The code here was assuming that if the beatmap which is having changes
copied across does not exist within the `BeatmapSet.Beatmaps` list, it
was not yet persisted to realm.
In some edge case, it can happen that the beatmap *is* persisted to
realm but not correctly attached to the beatmap set. I don't yet know
how this occurs, but it has caused loss of data for at least two users.
The fix here is to check realm-wide for the beatmap (using its primary
key) rather than only in the list. We then handle the scenario where the
beatmap needs to be reattached to the set as a seprate step.
---
This does raise others questions like "are we even structuring this
correctly? couldn't a single beatmap exist in two different sets?"
Maybe, but let's deal with that if/when it comes up.
It seems that no usages of `BeatmapSetInfo` detaches require files - a
`WorkingBeatmap` is always obtained before doing further lookups.
Therefore we can omit this include unless the detaching object is a
`BeatmapInfo`. A refetch is performed when retrieving a
`WorkingBeatmap` to complete the equation.
This may not be the cleanest solution, but there don't seem to be any
way towards this either.
- `UseDestinationValue` has been inherited by default as noted in
https://docs.automapper.org/en/stable/10.0-Upgrade-Guide.html#usedestinationvalue-is-now-inherited-by-default, and its behaviour in this case would be using the nested **managed** realm object for the destination member rather than creating an unmanaged version.
- `MaxDepth` already sets `PreserveReferences` so there's no point of using it.
- `MaxDepth` should probably not be set for all maps, only for those with
cyclic references, to avoid the expensive overhead of `PreserveReferences`, as mentioned in https://docs.automapper.org/en/stable/5.0-Upgrade-Guide.html#circular-references.
That aside, `MaxDepth` should actually only be set to `1` for
`BeatmapSetInfo` mapping, because we don't want AutoMapper to create a
nested instance of `BeatmapSetInfo` in each mapped/detached beatmap, but
for some reason, doing that will cause automapper to not map any beatmap
inside the set and leave it with 0 beatmaps.
While on the other hand, using `MaxDepth(2)` for `BeatmapSetInfo` works,
but creates an unused instance of a `BeatmapSetInfo` inside each mapped
beatmap, which may not be ideal.
For `BeatmapInfo`, it has to be `MaxDepth(2)`, in which the first
`BeatmapInfo` depth would be itself (when detaching a beatmap), and the
second would be nested beatmaps inside the mapped/detached
`BeatmapSetInfo` within the beatmap. (note that when detaching a beatmap
set, the unused instance of `BeatmapSetInfo` within each beatmap of that
beatmap set doesn't also have a list of unused beatmaps as one might expect from the depth specification, it surprisingly has 0 beatmaps)
This causes it to create an unused instance of `BeatmapInfo` in the beatmap set resembling the root mapped/detached beatmap, but that one might be inevitable.
