Add a EssenceSpreeVariant essence

app/models/alchemy/essence_spree_variant.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module Alchemy
+  class EssenceSpreeVariant < ActiveRecord::Base
+    VARIANT_ID = /\A\d+\z/
+
+    belongs_to :variant, class_name: 'Spree::Variant', optional: true
+
+    acts_as_essence(
+      ingredient_column: :variant,
+      preview_text_method: :name
+    )
+
+    def ingredient=(variant)
+      case variant
+      when VARIANT_ID
+        self.variant = Spree::Variant.new(id: variant)
+      when Spree::Variant
+        self.variant = variant
+      else
+        super
+      end
+    end
+  end
+end

app/views/alchemy/essences/_essence_spree_variant_editor.html.erb

@@ -0,0 +1,9 @@
+<div class="content_editor essence_spree_variant" id="<%= content.dom_id %>" data-content-id="<%= content.id %>">
+  <%= content_label(content) %>
+  <%= select_tag(
+    content.form_field_name,
+    options_from_collection_for_select(Spree::Variant.all, :id, :name, content.essence.variant_id),
+    id: content.form_field_id,
+    class: 'alchemy_selectbox full_width'
+  ) %>
+</div>

db/migrate/20191107135822_create_alchemy_essence_spree_variants.rb

@@ -0,0 +1,9 @@
+class CreateAlchemyEssenceSpreeVariants < ActiveRecord::Migration[5.2]
+  def change
+    create_table :alchemy_essence_spree_variants do |t|
+      t.references :variant, null: true, foreign_key: { to_table: Spree::Variant.table_name }
+
+      t.timestamps
+    end
+  end
+end

spec/models/alchemy/essence_spree_variant_spec.rb

@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+require 'alchemy/test_support/essence_shared_examples'
+require 'alchemy/test_support/factories/page_factory'
+require 'alchemy/test_support/factories/element_factory'
+require 'alchemy/test_support/factories/content_factory'
+require 'spree/testing_support/factories/variant_factory'
+
+require_dependency 'alchemy/site'
+
+RSpec.describe Alchemy::EssenceSpreeVariant, type: :model do
+  let(:variant) { build(:variant) }
+  let(:essence) { described_class.new(variant: variant) }
+
+  it_behaves_like 'an essence' do
+    let(:ingredient_value) { variant }
+  end
+
+  describe 'ingredient=' do
+    subject(:ingredient) { essence.variant }
+
+    context 'when String value is only a number' do
+      let(:value) { '101' }
+
+      before do
+        essence.ingredient = value
+      end
+
+      it 'sets variant to an variant instance with that id' do
+        is_expected.to be_a(Spree::Variant)
+        expect(ingredient.id).to eq(101)
+      end
+    end
+
+    context 'when value is an Spree Variant' do
+      let(:value) { variant }
+
+      before do
+        essence.ingredient = value
+      end
+
+      it 'sets variant to an variant instance with that id' do
+        is_expected.to be_a(Spree::Variant)
+        expect(ingredient).to eq(variant)
+      end
+    end
+
+    context 'when value is not only a number' do
+      let(:value) { 'variant1' }
+
+      it do
+        expect {
+          essence.ingredient = value
+        }.to raise_error(ActiveRecord::AssociationTypeMismatch)
+      end
+    end
+  end
+end

spec/views/alchemy/essences/essence_spree_variant_editor_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'alchemy/essences/_essence_spree_variant_editor' do
+  let(:content) { Alchemy::Content.new(essence: essence) }
+  let(:essence) { Alchemy::EssenceSpreeVariant.new }
+
+  before do
+    view.class.send(:include, Alchemy::Admin::EssencesHelper)
+    allow(view).to receive(:content_label).and_return(content.name)
+  end
+
+  it "renders a variant select box" do
+    render 'alchemy/essences/essence_spree_variant_editor', content: content
+    expect(rendered).to have_css('select.alchemy_selectbox.full_width')
+  end
+
+  context 'with a variant related to essence' do
+    let(:product) { Spree::Product.new(name: 'Chocolate') }
+    let(:variant) { Spree::Variant.new(id: 1, product: product) }
+    let(:essence) { Alchemy::EssenceSpreeVariant.new(variant_id: variant.id) }
+
+    before do
+      expect(Spree::Variant).to receive(:all) { [variant] }
+    end
+
+    it "selects variant in select box" do
+      render 'alchemy/essences/essence_spree_variant_editor', content: content
+      expect(rendered).to have_css('option[value="1"][selected]')
+    end
+  end
+end