I’m trying to create categories that have their own subcategories, and
each subcategory may have its own subcategories, … and so on.
After some reading, I found out that the best way for creating such a
thing is to use acts_as_tree, but I didn’t find any tutorial or article
that explain this in a clear way. After a lot of work I was finally
able to create categories and subcategories using the following code
explained in (Agile Web D. With Rails) book:
root = Category.create(:name => “Books”)
fiction = root.children.create(:name => “Fiction”)
non_fiction = root.children.create(:name => “Non Fiction”)
non_fiction.children.create(:name => “Computers”)
non_fiction.children.create(:name => “Science”)
non_fiction.children.create(:name => “Art History”)
fiction.children.create(:name => “Mystery”)
fiction.children.create(:name => “Romance”)
fiction.children.create(:name => “Science Fiction”)
And here is the database scheme:
create table categories (
id int not null auto_increment,
name varchar(100) not null,
constraint fk_category foreign key (parent_id) references
primary key (id)
in the model:
class Category < ActiveRecord::Base
acts_as_tree :order => “name”
OK, my problem now is how to view something! Any category name, or any
subcategory or a list of categories, I tried a lot of things, like (in
<% for category in @categories %>
- <%= link_to h(category.title), :action => 'edit', :id => category %> <%= find_all_subcategories(category) %> <% end %>
But I ALWAYS and whatever I try I got this error message:
"You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occured while evaluating nil.each
Extracted source (around line #2): <% for category in @categories %> "
What do you think the problem is?
If you know some tutorial that fully explain how to use acts_as_tree to
add and show categories that’ll be great