after_destroy フック

destroy アクション内で例外を捕捉

depot/app/controllers/users_controller.rb

@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 class UsersController < ApplicationController
   # GET /users
   # GET /users.xml
@@ -75,7 +76,12 @@ def update
   # DELETE /users/1.xml
   def destroy
     @user = User.find(params[:id])
-    @user.destroy
+      begin
+          flash[:notice] = "ユーザ #{@user.name} は削除されました"
+          @user.destroy
+      rescue Exception => e
+          flash[:notice] = e.message
+      end
 
     respond_to do |format|
       format.html { redirect_to(users_url) }

depot/app/models/user.rb

@@ -35,6 +35,12 @@ def self.authenticate (name, password)
         user
     end
 
+    def after_destroy
+        if User.count.zero?
+            raise "最後のユーザは削除できません"
+        end
+    end
+
     private
 
     def password_non_blank