application record: add array_attribute method.

Add `array_attribute` method that defines helper methods for converting
array attributes to or from strings.

app/controllers/pools_controller.rb

@@ -94,7 +94,7 @@ class PoolsController < ApplicationController
   private
 
   def pool_params
-    permitted_params = %i[name description category is_active post_ids]
+    permitted_params = %i[name description category is_active post_ids post_ids_string]
     params.require(:pool).permit(*permitted_params, post_ids: [])
   end
 end

app/models/application_record.rb

@@ -269,6 +269,37 @@ class ApplicationRecord < ActiveRecord::Base
     end
   end
 
+  concerning :AttributeMethods do
+    class_methods do
+      # Defines `<attribute>_string`, `<attribute>_string=`, and `<attribute>=`
+      # methods for converting an array attribute to or from a string.
+      #
+      # The `<attribute>=` setter parses strings into an array using the
+      # `parse` regex. The resulting strings can be converted to another type
+      # with the `cast` option.
+      def array_attribute(name, parse: /[^[:space:]]+/, cast: :itself)
+        define_method "#{name}_string" do
+          send(name).join(" ")
+        end
+
+        define_method "#{name}_string=" do |value|
+          raise ArgumentError, "#{name} must be a String" unless value.respond_to?(:to_str)
+          send("#{name}=", value)
+        end
+
+        define_method "#{name}=" do |value|
+          if value.respond_to?(:to_str)
+            super value.to_str.scan(parse).map(&cast)
+          elsif value.respond_to?(:to_a)
+            super value.to_a
+          else
+            raise ArgumentError, "#{name} must be a String or an Array"
+          end
+        end
+      end
+    end
+  end
+
   def warnings
     @warnings ||= ActiveModel::Errors.new(self)
   end

app/models/pool.rb

@@ -1,13 +1,15 @@
 class Pool < ApplicationRecord
   class RevertError < Exception ; end
 
+  array_attribute :post_ids, parse: /\d+/, cast: :to_i
+  belongs_to_creator
+
   validates_uniqueness_of :name, case_sensitive: false, if: :name_changed?
   validate :validate_name, if: :name_changed?
   validates_inclusion_of :category, :in => %w(series collection)
   validate :updater_can_change_category
   validate :updater_can_remove_posts
   validate :updater_can_edit_deleted
-  belongs_to_creator
   before_validation :normalize_post_ids
   before_validation :normalize_name
   after_save :update_category_pseudo_tags_for_posts_async
@@ -153,18 +155,6 @@ class Pool < ApplicationRecord
     self.post_ids = post_ids.uniq if is_collection?
   end
 
-  # allow assigning a string to post_ids so it can be assigned from the text
-  # field in the pool edit form (PUT /pools/1?post_ids=1+2+3).
-  def post_ids=(value)
-    if value.respond_to?(:to_str)
-      super value.to_str.scan(/\d+/).map(&:to_i)
-    elsif value.respond_to?(:to_a)
-      super value.to_a
-    else
-      raise ArgumentError, "post_ids must be a String or an Array"
-    end
-  end
-
   def revert_to!(version)
     if id != version.pool_id
       raise RevertError.new("You cannot revert to a previous version of another pool.")

app/views/pools/edit.html.erb

@@ -8,7 +8,7 @@
       <%= f.input :name, :as => :string, :input_html => { :value => @pool.pretty_name } %>
       <%= dtext_field "pool", "description" %>
       <%= dtext_preview_button "pool", "description" %>
-      <%= f.input :post_ids, as: :text, label: "Posts", input_html: { value: @pool.post_ids.join(" ") } %>
+      <%= f.input :post_ids_string, as: :text, label: "Posts" %>
       <%= f.input :category, :collection => ["series", "collection"], :include_blank => false %>
       <%= f.input :is_active %>
       <%= f.button :submit %>

app/views/pools/new.html.erb

@@ -7,7 +7,7 @@
     <%= simple_form_for(@pool) do |f| %>
       <%= f.input :name, :as => :string, :required => true %>
       <%= dtext_field "pool", "description" %>
-      <%= f.input :post_ids, as: :text, label: "Posts", input_html: { value: @pool.post_ids.join(" ") } %>
+      <%= f.input :post_ids_string, as: :text, label: "Posts" %>
       <%= f.input :category, :collection => ["series", "collection"], :include_blank => true, :selected => "", :required => true %>
       <%= f.input :is_active %>
       <%= f.button :submit, "Submit" %>