groups/create, edit, update, destroy 加入 User_id 參數
只有 current_user 跟 作者相同才能在前台顯示 edit / destroy 按鈕
generate migrate add_user_id_to_post
rake db:migrate add_user_id_to_post
posts/create , edit , update, destroy 加入 user_id 機制
只有 current_user 跟 post.user_id 相同才能在前台顯示post => edit / destroy 按鈕
generate migrate create_group_user and model group_user
rake db:migrate create_group_user
setting user and group 多對多資料庫關聯
User 必須是社團成員才能發表文章
generate quit and join group in models/user.rb
generate quit and join in groups_controller
generate quit and join group in models/user.rb
generate quit and join in views/groups/show
User is member of group that create himself
如果不是 group 創辦人，就不會顯示 edit group 按鈕