exclude fallback slide from location slides

The fallback slide should only be retrieved when there is no slides
to be shown.

Author: kevinnio

app/models/spree/slide_location.rb

@@ -1,10 +1,10 @@
 class Spree::SlideLocation < ActiveRecord::Base
-
   has_and_belongs_to_many :slides,
+                          ->(model) { where('spree_slides.id != ?', model.fallback_slide_id || 0) },
                           class_name: 'Spree::Slide',
                           join_table: 'spree_slide_slide_locations'
+
   belongs_to :fallback_slide, class_name: 'Spree::Slide', foreign_key: 'fallback_slide_id'
 
   validates :name, presence: true
-
 end

spec/models/spree/slide_location_spec.rb

@@ -0,0 +1,19 @@
+require 'spec_helper'
+
+RSpec.describe Spree::SlideLocation do
+  let(:slide1) { Spree::Slide.create }
+  let(:slide2) { Spree::Slide.create }
+
+  describe '#slides' do
+    before do
+      Spree::SlideLocation.create name: 'Test location',
+                                  slides: [slide1, slide2],
+                                  fallback_slide: slide1
+    end
+
+    it 'doesnt include its fallback slide' do
+      location = Spree::SlideLocation.find_by! name: 'Test location'
+      expect(location.slides.map(&:id)).to contain_exactly slide2.id
+    end
+  end
+end