Active Admin with join table relation - mysql

Question

I am configuring Active Admin. Everything is running apart from a join table, which connects the magazine resource with the keyword resource. One magazine is defined by multiple keywords and a keyword can define multiple magazines.
I have two models:
### models/magazine.rb
class Magazine < ActiveRecord::Base
attr_accessible :colour, :cover_alt, :description, :number, :short, :title_id
has_and_belongs_to_many :keywords, :join_table => "magazines_keywords"
belongs_to :title, :class_name => "Keyword", :foreign_key => "title_id"
end
### models/keywords.rb
class Keyword < ActiveRecord::Base
attr_accessible :word, :description
has_and_belongs_to_many :magazines, :join_table => "magazines_keywords"
end
And a join table:
### models/magazines_keyword.rb
class MagazinesKeyword < ActiveRecord::Base
attr_accessible :magazine_id, :keyword_id
belongs_to :magazine
belongs_to :keyword
end
This setting works for the views of my rails app, and I have the index and show section of my AA magazine resource working, but the form (for new and edit) does not work:
ActiveAdmin.register Magazine do
menu :priority => 1
form do |f|
f.semantic_errors *f.object.errors.keys
f.inputs "Magazine Details" do
f.input :title_id, :label => 'Title', :as => :select, :collection => Keyword.all.map{ |u| ["#{u.word.capitalize}", u.id] }
f.inputs :magazines_keywords do
f.has_many : magazines_keywords do |s|
s.input :keyword, :as => :select, :multiple => true, :collection => MagazinesKeyword.all.map { |u| ["#{u.keyword.word.capitalize}", u.id] }
end
end
end
f.actions
end
show do
panel "Magazine Details" do
attributes_table_for magazine do
row "Keywords", :keyword do |m|
m.keywords.map { |d| d.word }.join(", ").html_safe
end
end
end
active_admin_comments
end
end
When running the app i get NoMethodError in Admin/magazines#edit
Where /active_admin/resource/edit.html.arb line #1 raises undefined method 'klass' for nil:NilClass
I can display all the keywords in the form section with:
f.input :magazines_keywords, :as => :check_boxes, :multiple => true, :collection => MagazinesKeyword.all.map{ |u| ["#{u.keyword.word.capitalize}", u.id] }
But when I try to write them it does not work. Editing the values does not work either.
Where am I missing something? How can I get this working?
****UPDATE****
After some work I got the following solution:
form do |f|
f.semantic_errors *f.object.errors.keys
f.inputs "Saft Details" do
f.input :title_id, :label => 'Title', :as => :select, :collection => Keyword.all.map{ |u| ["#{u.word.capitalize}", u.id] }
f.input :keywords, :as => :check_boxes, :input_html => {:multiple => true}
end
f.actions
end
And as suggested:
f.input :keywords, :as => :check_boxes, :input_html => {:multiple => true} do
f.has_many :keywords do |s|
s.input :keyword, :collection => Keyword.all.map { |kw| ["#{kw.word.capitalize}", kw.id] }
end
end
With both solutions I am able to write a new Magazine entry and get the association written to the join table, unfortunately it displays #<Keyword:0x10c858858> in the form and not the word. What am I missing?

Answer 1

ActiveAdmin is quite smart to understand what you are trying to do. So you should ignore MagazinesKeyword and go straight to Keyword model.
So you should change this:
f.has_many :magazines_keywords do |s|
s.input :keyword, :as => :select, :multiple => true, :collection => MagazinesKeyword.all.map { |u| ["#{u.keyword.word.capitalize}", u.id] }
end
with this:
f.has_many :keywords do |s|
s.input :keyword, :as => :select, :multiple => true, :collection => Keyword.all.map { |kw| ["#{kw.word.capitalize}", kw.id] }
end
Active admin will handle MagazinesKeyword by himself.