects. A transient object (derived directly from the %RegisteredObject class) has no storage behavior; it exists only in memory. Persistent classes (derived the the %Persistent class) can be independently stored in a database. Serial objects (derived from the %SerialObject class) can be embedded within other objects; a serial object can only be stored to the database when it is embedded within another, persistent object. 16 Using Caché Objects
Types of Classes 3.2.1 Transient Object Classes Instantiations of classes derived from %RegisteredObject are known as registered or transient objects. These objects have a full set of built-in methods for controlling their in-memory behavior. (Most applications use persistent classes and embeddable classes rather than inheriting directly from %RegisteredObject.) Once you create an instance of a registered object, you can refer to it by its OREF (object reference). This system assigned value is transient; the value exists only while the object is in memory and is not guaranteed to be constant over different invocations. Registered objects use system allocated memory to store their values, and they support polymorphism. 3.2.2 Persistent Object Classes Instantiations of classes derived from %Persistent are known as persistent objects; these objects are registered objects that inherit from the %Persistent class and have their ClassType keyword set to “persistent” . Persistent objects have the ability to store themselves into the database. Loading a persistent object into memory from the database does not load any other objects that it refers to. As soon as a referenced object is referred to, however, it is automatically brought into memory (this is known as “swizzling” or “lazy loading” ). When a persistent object is used as a property, it is referred to as a “reference” property. For example, if Doctor and Patient are persistent classes, you can define an attribute in the Patient class that uses Doctor as its type: Property TheDoc As Doctor; The property, TheDoc, is a reference property. The first time this property is referenced: Set doc = patient.TheDoc the appropriate Doctor object is loaded from the database automatically. In this example, doc will contain an OREF to the loaded Doctor object. You can chain together as many references as you like within one expression: Set location = patient.TheDoc.Hospital.Address.City If any of the objects referenced in such an expression is missing (null), then the entire expression will return a null value (""). Using Caché Objects 17
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 and 22: 2 Object-Oriented Database Developm
Page 23 and 24: Encapsulation Caché exploits inher
Page 25 and 26: 3 The Caché Object Model The Cach
Page 27: Referring to an Object — OREF, OI
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
Page 73 and 74: The data in Row is the result of ex
Page 75 and 76: 9 Indices Indexes provide a mechani
Page 77 and 78: Index Collation 9.2 Index Collation
Page 79 and 80:
10 Using Objects with Caché Object
Page 81 and 82:
Executing Methods 10.1.3 Executing
Page 83 and 84:
Opening Objects 10.3 Opening Object
Page 85 and 86:
where oref is the OREF of the speci
Page 87 and 88:
For example, to populate the Home p
Page 89 and 90:
change the second vaccination recor
Page 91 and 92:
There are two types of array proper
Page 93 and 94:
Saving Objects 10.5 Saving Objects
Page 95 and 96:
mation. Again, this method deletes
Page 97 and 98:
Set rset = ##class(%ResultSet).%New
Page 99:
Executing Queries // Create a Resul
Page 102 and 103:
Data Types 11.1 Available Types Cac
Page 104 and 105:
Data Types • INDEXSUBSCRIPTS —
Page 106 and 107:
Data Types CLIENTDATATYPE Values Va
Page 108 and 109:
Data Types SQLCATEGORY Values Value
Page 110 and 111:
Data Types The property is restrict
Page 112 and 113:
Object Persistence 1. Its primary (
Page 114 and 115:
Object Persistence Note: In a multi
Page 116 and 117:
Object Persistence // Open person "
Page 118 and 119:
Object Persistence For example: //
Page 120 and 121:
Object Persistence If a persistent
Page 122 and 123:
Object Persistence The storage clas
Page 125 and 126:
13 Objects and SQL A key aspect of
Page 127 and 128:
The Object-SQL Projection 13.2 The
Page 129 and 130:
The Object-SQL Projection 13.2.2.1
Page 131 and 132:
The Object-SQL Projection • The p
Page 133 and 134:
If the list for a particular instan
Page 135 and 136:
Triggers are, however, fired by the
Page 137 and 138:
14 Relationships A relationship is
Page 139 and 140:
Relationship Basics the relationshi
Page 141 and 142:
An Invoice class class MyApp.Invoic
Page 143:
14.4 Persistent Behavior of Relatio
Page 146 and 147:
Streams Stream data may be stored i
Page 148 and 149:
Streams 15.2.2 Copying Data between
Page 150 and 151:
Streams Set stream=##class(%Stream.
Page 153 and 154:
16 Class Projections Class projecti
Page 155 and 156:
RemoveProjection The RemoveProjecti
Page 157 and 158:
17 Object Synchronization Object sy
Page 159 and 160:
About Updates • If two changes re
Page 161 and 162:
About Updates Two Synchronized Data
Page 163 and 164:
• classname is a quoted string th
Page 165 and 166:
Set Status = TargetSyncSet.Import(f
Page 167 and 168:
18 Method Generators A powerful fea
Page 169 and 170:
Method Generator Context 6. It copi
Page 171:
Implementing Method Generators 3. A
Page 174 and 175:
The Caché Data Population Utility
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Using Callback Methods Since differ
Page 184 and 185:
Using Callback Methods ReturnValue
Page 186 and 187:
Using Callback Methods 20.6 %OnDele
Page 188 and 189:
Using Callback Methods 20.10 %OnRol
Page 191 and 192:
21 Object-Specific ObjectScript Fea
Page 193 and 194:
##this Syntax >Do ##class(Package.C
Page 195 and 196:
##super Syntax 21.4 ##super Syntax
Page 197:
You can override a property's defau
Page 200 and 201:
Dynamic Dispatch 22.2 Content of Me
Page 202 and 203:
Dynamic Dispatch %DispatchMethod ca
Page 205 and 206:
23 Class Definition Classes The Cac
Page 207:
You can get detailed information ab
Page 210 and 211:
Internet Classes addressed to , its
Page 212 and 213:
Internet Classes For more informati
Page 214 and 215:
Object Concurrency Setting 1 2 3 4
Page 216 and 217:
Object Concurrency Note: You can us
show all

Using Caché Objects - InterSystems Documentation

Create successful ePaper yourself

Delete template?

Save as template?