Simple Form input to generate multiple selects

rails_simple_form_array_many_select_input.rb

# frozen_string_literal: true

# To use with a ActiveRecord array column for instance:
#     add_column :myobjects, :features, :integer, array: true, default: []
#
# Based on https://tenforward.consulting/blog/integrating-an-array-column-in-rails-with-simple-form
class ArraySelectInput < SimpleForm::Inputs::CollectionSelectInput
  def input(wrapper_options = nil)
    label_method, value_method = detect_collection_methods

    merged_input_options = merge_wrapper_options(input_html_options, wrapper_options)

    name = "#{object_name}[#{attribute_name}][]"

    select_options = merged_input_options.merge(name: name)

    existing_values = Array(object.public_send(attribute_name)).map do |item|
      build_select_item(item, select_options, label_method, value_method)
    end

    existing_values.push build_select_item(nil, select_options, label_method, value_method)
    existing_values.join.html_safe
  end

  def build_select_item(value, select_options, label_method, value_method)
    input_options_with_value = input_options.merge(selected: value)
    @builder.collection_select(
      attribute_name, collection, value_method, label_method,
      input_options_with_value, select_options
    )
  end
end

rails_simple_form_array_many_select_input_controller.rb

class MyController < ApplicationController    
  def my_params
      p = params.require(:myobject).permit(
        features: []
      )
      # You may want to remove empte values, and  to keep only unique values
      p[:features] = p[:features].reject(&:empty?) #.uniq
      p
    end
end