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Turn an acts_as_tree structure into a select drop-down.

Published by Rabbit on February 1, 2008 06:09 pm under Rails

This is probably the easiest way to turn Rails’ acts_as_tree structure into a select field:

HTML:

<select name="category_id">
  <%= expand_tree_into_select_field(Category.top) %>
</select>

Ruby helper:

def expand_tree_into_select_field(categories)
  returning(String.new) do |html|
    categories.each do |category|
      html << %{<option value="#{ category.id }">#{ '&nbsp;&nbsp;&nbsp;' * category.ancestors.size }#{ category.name }</option>}
      html << expand_tree_into_select_field(category.children) if category.has_children?
    end
  end
end

The Category.top method is simply:

def self.top
  find(:all, :conditions => [ 'parent_id IS NULL' ])
end

Finally, your Category class should implement has_children?:

def has_children?
  children.size > 0
end

That last bit is, of course, optional. You could easily write category.children.size > 0, but that’s not very object-oriented now, is it?

Enjoy!

2 Comments so far

Marquis on February 11th, 2008

Did something similar but with checkboxes the other day. Three things: 1) returning - Cool new tool, Ive been looking for something like this.
2) find(:all, :conditions => [ ‘parent_id IS NULL’ ]) - how about find_all_by_parent_id(NULL) ??
3) option_groups_from_collection_for_select ??
Rabbit on February 12th, 2008

Model.find_all_by_parent_id(nil) works, too. Oddly enough I believe I did use that format elsewhere in the program.

Something like this could definitely be turned into a plugin or generic helper method, especially with a block to determine output.

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Turn an acts_as_tree structure into a select drop-down.

2 Comments so far

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