module ActsAsTree::ClassMethods

Specify this acts_as extension if you want to model a tree structure by providing a parent association and a children association. This requires that you have a foreign key column, which by default is called parent_id.

class Category < ActiveRecord::Base
  include ActsAsTree

  acts_as_tree :order => "name"
end

Example:
root
 \_ child1
      \_ subchild1
      \_ subchild2

root      = Category.create("name" => "root")
child1    = root.children.create("name" => "child1")
subchild1 = child1.children.create("name" => "subchild1")

root.parent   # => nil
child1.parent # => root
root.children # => [child1]
root.children.first.children.first # => subchild1

In addition to the parent and children associations, the following instance methods are added to the class after calling acts_as_tree:

siblings - Returns all the children of the parent, excluding

the current node (<tt>[subchild2]</tt> when called
on <tt>subchild1</tt>)

self_and_siblings - Returns all the children of the parent,

including the current node (<tt>[subchild1, subchild2]</tt>
when called on <tt>subchild1</tt>)

ancestors - Returns all the ancestors of the current node

(<tt>[child1, root]</tt> when called on <tt>subchild2</tt>)

root - Returns the root of the current node (root
```
when called on <tt>subchild2</tt>)
```

Public Class Methods

generations() click to toggle source

Returns a hash of all nodes grouped by their level in the tree structure.

Class.generations # => { 0=> [root1, root2], 1=> [root1child1, root1child2, root2child1, root2child2] }

# File lib/acts_as_tree.rb, line 131
def self.generations
  all.group_by{ |node| node.tree_level }
end

Public Instance Methods

acts_as_tree(options = {}) click to toggle source

Configuration options are:

primary_key - specifies the column name for relations
```
(default: +id+)
```
foreign_key - specifies the column name to use for tracking
```
of the tree (default: +parent_id+)
```
order - makes it possible to sort the children according to
```
this SQL snippet.
```

counter_cache - keeps a count in a children_count column

if set to +true+ (default: +false+). Specify
a custom column by passing a symbol or string.

# File lib/acts_as_tree.rb, line 66
def acts_as_tree(options = {})
  configuration = {
    primary_key:   "id",
    foreign_key:   "parent_id",
    order:         nil,
    counter_cache: nil,
    dependent:     :destroy,
    touch:         false
  }

  configuration.update(options) if options.is_a?(Hash)

  if configuration[:counter_cache] == true
    configuration[:counter_cache] = :children_count
  end

  belongs_to_opts = {
    class_name:    name,
    primary_key:   configuration[:primary_key],
    foreign_key:   configuration[:foreign_key],
    counter_cache: configuration[:counter_cache],
    touch:         configuration[:touch],
    inverse_of:    :children
  }

  belongs_to_opts[:optional] = true if ActiveRecord::VERSION::MAJOR >= 5

  belongs_to :parent, belongs_to_opts

  if ActiveRecord::VERSION::MAJOR >= 4
    has_many :children, lambda { order configuration[:order] },
      class_name:  name,
      primary_key: configuration[:primary_key],
      foreign_key: configuration[:foreign_key],
      dependent:   configuration[:dependent],
      inverse_of:  :parent
  else
    has_many :children, class_name:  name,
      primary_key: configuration[:primary_key],
      foreign_key: configuration[:foreign_key],
      order:       configuration[:order],
      dependent:   configuration[:dependent],
      inverse_of:  :parent
  end

  class_eval <<-EOV
    include ActsAsTree::InstanceMethods

    def self.default_tree_order
      order_option = %Q{#{configuration.fetch :order, "nil"}}
      order(order_option)
    end

    def self.root
      self.roots.first
    end

    def self.roots
      where(:#{configuration[:foreign_key]} => nil).default_tree_order
    end
  EOV

  # Returns a hash of all nodes grouped by their level in the tree structure.
  #
  # Class.generations # => { 0=> [root1, root2], 1=> [root1child1, root1child2, root2child1, root2child2] }
  def self.generations
    all.group_by{ |node| node.tree_level }
  end


  if configuration[:counter_cache]
    after_update :update_parents_counter_cache

    def children_counter_cache_column
      reflect_on_association(:parent).counter_cache_column
    end

    def leaves
      where(children_counter_cache_column => 0).default_tree_order
    end

  else
    # Fallback to less efficent ways to find leaves.
    class_eval <<-EOV
      def self.leaves
        internal_ids = select(:#{configuration[:foreign_key]}).where(arel_table[:#{configuration[:foreign_key]}].not_eq(nil))
        where("\#{connection.quote_column_name('#{configuration[:primary_key]}')} NOT IN (\#{internal_ids.to_sql})").default_tree_order
      end
    EOV
  end
end

children_counter_cache_column() click to toggle source

# File lib/acts_as_tree.rb, line 139
def children_counter_cache_column
  reflect_on_association(:parent).counter_cache_column
end

leaves() click to toggle source

# File lib/acts_as_tree.rb, line 143
def leaves
  where(children_counter_cache_column => 0).default_tree_order
end