Using Caché Objects - InterSystems Documentation

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Object Persistence The storage class used by a persistent class is specified by a Storage Definition. A storage definition contains a set of keywords and values that define a storage class as well as additional parameters used by the storage interface. A persistent class may contain more than one storage definition but only one can be active at a time. The active storage definition is specified using the class' StorageStrategy keyword. By default, a persistent class has a single storage definition called “Default” . 12.4.1 The %CacheStorage Storage Class %CacheStorage is the default storage class used by persistent objects. It automatically creates and maintains a default storage structure for a persistent class. Whenever you create a new persistent class, it will automatically use the %CacheStorage storage class. The %CacheStorage class lets you control certain aspects of the storage structure used for a class by means of the various keywords in the storage definition. Refer to the Storage Keywords section of the Class Definition Reference for details on the various storage keywords. 12.4.2 The %CacheSQLStorage Storage Class The %CacheSQLStorage is a special storage class that uses generated SQL SELECT, INSERT, UPDATE, and DELETE statements to provide object persistence. The %CacheSQLStorage is typically used for: • Mapping objects to preexisting global structures used by older applications. • Storing objects within an external relational database using the SQL Gateway. The %CacheSQLStorage is more limited than %CacheStorage. Specifically, it does not automatically support Schema Evolution or multi-class extents. 12.5 Schema Evolution The %CacheStorage storage class supports automatic schema evolution. When you compile a persistent (or serial) class that uses the default %CacheStorage storage class, the Class Compiler will analyze the properties defined by the class and automatically add them 110 Using Caché Objects
If you would like to see schema evolution in action, then try the following: Schema Evolution 1. Start Caché Studio and create a new persistent class with one or more properties in it. 2. Compile the class and then view the automatically generated storage definition (as XML text) for the class using the View Storage command on the View menu. Alternatively, you can see a more graphical representation of storage using the Class Inspector. Click on Storage in the Inspector, click in “Default” in the list of Storage definitions, click on Data Nodes in the keyword list, and click on the browse button (...) that appears. This invokes a graphical storage editor. Within the generated storage for your class, you will see the pseudo-property %%CLASSNAME. This is a placeholder for the class name of any future subclasses you may derive from your class and is used to tell the type of objects stored in the database. For the root class of an extent, this value is always empty. 3. Add one or more new properties to your class and compile it again. Notice that these new properties have been added to your storage definition automatically and in way that is compatible to the previously existing storage. 12.5.1 Resetting the Storage Definition During the development process, you may make many modifications to your persistent classes: adding, modifying, and deleting properties. As a result, you may end up with a fairly convoluted storage definition as the Class Compiler attempts to maintain a compatible structure after each change. If you would like to have the Class Compiler regenerate a cleaner storage structure, simply delete the storage definition for the class and recompile it. You can do this as follows: 1. Open the class in Caché Studio, 2. Right-click on the default Storage definition in the Class Inspector, 3. Invoke the Delete command in the popup menu, and, 4. Compile the class. This will cause the Class Compiler to generate a new storage definition for the class. Using Caché Objects 111
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Using Caché Objects Version 5.2 01
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Table of Contents 1 Introduction to
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7 Properties ......................
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13.1 Inheritance and SQL ..........
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20.8 %OnNew .......................
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List of Figures Embeddable Objects
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1 Introduction to Caché Objects Th
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1.2 Class Definitions and the Class
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Development Tools Caché Class Libr
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• The Caché EJB Binding—a vers
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2 Object-Oriented Database Developm
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Encapsulation Caché exploits inher
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3 The Caché Object Model The Cach
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Referring to an Object — OREF, OI
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Types of Classes 3.2.1 Transient Ob
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Types of Classes Embeddable Objects
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A class inherits all of the specifi
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2. It resolves inheritance—it det
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Caché Classes • Class Parameters
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Caché Classes ClientDataType Descr
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Caché Classes Internally, this wor
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Packages Class Packages Any of thes
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Packages Letting the compiler resol
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Packages • “%Library” —any
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Methods where count and state are d
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Methods 6.4 Method Language You hav
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Methods 6.6 Instance and Class Meth
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Methods Write dog.Speak() Which cou
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Properties 7.1 Property Keywords Yo
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Properties Property Behavior The pr
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Properties 7.5 Attribute Properties
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Properties You can manipulate a col
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8 Class Queries Class queries provi
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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 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
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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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