Add bulk repositioning API and document deferred unique constraints

[ollym]

Thanks for the gem. We wanted to introduce repositioning code that allows for bulk changes to the position that would also take care of position conflicts during the bulk reordering.

• add update_<column>_in_order_of! for bulk reordering by id list or weight hash
• refactor healer to support bulk repositioning and scoped normalization
• document Rails 7.1+ deferred unique keys and bulk reposition usage

Made sense to make it part of the "Healer" as they perform similar functionality.

[ollym]

I've just added partial repositioning which again we needed in our implementation, so like:

# positions: A:1, B:2, C:3, D:4, E:5
Item.update_position_in_order_of!([d.id, b.id])
# positions: A:1, D:2, C:3, B:4, E:5

[brendon]

Hi @ollym, thanks for this. Just letting you know I’m away on holiday at the moment but will look at this when I return :) Hope that’s ok? :)

[ollym]

@brendon tests pass for me locally, so unclear why it's not working on CI

$ DB=postgresql rake test
Run options: --seed 61593

# Running:

....................................................................................................................................................................................

Finished in 6.854978s, 26.2583 runs/s, 460.1036 assertions/s.

180 runs, 3154 assertions, 0 failures, 0 errors, 0 skips

[brendon]

Looks like something to do with composite primary keys? Will have a closer look when I get back :)

[brendon]

Got the tests running. Might look at cherrypicking those commits into main and then will review this code in a week or so :)