CODEWITHSUNDEEP
ruby-on-rails
Hussain Akhtar Wahid 'Ghouri'
Hussain Akhtar Wahid 'Ghouri'

Reputation: 6617

undefined method `map' for nil:NilClass , what causes this?

Hi i am facing this error , completely new to rails so cant figure out what is causing it

my newBook.html.erb

<html>
    <head>
        <title> new Book </title>
    </head>
    <body>
        <h1><%= @hello_message %></h1>
        <h1>Add new book</h1>
        <%= form_tag :action => 'create' %>
        <p>
            <label for="book_title">Title</label>:
            <%= text_field 'book', 'title' %>
        </p>
        <p>
            <label for="book_price">Price</label>:
            <%= text_field 'book', 'price' %>
        </p>
        <p>
            <label for="book_subject">Subject</label>:
            <%= collection_select(:book,:subject_id,@subjects,:id,:name) %>
        </p>
        <p>
            <label for="book_description">Description</label>
            <br/>
            <%= text_area 'book', 'description' %>
        </p>
        <%= submit_tag "Create" %>
        <%= end_form_tag %>
        <%= link_to 'Back', {:action => 'list'} %>
    </body>
</html>

my book model : book.rb

class Book < ActiveRecord::Base
  attr_accessible :title, :price,:description , :created_at 
  belongs_to :subject
  validates_presence_of :title
  validates_numericality_of :price, :message=>"Error Message"
end

my subject model : subject.rb

class Subject < ActiveRecord::Base
  attr_accessible :name
  has_many :book

end

stack trace is :

actionpack (3.2.13) lib/action_view/helpers/form_options_helper.rb:364:in `options_from_collection_for_select'
actionpack (3.2.13) lib/action_view/helpers/form_options_helper.rb:600:in `to_collection_select_tag'
actionpack (3.2.13) lib/action_view/helpers/form_options_helper.rb:191:in `collection_select'
app/views/home/newBook.html.erb:19:in `_app_views_home_new_ook_html_erb__299261930_24178164'
actionpack (3.2.13) lib/action_view/template.rb:145:in `block in render'
activesupport (3.2.13) lib/active_support/notifications.rb:125:in `instrument'
actionpack (3.2.13) lib/action_view/template.rb:143:in `render'
# -- snipped --

Upvotes: 7

Views: 36443

Answers (4)

JayantSeth
JayantSeth

Reputation: 408

I recently ran into this issue. I had defined the object for the new method (which called the form page using GET) but had forgotten to define it for the create method (which accepted form values using POST), after defining it for both the new and the create issue got resolved.

Upvotes: 0

TattooedJoey
TattooedJoey

Reputation: 93

For people looking at this post and the answer isn't working for them;

I was trying to link the table "Locations" in the table "Departments".

The following code worked for me, having taking inspiration from the original answer;

# In app/views/departments/_form.html.erb:
...
    <p>
        <%= f.label :location %><br>
        <%= f.collection_select(:location,@locations,:id,:address) %>
    </p>    
...

# In app/controllers/departments_controller.rb;

  def new
    @locations = Location.all
  ....
  end

Upvotes: 0

Deepika
Deepika

Reputation: 826

<%= collection_select(:book,:subject_id,Subject.all,:id,:name) %>

Upvotes: 2

Matt
Matt

Reputation: 14048

<%= collection_select(:book,:subject_id,@subjects,:id,:name) %>

Your @subjects object is undefined. You need in your controller action for this page something that sets the contents of that variable, for example:

@subjects = Subject.all

See the source for options_from_collection_for_select - first thing it does is a map call on the collection passed to it (in your case @subjects).

Upvotes: 23

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