dynamic-select2.rb

app/assets/javascripts/custom.js
$(document).ready(function() {
  let arraySelect2 = [".select2-yourvarname"]

  function select2Dynamic(name) {
    let id = $(name).attr("data-id")
    let text = $(name).attr("data-name")

    $(name).select2({
      placeholder: "Select Data",
      allowClear: true,
      ajax: {
        url: $(name).attr("data-uri"),
        dataType: "json",
        data: function (params) {

          return {
            term: params.term || "",
            page: params.page || 1
          }
        }
      }
    })

    if (id != null && text != null) {
      let data = {id: id, text: text}
      let newOption = new Option(data.text, data.id, true, true)

      $(name).append(newOption).trigger('change')
    }
  }

  arraySelect2.forEach(function(name) {
    select2Dynamic(name)
  })
})


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app/views/cities/_form.html.erb
<%= f.select(:city_id, options_for_select([], f.object.try(:city_id)), { include_blank: 'Select City' }, { class: 'form-control select2-city',
    'data-uri': address_admin_somethings_path(action_type: 'cities'), 'data-name': "#{@district.city.present? ? @district.city.name : ''}",
    'data-id': "#{@district.city.present? ? @district.city.id : ''}" }) %>


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app/controllers/concerns/controller_helper.rb
def get_json(klass)
  page = params[:page].to_i || 1
  per_page = 5
  offset = (page - 1) * per_page
  code_or_name = klass.to_s == "SpecificClassUseCode" ? "code" : "name"
  data = params[:term].present? ? klass.where("#{code_or_name} ilike ?", "%#{params[:term]}%").order(name: :asc).offset(offset).limit(per_page) :
         klass.order(name: :asc).offset(offset).limit(per_page)
  data_count = klass.count
  end_count = offset + per_page
  more_page = data_count > end_count

  results = {
    results: select2_api(data),
    pagination: {
      more: more_page
    }
  }

  render json: results, status: :ok
end

def select2_api(data)
  data.map do |data|
    cache data do
      {
        id: data.id,
        text: data.class.name == "PostalCode" ? data.code : data.name
      }
    end
  end
end



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app/controllers/admin/somethings_controller.rb
include ControllerHelper

def address
  if params[:action_type] == "cities"
    get_json(City)
  end
end