Computed Properties and Cached Methods on Collections and Models

The concept of computed properties ( on the model ) or cached methods ( on the collection ) optimizes for cases where you call a method that performs calculations or some other operations whose value is dependent on the model and its underlying attributes.

Cached Methods on Luca.Collection

Luca provides a configuration API for Luca.Collection where you specify the method whose value you wish to cache, and the change events which get bubbled up from the models that would change the value, in essence expiring the cache. In addition to change events, standard events on the collection for when a model is added or removed will expire the cached value.

  _.def("MyCollection").extends("Luca.Collection").with
    name:"my_collection"

    cachedMethods:[
      "expensiveMethod:attributeOne,attributeTwo",
      "anotherExpensiveMethod"
    ] 

    expensiveMethod: ()->
      @map (model)-> model.get('attributeOne') + model.getAttribute('two')

    anotherExpensiveMethod: ()->
      @map (model)-> model.value()

In the example above, the expensiveMethod is dependent on the attributeOne and attributeTwo attributes on each of the models in the collection, therefor if any of these values change, the cache needs to be expired.

the anotherExpensiveMethod call is not dependent on any specific values, so will only expire any time a new model is added or removed, or the collection is reset.

Computed Properties on Luca.Model

  _.def("MyModel").extends("Luca.Model").with
    computed:
      "expensiveMethod" : ["dependencyOne","dependencyTwo"]

    expensiveMethod: ()->
      @get("dependencyOne") + @get("dependencyTwo")

In the example above, once expensiveMethod is called, its value will be cached and will be invalidated any time the dependencyOne or dependencyTwo attribute changes and triggers a change:dependencyTwo event.