implement reactive queries

[kukeiko]

What

Reactive queries - when a user issues a query, they can somehow mark them as being reactive. If marked that way, query should emit if any changes to its result have been made.

Example:

• user issues query "give me all songs from Artist X"
• a new song of Artist X is created
• query emits again so that the new song is included in its result

Why

Because:

• very convenient for the user to not have to manage re-executing queries
• it would allow a user of this library to use it for state management

Notes

need some form of protection against cyclic dependencies between reactive queries resulting in the browser crashing. for example, if we use this lib for state management, if we make changes to the stored entities based on the result of another query, that other query might trigger again, resulting in an endless loop.

[kukeiko]

an extremely basic and primitive form of reactive queries is implemented in the workspace. can't really stay the way it works now: on each change to the cached data, every reactive query is re-emitted, and a distinctUntilChanged() (with a custom comparator) is used to prevent endless loops