Creating a many-to-many via params and accepts_nested_attributes

business.rb

class Business < ActiveRecord::Base
  has_many   :businesses_users, :primary_key=>:business_id
  has_many   :users, through: :businesses_users
end

nested_many_to_many.rb

#NO:
params = {"business"=>{"user_id"=>"1", "name"=>"my business name"}}

#NO:
params = {"business"=>{"users"=>{"id"=>"1"}, "name"=>"my business name"}}

#NO:
params = {"business"=>{"businesses_users"=>{"user_id"=>"1", "business_id"=>"1"}, "name"=>"my business name"}}

#NO:
params = {"business"=>{"businesses_users_attributes"=>{"user_id"=>"1", "business_id"=>"1"}, "name"=>"my business name"}}

#YES:
params = {"business"=>{"businesses_users_attributes"=>{"0"=>{"user_id"=>"1", "business_id"=>"1"}}, "name"=>"my business name"}}

business = Business.new(params)