Module dependencies

Introduction to Module Dependencies

As the overall modularity of PostNuke increases and the modules architecture moves away from large, monolithic modules to smaller, leaner single purpose modules it becomes necessary to provide a means by which site administrators can be informed of any dependencies for modules which they might add to or remove from a site.

PostNuke 0.80 introduces a simple but effective dependencies system that performs two main tasks

1. Before a module is initialized a list of modules upon which this module depends will be presented to the user. The module cannot be initialized if any required dependencies are not met.
2. Before a module is removed a list of modules which are dependent on this module will be presented to the user. The module cannot be removed prior to removal of any dependent modules.

The system provides three levels of dependencies

1. PNMODULE_DEPENDENCY_REQUIRED - a required dependency. This module will not function without its dependency.
2. PNMODULE_DEPENDENCY_RECOMMENDED - a recommended dependency. While this module will function without its dependency it's recommend that this dependency is also available.
3. PNMODULE_DEPENDENCY_CONFLICTS - a conflicting module. This module conflicts with another already present in the system. It's unlikely that this dependency level will ever be used but is present for completeness.

Module dependencies are stored in a single database table <table_prefix>_module_dependencies. This table is populated when the regenerate modules function is activated. At each regeneration of the modules list the dependencies table is emptied and repopulated.

Defining a Module Dependency

Module dependencies are defined via an additional field, $modversion['dependencies'], in the module version file - pnversion.php. The additional field is a array of dependencies. Each dependency itself is an array containing the module name, minimum and maximum versions and the type of dependency.

A sample dependency can be seen in the PostNuke 0.80 system package with the Categories module which is dependent on the ObjectData? module. The dependencies entry in the version file looks like

This dependency indicates that the Categories module is dependent on any version of the ObjectData? data module after v1.0 and that it's required for the Categories module to operate.

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