fixes for form

app/models/book.rb

@@ -31,6 +31,8 @@ class Book
   has_and_belongs_to_many :book_authors
   accepts_nested_attributes_for :book_authors
 
+  has_and_belongs_to_many :book_author_types
+
   belongs_to :book_type
   before_validation :add_http
 

app/models/book_author_type.rb

@@ -7,5 +7,6 @@ class BookAuthorType
   field :key, type: String
   field :title, type: String, localize: true
   	
+  has_and_belongs_to_many :books
   has_and_belongs_to_many :book_authors
 end

app/views/admin/books/_form.html.erb

@@ -43,7 +43,6 @@
 				<%= content_tag :label,:class => "checkbox inline" do -%>
 					<%= check_box_tag 'book[book_author_type_ids][]', author_type.id, @book.book_author_type_ids.include?(author_type.id)%>
 					<%= author_type.title %>
-	    			<%= hidden_field_tag 'book[book_author_type_ids][]', '' %>
 				<% end %>
 			<% end %>
         </div>