Mongoid monkey patch added
when mongoid is included , dynamic method is added
when you need remove a grid file , you just need to
# xxx is a special field with hash type containing grid_id
after_destroy :remove_xxx
# if xxx is plurals
after_destory :remove_xxx
when you remove a page that contains a field like content that contains some grid fs image
so you need following methods to remove these embed grid file
after_destroy -> {delete_medias :content}
Plug::Mixin
when this module is included, you can use class method
array_attr :x,:y,:z..
# x, y, z a array filed
this method add two method
x_list=(v)
x_list
this two methods convert array field to string between model and view