dynamically define an update validator

lib/stateful_enum/machine.rb

@@ -57,7 +57,7 @@ def initialize(model, column, states, prefix, suffix, name, &block)
             if to && (condition.nil? || instance_exec(&condition))
               #TODO transaction?
               run_callbacks value_method_name do
-                original_method = self.class.send(:_enum_methods_module).instance_method "#{prefix}#{to}#{suffix}!"
+                original_method = self.base_class.send(:_enum_methods_module).instance_method "#{prefix}#{to}#{suffix}!"
                 original_method.bind(self).call
               end
             else
@@ -85,6 +85,18 @@ def initialize(model, column, states, prefix, suffix, name, &block)
           define_method "#{value_method_name}_transition" do
             transitions[send(column).to_sym].try! :first
           end
+
+          validate on: :update do
+            state_from, state_to = changes[column]
+            next if state_from.nil? || state_to.nil?
+            state_from = state_from.to_sym; state_to = state_to.to_sym
+
+            all_possible_transitions = model.instance_variable_get(:@_defined_stateful_enums).flat_map {|enum| enum.events.map(&:transitions) }
+            filtered_transitions = all_possible_transitions.map! {|h| h[state_from] }.compact
+            unless filtered_transitions.any? {|to, _condition| to == state_to }
+              errors.add column, "cannot transition from #{state_from} to #{state_to}"
+            end
+          end
         end
       end
 

test/dummy/app/models/special_bug.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class SpecialBug < Bug
+end

test/dummy/db/migrate/20160307203948_create_bugs.rb

@@ -8,6 +8,7 @@ def change
       t.integer :status, default: 0
       t.integer :assigned_to_id
       t.datetime :resolved_at
+      t.string :type
 
       t.timestamps null: false
     end

test/mechanic_machine_test.rb

@@ -10,6 +10,14 @@ def test_transition
     bug.assign
     assert_equal 'assigned', bug.status
   end
+
+  def test_transition_to_sti
+    special_bug = SpecialBug.new
+    assert_equal 'unassigned', special_bug.status
+    special_bug.assigned_to = User.create!(name: 'user 1')
+    special_bug.assign
+    assert_equal 'assigned', special_bug.status
+  end
 
   def test_transition!
     bug = Bug.new
@@ -51,6 +59,17 @@ def test_invalid_transition!
     assert_equal 'resolved', bug.status
   end
 
+  def test_validation_with_direct_attribute_write
+    bug = Bug.new
+    bug.status = 'resolved'
+    assert_equal true, bug.valid?
+    bug.save!
+    assert_equal 'resolved', bug.status
+
+    bug.status = 'assigned'
+    assert_equal false, bug.valid?
+  end
+
   def test_can_xxxx?
     bug = Bug.new
     assert bug.can_resolve?
@@ -251,5 +270,20 @@ def test_enum_definition_with_prefix_and_suffix
       tes.prefix_archive_suffix
       assert_equal 'archived', tes.status
     end
+
+    def test_validation_with_direct_attribute_write_with_prefix_and_suffix
+      ActiveRecord::Migration.create_table(:attribute_write_with_prefix_and_suffix_test) { |t| t.integer :status }
+      t = Class.new(ActiveRecord::Base) do
+        self.table_name = 'attribute_write_with_prefix_and_suffix_test'
+        enum(:status, [:active, :archived], prefix: :prefix, suffix: :suffix) { event(:archive) { transition(active: :archived) } }
+      end.new status: :active
+      t.status = 'archived'
+      assert_equal true, t.valid?
+      t.save!
+      assert_equal 'archived', t.status
+
+      t.status = 'active'
+      assert_equal false, t.valid?
+    end
   end
 end