Fix the nested inheriting about series and snapshot

.rspec_status

@@ -16,3 +16,4 @@ example_id                                 | status | run_time        |
 ./spec/shotengai/models_spec.rb[1:2:1:2]   | passed | 0.3256 seconds  |
 ./spec/shotengai/models_spec.rb[1:2:2:1]   | passed | 0.62601 seconds |
 ./spec/shotengai/models_spec.rb[1:2:2:2]   | passed | 0.45201 seconds |
+./spec/shotengai/models_spec.rb[1:3:1]     | passed | 0.48308 seconds |

lib/shotengai/product.rb

@@ -64,6 +64,13 @@ module Shotengai
     end
 
     class << self
+      def series_class
+        Shotengai::Series
+      end
+
+      def snapshot_class
+        Shotengai::Snapshot
+      end
       # TODO:  ::#{subclass}Series 增加命名规则定义 降低耦合性？？
       def inherited(subclass)
         # 创建相关 series 与 snapshot
@@ -75,8 +82,8 @@ module Shotengai
       def define_related_class subclass
         # Useing Class.new could not get class_name in self.inherited
         class_eval("
-          class ::#{subclass}Series < Shotengai::Series; end;
-          class ::#{subclass}Snapshot < Shotengai::Snapshot; end
+          class ::#{subclass}Series < #{self.series_class}; end;
+          class ::#{subclass}Snapshot < #{self.snapshot_class}; end
         ")
         subclass.instance_eval do
           def series_class;  "#{self.name}Series".constantize ; end

spec/shotengai/models_spec.rb

@@ -266,6 +266,29 @@ RSpec.describe 'Shotengai Models' do
     end
   end
 
+
+  describe 'Nested Inherited' do
+    before do
+      class Good < Shotengai::Product; end
+      class NestedGood < Good; end
+      class GoodSeries
+        def a
+          'outside a'
+        end
+      end
+      class NestedGoodSeries < GoodSeries
+        def a
+          'nested a'
+        end
+      end
+    end
+
+    it 'does something' do
+      expect(GoodSeries.new.a).to eq('outside a')
+      expect(NestedGoodSeries.new.a).to eq('nested a')
+    end
+  end
+
   after do
     ActiveRecord::Migration[5.1].subclasses.each do |migrate|
       migrate.migrate(:down)
@@ -273,6 +296,3 @@ RSpec.describe 'Shotengai Models' do
   end
 end
 
-# ActiveRecord::Migration[5.1].subclasses.each do |migrate|
-#   migrate.migrate(:down)
-# end
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