Vikunja now uses one recursive CTE and a few optimizations to fetch all subscribers for a task or project. This makes the relevant code easier to maintain and more performant.
Before this fix, a project subscription object was added twice to the list of subscriptions for a task when the user did not subscribe to the task directly. This caused the user to receive a comment notification twice for a given task.
This was probably a regression from efde364224.
Resolves https://community.vikunja.io/t/e-mail-notification-twice/2740/18
Testing this locally resulted in improved response times from ~50ms to ~20ms when creating a project. It looks like even though the code running these sql queries uses different go routines, they affect each other (caused by IO or context switching?)
This change ensures already loaded projects are passed down when fetching their subscription instead of re-loading each project with a single sql statement. When loading all projects, this meant all projects were loaded twice, which was highly inefficient. This roughly added 25ms to each request, assuming the per page limit was maxed out at 50 projects.
Empirical testing shows this change reduces load times by ~20ms. Because the request is already pretty fast, this is ~30% of the overall request time, making the loading of projects now even faster
