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module ActiveRecord
module Acts #:nodoc:
module NestedSet #:nodoc:
def self.included(base)
base.extend(ClassMethods)
end
# This +acts_as+ extension provides Nested Set functionality. Nested Set is similiar to Tree, but with
# the added feature that you can select the children and all of their descendents with
# a single query. A good use case for this is a threaded post system, where you want
# to display every reply to a comment without multiple selects.
#
# A Google search for "Nested Set" should point you to in the right direction to explain the
# database theory. I figured out a bunch of this from
# http://threebit.net/tutorials/nestedset/tutorial1.html
#
# Instead of picturing a leaf node structure with children pointing back to their parent,
# the best way to imagine how this works is to think of the parent entity surrounding all
# of its children, and its parent surrounding it, etc. Assuming that they are lined up
# horizontally, we store the left and right boundries in the database.
#
# Imagine:
# root
# |_ Child 1
# |_ Child 1.1
# |_ Child 1.2
# |_ Child 2
# |_ Child 2.1
# |_ Child 2.2
#
# If my cirlces in circles description didn't make sense, check out this sweet
# ASCII art:
#
# ___________________________________________________________________
# | Root |
# | ____________________________ ____________________________ |
# | | Child 1 | | Child 2 | |
# | | __________ _________ | | __________ _________ | |
# | | | C 1.1 | | C 1.2 | | | | C 2.1 | | C 2.2 | | |
# 1 2 3_________4 5________6 7 8 9_________10 11_______12 13 14
# | |___________________________| |___________________________| |
# |___________________________________________________________________|
#
# The numbers represent the left and right boundries. The table then might
# look like this:
# ID | PARENT | LEFT | RIGHT | DATA
# 1 | 0 | 1 | 14 | root
# 2 | 1 | 2 | 7 | Child 1
# 3 | 2 | 3 | 4 | Child 1.1
# 4 | 2 | 5 | 6 | Child 1.2
# 5 | 1 | 8 | 13 | Child 2
# 6 | 5 | 9 | 10 | Child 2.1
# 7 | 5 | 11 | 12 | Child 2.2
#
# So, to get all children of an entry, you
# SELECT * WHERE CHILD.LEFT IS BETWEEN PARENT.LEFT AND PARENT.RIGHT
#
# To get the count, it's <tt>(LEFT - RIGHT + 1)/2</tt>, etc.
#
# To get the direct parent, it falls back to using the +PARENT_ID+ field.
#
# There are instance methods for all of these.
#
# The structure is good if you need to group things together; the downside is that
# keeping data integrity is a pain, and both adding and removing an entry
# require a full table write.
#
# This sets up a +before_destroy+ callback to prune the tree correctly if one of its
# elements gets deleted.
#
module ClassMethods
# Configuration options are:
#
# * +parent_column+ - specifies the column name to use for keeping the position integer (default: +parent_id+)
# * +left_column+ - column name for left boundry data, default +lft+
# * +right_column+ - column name for right boundry data, default +rgt+
# * +scope+ - restricts what is to be considered a list. Given a symbol, it'll attach <tt>_id</tt>
# (if it hasn't already been added) and use that as the foreign key restriction. It's also possible
# to give it an entire string that is interpolated if you need a tighter scope than just a foreign key.
# Example: <tt>acts_as_nested_set :scope => 'todo_list_id = #{todo_list_id} AND completed = 0'</tt>
def acts_as_nested_set(options = {})
configuration = { :parent_column => "parent_id", :left_column => "lft", :right_column => "rgt", :scope => "1 = 1" }
configuration.update(options) if options.is_a?(Hash)
configuration[:scope] = "#{configuration[:scope]}_id".intern if configuration[:scope].is_a?(Symbol) && configuration[:scope].to_s !~ /_id$/
if configuration[:scope].is_a?(Symbol)
scope_condition_method = %(
def scope_condition
if #{configuration[:scope].to_s}.nil?
"#{configuration[:scope].to_s} IS NULL"
else
"#{configuration[:scope].to_s} = \#{#{configuration[:scope].to_s}}"
end
end
)
else
scope_condition_method = "def scope_condition() \"#{configuration[:scope]}\" end"
end
class_eval <<-EOV
include ActiveRecord::Acts::NestedSet::InstanceMethods
#{scope_condition_method}
def left_col_name() "#{configuration[:left_column]}" end
def right_col_name() "#{configuration[:right_column]}" end
def parent_column() "#{configuration[:parent_column]}" end
EOV
end
end
module InstanceMethods
# Returns +true+ is this is a root node.
def root?
parent_id = self[parent_column]
(parent_id == 0 || parent_id.nil?) && (self[left_col_name] == 1) && (self[right_col_name] > self[left_col_name])
end
# Returns +true+ is this is a child node
def child?
parent_id = self[parent_column]
!(parent_id == 0 || parent_id.nil?) && (self[left_col_name] > 1) && (self[right_col_name] > self[left_col_name])
end
# Returns +true+ if we have no idea what this is
def unknown?
!root? && !child?
end
# Adds a child to this object in the tree. If this object hasn't been initialized,
# it gets set up as a root node. Otherwise, this method will update all of the
# other elements in the tree and shift them to the right, keeping everything
# balanced.
def add_child( child )
self.reload
child.reload
if child.root?
raise "Adding sub-tree isn\'t currently supported"
else
if ( (self[left_col_name] == nil) || (self[right_col_name] == nil) )
# Looks like we're now the root node! Woo
self[left_col_name] = 1
self[right_col_name] = 4
# What do to do about validation?
return nil unless self.save
child[parent_column] = self.id
child[left_col_name] = 2
child[right_col_name]= 3
return child.save
else
# OK, we need to add and shift everything else to the right
child[parent_column] = self.id
right_bound = self[right_col_name]
child[left_col_name] = right_bound
child[right_col_name] = right_bound + 1
self[right_col_name] += 2
self.class.base_class.transaction {
self.class.base_class.update_all( "#{left_col_name} = (#{left_col_name} + 2)", "#{scope_condition} AND #{left_col_name} >= #{right_bound}" )
self.class.base_class.update_all( "#{right_col_name} = (#{right_col_name} + 2)", "#{scope_condition} AND #{right_col_name} >= #{right_bound}" )
self.save
child.save
}
end
end
end
# Returns the number of nested children of this object.
def children_count
return (self[right_col_name] - self[left_col_name] - 1)/2
end
# Returns a set of itself and all of its nested children
def full_set
self.class.base_class.find(:all, :conditions => "#{scope_condition} AND (#{left_col_name} BETWEEN #{self[left_col_name]} and #{self[right_col_name]})" )
end
# Returns a set of all of its children and nested children
def all_children
self.class.base_class.find(:all, :conditions => "#{scope_condition} AND (#{left_col_name} > #{self[left_col_name]}) and (#{right_col_name} < #{self[right_col_name]})" )
end
# Returns a set of only this entry's immediate children
def direct_children
self.class.base_class.find(:all, :conditions => "#{scope_condition} and #{parent_column} = #{self.id}", :order => left_col_name)
end
# Prunes a branch off of the tree, shifting all of the elements on the right
# back to the left so the counts still work.
def before_destroy
return if self[right_col_name].nil? || self[left_col_name].nil?
dif = self[right_col_name] - self[left_col_name] + 1
self.class.base_class.transaction {
self.class.base_class.delete_all( "#{scope_condition} and #{left_col_name} > #{self[left_col_name]} and #{right_col_name} < #{self[right_col_name]}" )
self.class.base_class.update_all( "#{left_col_name} = (#{left_col_name} - #{dif})", "#{scope_condition} AND #{left_col_name} >= #{self[right_col_name]}" )
self.class.base_class.update_all( "#{right_col_name} = (#{right_col_name} - #{dif} )", "#{scope_condition} AND #{right_col_name} >= #{self[right_col_name]}" )
}
end
end
end
end
end