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Jul 20, 2006, 02:50 #1
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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 explains 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 Development 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")
create table categories ( id int not null auto_increment, name varchar(100) not null, parent_id int, constraint fk_category foreign key (parent_id) references categories(id), primary key (id) );
class Category < ActiveRecord::Base acts_as_tree :order => "name" end
<ul> <% for category in @categories %> <li><%= link_to h(category.title), :action => 'edit', :id => category %> <%= find_all_subcategories(category) %> </li> <% end %> </ul>
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 %>
If you know some tutorial that fully explain how to use acts_as_tree to add and show categories that'll be great.