Reactive object queries: consistent views in object-oriented languages
Stefan Lehmann, Tim Felgentreff, Jens Lincke, Patrick Rein, Robert Hirschfeld · 2016
Maintaining consistency between data throughout a system using scattered, imperative code fragments is challenging. Some mechanisms address this challenge by making data dependencies explicit. Among these mechanisms are reactive collections, which define data dependencies for collections of objects, and object queries, which allow developers to query their program for a subset of objects. However, on their own, both of these mechanisms are limited. Reactive collections require an initial collection to apply reactive operations to and object queries do not update its result as the system changes. Using these two mechanisms in conjunction allows each to mitigate the disadvantage of the other. To do so, object queries need to respond to state changes of the system. In this paper, we propose a combination of both mechanisms, called reactive object queries. Reactive object queries allow the developer to declaratively select all objects in a program that match a particular predicate, creating a view. Additionally, views can be composed of other views using reactive operations. All views are automatically updated when the program state changes. To better integrate with existing imperative systems, we provide fine-grained events signaling view updates. We implemented the proposed concepts in JavaScript. Our initial experience with example applications shows that the combined concept eases the integration of reactive mechanisms with object-oriented environments by avoiding scattered update code.