Snapshot Tree

Yet another tree implementation of adjacency list structure using recursive query of Postgresql >= 8.4.

The main implementation different among others similar gems is the support of handling multiple effective tree snapshot, for which the parent/child relationship history can all be kept in a single relationship table with different effective date.

Since ActiveRecord doesn't support update of relation table through has_many :through association, the creation of child and parent directly through association are not suported by this gem. Please reference other gems in case if multiple snapshot with effective date handling is not necessary.

Requirements

• PostgreSQL version >= 8.4
• ActiveRecord

Setup

1. Add this line to your application's Gemfile: gem 'snapshot_tree'

2. Run bundle install

3. Add acts_as_tree to your hierarchical model(s), see configuration section below.

   The ActiveRecord associations parent_tree_nodes and child_tree_nodes will be added automatically to ease the creation of tree association records

   class Node < ActiveRecord::Base
     include SnapshotTree::ActsAsTree
     acts_as_tree
   end

4. Add a database migration to store the hierarchy relation for your model. Relation table's name must be the model's table name, followed by "_tree".

   class CreateModelTrees < ActiveRecord::Migration
     def change
       create_table :model_trees do |t|
         t.integer  :child_id
         t.integer  :parent_id
         t.boolean  :is_active       # default field name for :is_active_field option
         t.date     :effective_on    # default field name for :snapshot_field option
   
         t.timestamps
       end
     end
   end

5. Run rake db:migrate

Configuration

When you include acts_as_tree in your model, you can provide a hash to override the following defaults:

• :child_key to override the column name of the child foreign key in relation table. (default: child_id)
• :parent_key to override the column name of the parent foreign key in relation table. (default: parent_id)
• :node_prefix to override the field name prefix of generated field after getting descendent_nodes or ancestor_nodes. (default: node)
• :snapshot_field to override the column name of snapshot effective date in relations table. (default: effective_on)
  • set it to nil will disable effective date filtering when getting tree snapshot.
• :is_active_field to override the column name of snapshot record active status in relation table. (default: is_active)
  • set it to nil will disable active status checking.
• :dependent determines what happens when a node is destroyed. Defaults to nullify.
  • :nullify will simply set the parent column to null. Each child node will be considered a "root" node. This is the default.
  • :delete_all will delete all descendant nodes (which circumvents the destroy hooks)
  • :destroy will destroy all descendant nodes (which runs the destroy hooks on each child node)

Usage

Creation tree association:

grandpa = Node.create(:name => 'grandpa')
parent  = Node.create(:name => 'parent')
child   = Node.create(:name => 'child')

grandpa.child_tree_nodes.create(:child_id => parent.id, :effective_on => '2012-01-01')
child.parent_tree_nodes.create(:parent_id => parent.id, :effective_on => Date.today)

Accessing the tree:

Class methods

• Node.root_nodes returns all root nodes
• Node.leaf_nodes returns all leaf nodes
• Node.descendent_nodes returns all descendent nodes, including children, children's children, ... etc.
• Node.ancestor_nodes returns all ancestor nodes, including parent, grandparent, great grandparent, ... etc.

Instance methods

• Node.root_node returns the root node for this node
• Node.root_node? returns true if this is a root node
• Node.leaf_node? returns true if this is a leaf node
• Node.parent_node returns the parent node for this node
• Node.child_nodes returns an array of direct children node for this node
• Node.descendent_nodes returns all descendent nodes for this node, including children, children's children, ... etc.
• Node.ancestor_nodes returns all ancestor nodes for this node, including parent, grandparent, great grandparent, ... etc.

Extra options

When calling the instance/class methods, you can pass a hash of options to override the default behavour:

• :as_of to query the snapsot tree as of specify effective date, the latest effective date <= this parameter will be used to filter records. This defaults to today.
• :depth to limit to number of level to query, 0 for all levels, 1 for direct children only, 2 for direct children and grand children, ... etc. This defaults to 0.

When calling the class methods, you must pass an model or model id in order to query tree nodes:

Node.descendent_nodes(grandpa, :depth => 1, :as_of => '2010-01-01')

Gem testing

1. Copy spec/database.yml.sample to spec/database.yml and edit to appropriate values
2. Create table 'tree_testing'
3. Run load 'spec/db/schema.rb' in console
4. bundle exec rspec spec/acts_as_tree_spec.rb

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Thanks to

• https://github.com/chrisroberts/acts_as_sane_tree

• https://github.com/mceachen/closure_tree

• Bill Karwin's excellent Models for hierarchical data presentation for a description of different tree storage algorithms.