Type extension composition

Many types that are part of the core Resolwe framework contain logic that users of the framework may need to extend. To facilitate this in a controlled manner, the Resolwe framework provides a generic type extension composition system.

Making a type extendable

The composition system is very generic and as such can be used on any type. It provides a single method which allows you to retrieve a list of all registered extensions for a type or an instance of that type.

>>> composer.get_extensions(my_type_or_instance)
[<Extension1>, <Extension2>]

The type can then use this API to incorporate the registered extensions into its current instance however it chooses. Note that what these extensions are is entirely dependent upon the type that uses them.

For example, in the core Resolwe framework we make all index definitions extendable by using something like:

for extension in composer.get_extensions(attr):
    mapping = getattr(extension, 'mapping', {})

Writng an extension

On the other side, you can also define extensions for types that are using the above mentioned API. All extensions are automatically discovered during Django application registration if they are placed in a module called extensions in the given application.

Extensions can be registered using a simple API:

class MyExtension:

composer.add_extension('fully.qualified.type.Path', MyExtension)

Again, what the extension is depends on the type that is being extended. Now we describe some common extension types for types that are part of the Resolwe core.

Data viewset

It is possible to extend the filters of the Data viewset by defining an extension as follows:

class ExtendedDataViewSet:
    """Data viewset extensions."""
    filtering_fields = ('source', 'species', 'build', 'feature_type')

    def text_filter(self, value):
        return [
            Q('match', species={'query': value, 'operator': 'and', 'boost': 2.0}),
            Q('match', source={'query': value, 'operator': 'and', 'boost': 2.0}),
            Q('match', build={'query': value, 'operator': 'and', 'boost': 2.0}),
            Q('match', feature_type={'query': value, 'operator': 'and', 'boost': 1.0}),
composer.add_extension('resolwe.flow.views.data.DataViewSet', ExtendedDataViewSet)