#67: Add json style field to content items

This field is intended for storing item-specific content styling
attributes that do not need to be referenced in migrations or
database queries. Items should take responsibility for initialising
and upgrading their own attributes.

app/models/concerns/katalyst/content/has_style.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module Katalyst
+  module Content
+    module HasStyle
+      extend ActiveSupport::Concern
+
+      # Style attribute allows items to define their own attributes for use in
+      # content styles. These attribute will be automatically mapped to json
+      # data which is stored and deserialized without needing to add columns.
+      class_methods do
+        def style_attributes(&)
+          style_class = Class.new(Katalyst::Content::HasStyle::StyleBase, &)
+          const_set(:Style, style_class)
+          attribute(:style, Katalyst::Content::Types::StyleType.new(style_class), default: -> { style_class.new })
+
+          style_class.attribute_names.each do |name|
+            define_method(name) { style.public_send(name) }
+            define_method(:"#{name}=") { |value| style.public_send(:"#{name}=", value) }
+          end
+
+          validate do
+            style.validate(validation_context)
+            style.errors.each do |error|
+              errors.add(error.attribute, error.type)
+            end
+          end
+        end
+      end
+
+      class StyleBase
+        include ActiveModel::Model
+        include ActiveModel::Attributes
+      end
+    end
+  end
+end

app/models/katalyst/content/item.rb

@@ -4,6 +4,8 @@ module Katalyst
   module Content
     # STI base class for content items
     class Item < ApplicationRecord
+      include HasStyle
+
       def self.config
         Katalyst::Content.config
       end

app/models/katalyst/content/types/style_type.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Katalyst
+  module Content
+    module Types
+      # Data serialization/deserialization for Katalyst::Content::Item style data
+      class StyleType < ActiveRecord::Type::Json
+        def initialize(type)
+          super()
+
+          @type = type
+        end
+
+        def serialize(value)
+          super(value.attributes)
+        end
+
+        def deserialize(value)
+          case value
+          when String
+            decoded = super
+            @type.new(**decoded) unless decoded.nil?
+          when Hash
+            @type.new(**value)
+          when HasStyle::StyleBase
+            value
+          end
+        end
+      end
+    end
+  end
+end

db/migrate/20240826042004_add_style_to_content_items.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddStyleToContentItems < ActiveRecord::Migration[7.1]
+  def change
+    add_column :katalyst_content_items, :style, :json, null: false, default: {}
+  end
+end

spec/dummy/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2023_05_15_151440) do
+ActiveRecord::Schema[7.1].define(version: 2024_08_26_042004) do
   create_table "action_text_rich_texts", force: :cascade do |t|
     t.string "name", null: false
     t.text "body"
@@ -60,6 +60,7 @@
     t.datetime "updated_at", null: false
     t.string "caption"
     t.integer "heading_style", default: 0, null: false
+    t.json "style", default: {}, null: false
     t.index ["container_type", "container_id"], name: "index_katalyst_content_items_on_container"
   end