Dependent object class and subclass mapping to relational data store

Abstract

A method and system for mapping a persistent dependent object between object-oriented schema and relational data store schema. Prior to application program run-time, schema mapping code is generated that defines a logical combination of null and non-null columns in the relational tables for each dependent class and dependent subclass. The code maps each instance variable of each class and subclass of the dependent to one column of the relational data store schema. The code maps a null value to each column for which a dependent subclass has no corresponding instance variable. At run-time, an application program may invoke the services of a schema map object, which in turn calls an object database driver such as ODBC to store an object in the data store or retrieve an object from the data store. In response to such calls referencing an object, the object database driver accesses the data store and associates the data elements with instance variables of the object in accordance with the mapping defined by the mapping code. The subclasses of the dependent are determined by comparing the pattern or combination of null values and non-null values read from the columns corresponding to each class and subclasses to that which the mapping code defines for each class and subclass. The application program, having been provided with the class and subclasses of the dependent, may then store the (non-null) values read by the driver into the instance variables of the object.