Belongs_to only recognized by console, not server - ruby-on-rails

Question

I've got a really weird problem with my project. I've got 2 models, the one is Link and the other Category. I've got a index view where all the links should be listed, together with the corresponding category names. When running the server and trying to use
<%= link.category.name %>
I get an error page with the following:
undefined method `name' for nil:NilClass
But when I open the console and write:
link = Link.find(1) #there is currently only one link
link.category.name
It returns the correct category name.
Here are my Models and schema.rb:
class Link < ActiveRecord::Base
attr_accessible :category_id, :description, :title, :url, :visible
belongs_to :category
scope :visible, lambda { where(visible: true) }
end
.
class Category < ActiveRecord::Base
attr_accessible :name
has_many :links
end
.
ActiveRecord::Schema.define(:version => 20130420070717) do
create_table "categories", :force => true do |t|
t.string "name"
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
end
add_index "categories", ["id"], :name => "index_categories_on_id"
create_table "links", :force => true do |t|
t.string "title"
t.text "description"
t.string "url"
t.integer "category_id"
t.boolean "visible"
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
end
add_index "links", ["category_id"], :name => "index_links_on_category_id"
add_index "links", ["id"], :name => "index_links_on_id"
end
How can this happen? Thank you very much for your help!

Answer 1

Maybe I can help others facing the same issue.
The category_id was assigned to the link by a form which queries the existing categories from the db.
<%= f.select(:category_id, #categories.collect { |c| c.name }) %>
The category I wanted to assign has the id = 1. After selecting the category from the dropdown menu, the link.category_id was 0, it should have been 1.
UPDATE:
I fixed the wrong index by:
<%= f.collection_select :category_id, #categories, :id, :name, :prompt => "Select a category" %>