Add SemanticLink model for variants

We want to link variants/products to external DFC SuppliedProducts to
trigger supplier orders when local stock is exhausted. This is the first
step to enable the link.

app/models/semantic_link.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+# Link a Spree::Variant to an external DFC SuppliedProduct.
+class SemanticLink < ApplicationRecord
+  belongs_to :variant, class_name: "Spree::Variant"
+
+  validates :semantic_id, presence: true
+end

app/models/spree/variant.rb

@@ -56,6 +56,7 @@ module Spree
     has_many :exchanges, through: :exchange_variants
     has_many :variant_overrides, dependent: :destroy
     has_many :inventory_items, dependent: :destroy
+    has_many :semantic_links, dependent: :delete_all
 
     localize_number :price, :weight
 

db/migrate/20240105043228_create_semantic_links.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class CreateSemanticLinks < ActiveRecord::Migration[7.0]
+  def change
+    create_table :semantic_links do |t|
+      t.references :variant, null: false, foreign_key: { to_table: :spree_variants }
+      t.string :semantic_id, null: false
+
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -400,6 +400,14 @@ ActiveRecord::Schema[7.0].define(version: 2024_02_13_044159) do
     t.datetime "updated_at", precision: nil, null: false
   end
 
+  create_table "semantic_links", force: :cascade do |t|
+    t.bigint "variant_id", null: false
+    t.string "semantic_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["variant_id"], name: "index_semantic_links_on_variant_id"
+  end
+
   create_table "sessions", id: :serial, force: :cascade do |t|
     t.string "session_id", limit: 255, null: false
     t.text "data"
@@ -1168,6 +1176,7 @@ ActiveRecord::Schema[7.0].define(version: 2024_02_13_044159) do
   add_foreign_key "proxy_orders", "spree_orders", column: "order_id", name: "order_id_fk"
   add_foreign_key "proxy_orders", "subscriptions", name: "proxy_orders_subscription_id_fk"
   add_foreign_key "report_rendering_options", "spree_users", column: "user_id"
+  add_foreign_key "semantic_links", "spree_variants", column: "variant_id"
   add_foreign_key "spree_addresses", "spree_countries", column: "country_id", name: "spree_addresses_country_id_fk"
   add_foreign_key "spree_addresses", "spree_states", column: "state_id", name: "spree_addresses_state_id_fk"
   add_foreign_key "spree_inventory_units", "spree_orders", column: "order_id", name: "spree_inventory_units_order_id_fk", on_delete: :cascade

spec/models/semantic_link_spec.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe SemanticLink, type: :model do
+  it { is_expected.to belong_to :variant }
+  it { is_expected.to validate_presence_of(:semantic_id) }
+end

spec/models/spree/variant_spec.rb

@@ -6,6 +6,8 @@ require 'spree/localized_number'
 describe Spree::Variant do
   subject(:variant) { build(:variant) }
 
+  it { is_expected.to have_many :semantic_links }
+
   context "validations" do
     it "should validate price is greater than 0" do
       variant.price = -1