HoudahEOControl

The HoudahEOControl framework builds upon Apple’s EOControl framework as well as upon the HoudahFoundation framework. It intentionally does not rely on the EOAccess framework. Indeed the EOAccess layer is only one of several possible persistence layers EOControl may work with. Having a business layer dependant on EOAccess would introduce assumptions as to which persistence layer is used. Most notably such a business layer could no longer be used in the context of JavaClient applications where persistence is handled by the EODistribution framework. Following this logic, the ControlUtilities class appears as the most important class of the framework. It is in a way a sibling of Apple’s EOUtilities class. It actually re-implements all of EOUtilities’ methods that could be written without a dependency on the EOAccess layer. To this it adds a set of its own utility methods. You will find yourself using this class quite often: you should prefer it to EOUtilities in your business layer so as to prevent a dependency on the access layer.

The bulk of the HoudahEOControl code is made of custom qualifiers. Qualifiers describe criteria used to restrict the selection of objects. The WebObject frameworks provide a set of frequently used qualifiers: EOKeyValueQualifier, EOKeyComparisonQualifier, EOAndQualifier, EOOrQualifier and EONotQualifier. The HoudahEOControl framework adds quite a few custom qualifiers to this set. These are best documented by their respective JavaDoc. These qualifiers are meant as actual useful additions to the frameworks. They however also serve as examples and starting point for you to implement your own.

The ChangeNotificationCenter and related classes allow for caching derived values that are computed at display time. The owner of the cache may register for notifications of changes to values the cache derives from.