Using Caché Objects - InterSystems Documentation

13
Objects and SQL
A key aspect of Caché functionality is that it makes data visible both as objects and relational
tables: data that composes a set of class instances is projected as one or more relational tables.
In its relational form, this data is available for use with Caché SQL, which provides highperformance
relational access to the Caché data engine.
This chapter describes how objects are projected for SQL access; it assumes knowledge and
experience with SQL. For more information on classes and their definition, see the chapter
Classes.
The interconnection of Caché SQL and Caché objects allows your application to refer to a
class instantiation either as a particular object or as a part of a relational table. Generally, a
class definition's relational projection is a table: instantiations are rows within the table and
properties are columns within the table.
Note:
Certain features of a Caché class definition may not be accessible as both object and
relational features, due to the nature of the object and relational models (rather than
the limitations of Caché or any other tools).
13.1 Inheritance and SQL
Since inheritance is not part of the relational model, the Class Compiler projects a “flattened”
representation of the class as a relational table. The projected table contains all the appropriate
fields for the class, including those that are inherited. Hence, the projection of a subclass is
a table composed of:
Using Caché Objects 113