Allow nested_select multiple: true option

[shartep]

I find this PR https://github.com/platanus/activeadmin_addons/pull/72 (created by @groony ) it looks like this feature should be already present, bu I did not find any documentation on how to activate and use it, I try:

f.input :city_ids, as: :nested_select, multiple: true,
                  level_1: { attribute: :country_id },
                  level_2: { attribute: :region_id },
                  level_3: { attribute: :city_ids }

or

f.input :city_ids, as: :nested_select, 
                  level_1: { attribute: :country_id },
                  level_2: { attribute: :region_id },
                  level_3: { attribute: :city_ids, multiple: true }

and it is not works for me, cities select still not provide ability to select several cities.

It will be very useful to add ability to use nested_select with multiple: true option for has_many and has_and_belongs_to_many associations. Here is workflow, related to example in README:

• user select Country
• user select Region
• user can select several Cities using Select2 multiple feature

More complicated variant: in addition to workflow above:

• user select new Country
• user select another Region
• user can add several new Cities to already selected list (previously selected cities shouldn't be removed)

And one more complicated case: use multiple: true for each level, so user can select several Countries, and several Regions to see Cities related to one of selected Region

[mashedkeyboard]

I was just thinking about this same thing - would be really useful to see support for this use case.

[gen1321]

I do have working solution on this problem, but it needs https://github.com/platanus/activeadmin_addons/pull/264 to work properly

I will make pr as soon as 264 pr will be merged

[rjherrera]

@gen1321 Nice! I asked the author of that PR to rebase his branch, so we can merge it but it seems that it was too late. Maybe if you have a working solution for that PR also, we could review it and eventually merge it.

[jgmontoya]

Hey @gen1321 just letting you know that #264 has been merged!

[sleivav]

@gen1321 do you still plan sending that PR? If you don't, I'll try to implement this myself