ruby on rails 4 mass assignment -

i have:

• a model user common data such email, password, first_name, last_name
• a model student specific data such faculty_id, etc..

what want have possibility modify student's profile, e.g change faculty , credentials. found out accepts_nested_attributes_for should me that. have:

class user < activerecord::base   has_one :student  has_one :header  has_one :admin  has_many :progresses, :through => :student   accepts_nested_attributes_for :student  end  class student < activerecord::base    belongs_to :user   belongs_to :group   has_one :specialization, through: :group   has_many :progresses   scope :activated, lambda {(where("users.activated = 'off'"))}   self.per_page = 1  end  class admin::studentscontroller < admincontroller   before_action :set_user, only: [:show, :edit, :update, :destroy]    def index     @students = student.joins(:user).joins(:group).paginate(:page => params[:page]).all   end    def show   end    def edit   end    def update   end    private    def set_user     @student = student.find(params[:id])     @student.build_user    end end 

form partial

= form_for([:admin,@student]) |f|  - if @student.errors.any?   #error_explanation    h2     = pluralize(@student.errors.count, "error")     | prohibited group being saved:    ul     - @student.errors.full_messages.each |msg|       li= msg   .field    = f.fields_for :user |builder|    = builder.label :first_name   br/    = builder.text_field :first_name   .field   = f.label :faculty_id   br/   = f.text_field :faculty_id .actions = f.submit 

i looked inspect element in browser , input user object

<input id="student_user_first_name" name="student[user][first_name]" type="text"> 

which seems correct. field empty. please tell me went wrong? thank you.

rails 4 uses strong parameters, need whitelist params in controller. here explanation considers use of accepts_nested_attribute_for. http://edgeapi.rubyonrails.org/classes/actioncontroller/strongparameters.html