Question

I’m currently working on my first rails project. I am trying to make a web app for uploading pics with friends. So on the form for creating an album, they should have a select field for which friends they want to share the album with. However, I am having trouble showing the names in the select field, and am getting an error

undefined method 'name' for nil:NilClass

even though my user database has the column “name” in it. Am I misunderstanding where “name” comes from? I thought attributes such as @users.name would mean go into the database and find me the name values of each user? Here are my files (let me know if you need any other files):

_form.html.erb (the one with the error)

<%= form_for([@user, @album], :remote => true, :html => { :id => "uploadform", :multipart => true }) do |f| %>
<div>
    <%= f.label :name %>
    <%= f.text_field :name %>


    <%= f.label :description %>
    <%= f.text_area :description %>

    <%= f.select :user, @users.name %>

    <%=f.label :avatar, "Upload" %>
    <%=f.file_field :avatar %>

    <br>

    <%=f.submit %>
</div>
<% end %>

album model

class Album < ActiveRecord::Base
  attr_accessible :avatar, :name
  has_and_belongs_to_many :users

  mount_uploader :avatar, AvatarUploader
end

user model

class User < ActiveRecord::Base

  has_secure_password
  attr_accessible :email, :name, :password, :password_confirmation
  validates_presence_of :password, :on => :create

  validates_format_of :name, :with => /[A-Za-z]+/, :on => :create
  validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i, :on => :create
  validates_length_of :password, :minimum => 5, :on => :create

  has_many :albums
  accepts_nested_attributes_for :albums

end

config/routes

Pholder::Application.routes.draw do
resources :users do
  resources :albums 
end

resources :albums do
  resources :pictures
end

albums controller

class AlbumsController < ApplicationController

    def index
      @albums = Albums.all

      respond_to do |format|
        format.html
        format.json { render json: @albums }
      end
    end

    def show
    end

    def update
    end

    def edit
    end

    def create
      @users = Users.all
      @user = User.find(params[:user_id])
      @album = @user.albums.build(params[:album])
      if @album.save
        flash[:success] = "Album created!"
      end 
    end

    def new
      @user = User.find(params[:user_id])
      @album = Album.new
    end

    def destroy
    end


end

Answer 1

Pay close attention to the error, it can be confusing at first:

undefined method 'name' for nil:NilClass

It says “for nil:NilClass” not “user123:User” That means the object you are calling the #name method on is a nil object not a User object. The error is due to the @user instance variable not being set, so @user is nil instead of an actual user. So I’m guessing params[:user_id] is not being sent properly.