Introduction to Caché
Objects, SQL, and the Unified Data Architecture
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A powerful and unique feature of Caché is its unique Unified Data Architecture that provides simultaneous, high-performance object and relational access to data stored within Caché.

Unified Data Dictionary
Within Caché, you can model your application components as objects. Objects are organized by classes which define the data (properties) and behavior (methods) of the object.
Unified Data Architecture
The meta-information, or definition, of each class is stored within a common repository referred to as the Caché class dictionary. The class dictionary is itself an object database, stored within Caché, whose contents can be accessed using objects. The class dictionary, by means of a class compiler, defines the storage structure needed by persistent objects and converts class definitions into parallel sets of executable code that provide both the object and relational access to this storage structure. By means of this architecture, the object and relational code paths are efficient and automatically synchronized with one another.
Class definitions can be added to the class dictionary in a number of ways:
Flexible Storage
The Caché object model differs from those of programming languages in that in addition to properties and methods, you can specify storage-related behavior such as indices, constraints, and storage structure.
The storage structure used by persistent objects is independent of the logical definition of a class and is quite flexible: developers can use the default structures provided by the class compiler or they can tune the structures for specific cases.
Caché includes a full-featured, next-generation object database specifically designed to meet the needs of complex, transaction oriented applications. The Caché object model includes the following features:
The Caché object functionality is not a separate part of Caché; it is a central part of Caché programming and is fully integrated with relational access described elsewhere. However, for those who are interested specifically in object-oriented programming, the manual Using Caché Objects discusses Caché programming from this point of view.
Defining Classes
The simplest and most common way to define classes within Caché is to use the Studio development environment. The Studio lets you define classes either using a simple text format within a syntax-coloring editor or by using a graphical point-and-click interface. These two views are interchangeable and are automatically synchronized.
Here is the definition of an extremely simple persistent object, Component, as seen within Studio:
Class MyApp.Component Extends %Persistent
Property TheName As %String;
Property TheValue As %Integer;
This class is defined as a persistent class (that is, it can store itself within a database). In this case, the Caché-provided, %Persistent class (system class names start with a “%” character to distinguish them from application classes) provides all the needed persistence code via inheritance. The class belongs to the package, “MyApp”. Packages group related classes together and greatly simplify development of large applications. The class defines two properties: TheName, which has a string value, and TheValue, which has an integer value.
From within ObjectScript code, such as within a method, you can use this object syntax to manipulate instances of Component object:
 // Create a new component
 Set component = ##class(MyApp.Component).%New()
 Set component.TheName = "Widget"
 Set component.TheValue = 22

 // Save the new Component to the database
 Do component.%Save()
Using Basic, you can define a method to manipulate instances of the Component object:
' Create a new component
component = New Component()
component.TheName = "Widget"
component.TheValue = 22

' Save the new Component to the database
At this point, a new instance of Component is stored within the database with a system-assigned unique object identifier. You can later retrieve this object by opening it (using its object identifier):
' Open an instance and double its value:
component = OpenId Component(id)

component.TheValue = component.TheValue * 2
You can perform the exact same operations using native Java, C++, or other Caché client bindings. The class compiler can generate, and synchronize, any additional code required to access objects externally. For example, if you are using Caché with Java, you can specify that the class compiler automatically generate and maintain Java proxy classes that provide remote access to persistent database classes. Within a Java program you can use this object naturally:
// Get an instance of Component from the database
component = (MyApp.Component)MyApp.Component._open(database, new Id(id));

// Inspect some properties of this object
System.out.println("Name: " + component.getTheName());
System.out.println("Value: " + component.getTheValue());
Caché SQL is a full-featured relational database engine that is fully integrated with the Caché object technology. In addition to standard SQL-92 features, Caché SQL offers:
The Object/Relational Connection
All components within the Caché dictionary are defined as classes. The class compiler automatically projects persistent classes as relational tables. For every object feature, there is a corresponding relational equivalent, as illustrated in the following table:
Relational View of Object Features
Object Feature Relational Equivalent
Package Schema
Class Table
Object instance Row within a table
Property Column
Relationship Foreign key
Embedded object Multiple columns
Method Stored procedure
Index Index
When Caché loads SQL DDL (Data Definition Language) statements, it uses the inverse of this projection to create classes that correspond to relational tables.
To demonstrate the object-to-relational projection, consider a simple example. Here is the definition of a simple, persistent Person class (part of a package called “MyApp”) containing two properties, Name and Home:
Class MyApp.Person Extends %Persistent
Property Name As %String(MAXLEN=100);
Property Home As Address;
The Person class gets its persistent behavior from the %Persistent superclass provided with Caché. The Name property is defined as a simple String of up to 100 characters.
The Home property illustrates the use of complex, user-defined data types, in this case the Address class, which is defined as:
Class MyApp.Address Extends %SerialObject
Property City As %String;
Property State As %String;
The Address class is derived from the %SerialObject superclass. This class provides the ability to serialize itself (convert itself to a single-string representation) and embed itself within another containing class (as with the Person class).
When viewed via SQL, the Person class has the following structure:
SQL View of the Person class: SELECT * FROM Person
ID Name Home_City Home_State
1 Smith,John Cambridge MA
2 Doe,Jane Dallas TX
Note that the object identifier is visible as a column. In addition, the fields of the embedded Address object are projected as separate fields. These fields are given the synthetic names Home_City and Home_State and behave exactly as if they were defined as two individual fields.
Inheritance and SQL
Inheritance is an important feature within object-based systems and is completely lacking within relational databases. Caché SQL makes it possible to use the power of inheritance using standard relational constructs. For example, we can derive a new Employee class from the Person class used in the previous example:
Class MyApp.Employee Extends Person
Property Salary As %Integer(MINVAL=0,MAXVAL=100000);
This new class extends the Person class by adding an additional property, Salary.
When viewed via SQL, the Employee class has the following structure:
SQL View of the Employee class: SELECT * FROM Employee
ID Name Home_City Home_State Salary
3 Divad, Gino Irvine CA 22000
Notice that all of the inherited properties are available as columns. Also note that only rows that are actual instances of Employee are included. If we again ask for all Person instances:
Revised SQL View of the Person class: SELECT * FROM Person
ID Name Home_City Home_State
1 Smith,John Cambridge MA
2 Doe,Jane Dallas TX
3 Divad, Gino Irvine CA
In this case, we see that all the rows are returned because every Employee is defined to be an instance of Person. In this case, however, only the properties defined by Person are displayed.
Object Extensions to SQL
To make it easier to use SQL within object applications, Caché includes a number of object extensions to SQL.
One of the most interesting of these extensions is ability to follow object references using the reference (“–>”) operator. For example, suppose you have a Vendor class that refers to two other classes: Contact and Region. You can refer to properties of the related classes using the reference operator:
SELECT ID,Name,ContactInfo->Name
FROM Vendor
WHERE Vendor->Region->Name = 'Antarctica'
Of course, you can also express the same query using SQL JOIN syntax. The advantage of the reference operator syntax is that it is succinct and easy to understand at a glance.

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