Migrate TaxRate, TaxCategory relation to a M-M

Implements solidusio#1836

The current relation between TaxRate and TaxCategory can lead
to unnecessary tax rates if a store has multiple tax categories
and if it supports countries (such as Australia) that have a
standard tax rate. This means that for each TaxCategory, the store
will have an extra tax rate even if the percent is the same.

By transforming this relation to a M-M we can allow stores to
create tax rates that have multiple tax categories.

backend/app/views/spree/admin/tax_rates/_form.html.erb

@@ -25,8 +25,8 @@
  <%= f.collection_select(:zone_id, @available_zones, :id, :name, {}, {class: 'select2 fullwidth'}) %>
  </div>
  <div data-hook="category" class="field">
- <%= f.label :tax_category_id, Spree::TaxCategory.model_name.human %>
- <%= f.collection_select(:tax_category_id, @available_categories,:id, :name, {}, {class: 'select2 fullwidth'}) %>
+ <%= f.label :tax_category_ids, Spree::TaxCategory.model_name.human %>
+ <%= f.collection_select(:tax_category_ids, @available_categories, :id, :name, {}, {class: 'select2 fullwidth', multiple: "multiple"}) %>
  </div>
  <div data-hook="show_rate" class="field">
  <%= f.check_box :show_rate_in_label %>

backend/app/views/spree/admin/tax_rates/index.html.erb

@@ -29,7 +29,7 @@
  <tr data-hook="rate_header">
  <th><%= Spree::TaxRate.human_attribute_name(:zone) %></th>
  <th><%= Spree::TaxRate.human_attribute_name(:name) %></th>
- <th><%= Spree::TaxRate.human_attribute_name(:tax_category_id) %></th>
+ <th><%= Spree::TaxRate.human_attribute_name(:tax_categories) %></th>
  <th><%= Spree::TaxRate.human_attribute_name(:amount) %></th>
  <th><%= Spree::TaxRate.human_attribute_name(:included_in_price) %></th>
  <th><%= Spree::TaxRate.human_attribute_name(:show_rate_in_label) %></th>
@@ -42,7 +42,13 @@
  <tr id="<%= spree_dom_id tax_rate %>" data-hook="rate_row" class="<%= cycle('odd', 'even')%>">
  <td class="align-center"><%=tax_rate.zone.try(:name) || Spree.t(:not_available) %></td>
  <td class="align-center"><%=tax_rate.name %></td>
- <td class="align-center"><%=tax_rate.tax_category.try(:name) || Spree.t(:not_available) %></td>
+ <td class="align-center">
+ <% if tax_rate.tax_categories.any? %>
+ <%= tax_rate.tax_categories.map(&:name).join(", ") %>
+ <% else %>
+ <%= Spree.t(:not_available) %>
+ <% end %>
+ </td>
  <td class="align-center"><%=tax_rate.amount %></td>
  <td class="align-center"><%=tax_rate.included_in_price? ? Spree.t(:say_yes) : Spree.t(:say_no) %></td>
  <td class="align-center"><%=tax_rate.show_rate_in_label? ? Spree.t(:say_yes) : Spree.t(:say_no) %></td>

backend/spec/features/admin/configuration/tax_rates_spec.rb

@@ -12,7 +12,7 @@
 
  # Regression test for https://github.com/spree/spree/issues/535
  it "can see a tax rate in the list if the tax category has been deleted" do
- tax_rate.tax_category.update_column(:deleted_at, Time.current)
+ tax_rate.tax_categories.first.update_column(:deleted_at, Time.current)
  click_link "Tax Rates"
 
  expect(find("table tbody td:nth-child(3)")).to have_content('N/A')

backend/spec/features/admin/orders/adjustments_spec.rb

@@ -5,7 +5,7 @@
 
  let!(:ship_address) { create(:address) }
  let!(:tax_zone) { create(:global_zone) } # will include the above address
- let!(:tax_rate) { create(:tax_rate, amount: 0.20, zone: tax_zone, tax_category: tax_category) }
+ let!(:tax_rate) { create(:tax_rate, amount: 0.20, zone: tax_zone, tax_categories: [tax_category]) }
 
  let!(:order) do
  create(

core/app/models/spree/calculator/default_tax.rb

@@ -9,7 +9,7 @@ class Calculator::DefaultTax < Calculator
  # Orders created with Spree 2.2 and after, have them applied to the line items individually.
  def compute_order(order)
  matched_line_items = order.line_items.select do |line_item|
- line_item.tax_category == rate.tax_category
+ rate.tax_categories.include?(line_item.tax_category)
  end
 
  line_items_total = matched_line_items.sum(&:discounted_amount)

core/app/models/spree/tax/shipping_rate_taxer.rb

@@ -23,7 +23,7 @@ def tax(shipping_rate)
 
  def tax_rates_for_shipping_rate(shipping_rate)
  applicable_rates(shipping_rate.order).select do |tax_rate|
- tax_rate.tax_category == shipping_rate.tax_category
+ tax_rate.tax_categories.include?(shipping_rate.tax_category)
  end
  end
  end

core/app/models/spree/tax/tax_helpers.rb

@@ -17,9 +17,9 @@ module TaxHelpers
  #
  # For further discussion, see https://github.com/spree/spree/issues/4397 and https://github.com/spree/spree/issues/4327.
  def applicable_rates(order)
- order_zone_tax_category_ids = rates_for_order(order).map(&:tax_category_id)
+ order_zone_tax_category_ids = rates_for_order(order).flat_map(&:tax_categories).map(&:id)
  default_rates_with_unmatched_tax_category = rates_for_default_zone.to_a.delete_if do |default_rate|
- order_zone_tax_category_ids.include?(default_rate.tax_category_id)
+ (order_zone_tax_category_ids & default_rate.tax_categories.map(&:id)).any?
  end
 
  (rates_for_order(order) + default_rates_with_unmatched_tax_category).uniq
@@ -38,7 +38,9 @@ def sum_of_included_tax_rates(item)
  end
 
  def rates_for_item(item)
- applicable_rates(item.order).select { |rate| rate.tax_category_id == item.tax_category_id }
+ applicable_rates(item.order).select do |rate|
+ rate.tax_categories.map(&:id).include?(item.tax_category_id)
+ end
  end
  end
  end

core/app/models/spree/tax_category.rb

@@ -4,7 +4,15 @@ class TaxCategory < Spree::Base
  validates :name, presence: true
  validates_uniqueness_of :name, unless: :deleted_at
 
- has_many :tax_rates, dependent: :destroy, inverse_of: :tax_category
+ has_many :tax_rate_tax_categories,
+ class_name: Spree::TaxRateTaxCategory,
+ dependent: :destroy,
+ inverse_of: :tax_category
+ has_many :tax_rates,
+ through: :tax_rate_tax_categories,
+ class_name: Spree::TaxRate,
+ inverse_of: :tax_categories
+
  after_save :ensure_one_default
 
  def self.default

core/app/models/spree/tax_rate.rb

@@ -9,13 +9,20 @@ class TaxRate < Spree::Base
  include Spree::AdjustmentSource
 
  belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates
- belongs_to :tax_category, class_name: "Spree::TaxCategory", inverse_of: :tax_rates
+
+ has_many :tax_rate_tax_categories,
+ class_name: Spree::TaxRateTaxCategory,
+ dependent: :destroy,
+ inverse_of: :tax_rate
+ has_many :tax_categories,
+ through: :tax_rate_tax_categories,
+ class_name: Spree::TaxCategory,
+ inverse_of: :tax_rates
 
  has_many :adjustments, as: :source
  has_many :shipping_rate_taxes, class_name: "Spree::ShippingRateTax"
 
  validates :amount, presence: true, numericality: true
- validates :tax_category_id, presence: true
 
  # Finds all tax rates whose zones match a given address
  scope :for_address, ->(address) { joins(:zone).merge(Spree::Zone.for_address(address)) }
@@ -94,10 +101,12 @@ def compute_amount(item)
  private
 
  def adjustment_label(amount)
- Spree.t translation_key(amount),
- scope: "adjustment_labels.tax_rates",
- name: name.presence || tax_category.name,
- amount: amount_for_adjustment_label
+ Spree.t(
+ translation_key(amount),
+ scope: "adjustment_labels.tax_rates",
+ name: name.presence || tax_categories.map(&:name).join(", "),
+ amount: amount_for_adjustment_label
+ )
  end
 
  def amount_for_adjustment_label

core/app/models/spree/tax_rate_tax_category.rb

@@ -0,0 +1,6 @@
+module Spree
+ class TaxRateTaxCategory < Spree::Base
+ belongs_to :tax_rate, class_name: Spree::TaxRate, inverse_of: :tax_rate_tax_categories
+ belongs_to :tax_category, class_name: Spree::TaxCategory, inverse_of: :tax_rate_tax_categories
+ end
+end

core/db/migrate/20170412103617_transform_tax_rate_category_relation.rb

@@ -0,0 +1,48 @@
+class TransformTaxRateCategoryRelation < ActiveRecord::Migration[5.0]
+ class TaxRate < ActiveRecord::Base
+ self.table_name = "spree_tax_rates"
+ end
+
+ class TaxRateTaxCategory < ActiveRecord::Base
+ self.table_name = "spree_tax_rate_tax_categories"
+ end
+
+ def up
+ create_table :spree_tax_rate_tax_categories do |t|
+ t.integer :tax_category_id, index: true, null: false
+ t.integer :tax_rate_id, index: true, null: false
+ end
+
+ add_foreign_key :spree_tax_rate_tax_categories, :spree_tax_categories, column: :tax_category_id
+ add_foreign_key :spree_tax_rate_tax_categories, :spree_tax_rates, column: :tax_rate_id
+
+ TaxRate.where.not(tax_category_id: nil).find_each do |tax_rate|
+ TaxRateTaxCategory.create!(
+ tax_rate_id: tax_rate.id,
+ tax_category_id: tax_rate.tax_category_id
+ )
+ end
+
+ remove_column :spree_tax_rates, :tax_category_id
+ end
+
+ def down
+ add_column :spree_tax_rates, :tax_category_id, :integer, index: true
+ add_foreign_key :spree_tax_rates, :spree_tax_categories, column: :tax_category_id
+
+ TaxRate.find_each do |tax_rate|
+ tax_category_ids = TaxRateTaxCategory.where(tax_rate_id: tax_rate.id).pluck(:tax_category_id)
+
+ tax_category_ids.each_with_index do |category_id, i|
+ if i.zero?
+ tax_rate.update!(tax_category_id: category_id)
+ else
+ new_tax_rate = tax_rate.dup
+ new_tax_rate.update!(tax_category_id: category_id)
+ end
+ end
+ end
+
+ drop_table :spree_tax_rate_tax_categories
+ end
+end

core/lib/spree/testing_support/factories/adjustment_factory.rb

@@ -29,7 +29,11 @@
  after(:create) do |adjustment|
  # Set correct tax category, so that adjustment amount is not 0
  if adjustment.adjustable.is_a?(Spree::LineItem)
- adjustment.source.tax_category = adjustment.adjustable.tax_category
+ if adjustment.adjustable.tax_category.present?
+ adjustment.source.tax_categories = [adjustment.adjustable.tax_category]
+ else
+ adjustment.source.tax_categories = []
+ end
  adjustment.source.save
  adjustment.update!
  end

core/lib/spree/testing_support/factories/tax_rate_factory.rb

@@ -6,7 +6,7 @@
  factory :tax_rate, class: Spree::TaxRate do
  zone
  amount 0.1
- tax_category
  association(:calculator, factory: :default_tax_calculator)
+ tax_categories { [build(:tax_category)] }
  end
 end

sample/db/samples/tax_rates.rb

@@ -3,7 +3,11 @@
 tax_rate = Spree::TaxRate.create(
  name: "North America",
  zone: north_america,
- amount: 0.05,
- tax_category: clothing)
+ amount: 0.05
+)
 tax_rate.calculator = Spree::Calculator::DefaultTax.create!
 tax_rate.save!
+Spree::TaxRateTaxCategory.create!(
+ tax_rate: tax_rate,
+ tax_category: clothing
+)