[Betternestedset-talk] Retrieving a Subset of the "Tree"

[Larry E. Lutz]

I have a "categories" table, set up as a nested set, that I want to use to
categorize a number of different types of things, such as  books, software,
movies, etc. Since the table is rather large (over 3,000 rows), I would like
to be able to pull subsets of the table for the different types of things. I
can't use a singleton because the same category can apply to more than one
type of thing, and in many cases, a category set for a type of thing may
start a level below the root. In lieu of that, I have several Boolean fields
within the table for the different types of things. The problem is that, no
matter where I try to apply a scope or condition, the system seems to ignore
it and, instead, returns the full dataset.

My schema looks like this:

  create_table "categories", :force => true do |t|
    t.column "parent_id",     :integer
    t.column "lft",           :integer
    t.column "rgt",           :integer
    t.column "topic",         :string,  :default => "",    :null => false
    t.column "description",   :text
    t.column "books",         :boolean, :default => true
    t.column "entities",      :boolean, :default => false
    t.column "movies",        :boolean, :default => false
    t.column "music",         :boolean, :default => false
    t.column "software",      :boolean, :default => false
    t.column "tech_articles", :boolean, :default => false
  end

Within the data in this table, "Movie Genres," for instance, is not a root
level record. Instead, it is buried several layers deep under the
"Performing Arts" root. The identifier for Movie Genres is the Boolean field
"movies."

With set_table_name "categories", here are some of the things that I've
tried that don't work:
------------------------------------------
  has_many :children, :class_name => "MovieGenre", :foreign_key =>
:parent_id, :conditions => "movies = true"
  belongs_to :parent, :class_name => "MovieGenre"
----------------------------------------
  has_many :children, :class_name => "MovieGenre", :foreign_key =>
:parent_id, :conditions => "movies = true"
  belongs_to :parent, :class_name => "MovieGenre", :foreign_key =>
:parent_id, :conditions => "movies = true" 
  acts_as_nested_set :scope => 'movies = true'
  has_many :children, :class_name => "MovieGenre"
  belongs_to :parent, :class_name => "MovieGenre" 
----------------------------------------------

Is there anyway to achieve what I need to accomplish? I really don't want to
go to multiple "categories" tables for each kind of thing because I need to
keep the categories consistent. By the way, I would also like to have a
"long name" returned when I pull the subset, like this:

  def long_name
    self_and_ancestors.map{ |a| a.topic}.join(' > ')
  end

However, that's not absolutely essential. I do need to be able to use the
returned dataset both in a listing and in a select form field.

Any ideas folks?

Larry E. Lutz 
2425 Sage Road, Apt. 53 
Houston, Texas 77056
(713) 850-1358 
lutzle at swbell.net 


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