This Gem eager loads trees by indexing the nodes of the tree. The number of queries needed to load a tree is N, when N is the number of different models(ActiveRecords) in the tree.
Each inner object in the tree have an index node instance that is connecting it to the root. When the root of the tree is loaded, only the objects that are in the tree are fetched(Pruning). The index nodes are created when the root element is saved and stored in the IndexNode model.
Example:
class Equation < ActiveRecord::Base
acts_as_indexed_node :root => true do
has_many :expressions
end
has_one :not_tree_association_a
end
class Expression < ActiveRecord::Base
acts_as_indexed_node do
has_many :expressions
end
has_one :not_tree_association_b
end
+----------+ +----------+
|Equation 1| |Equation 2|
+-+------+-+ +-+------+-+
| | | |
+-------+ +-------+ +-------+ +-------+
| | | |
v v v v
+-----------+ +-----------+ +-----------+ +-----------+
|Expression1| |Expression2| |Expression5| |Expression6|
+-----------+ +-+-------+-+ +-----------+ +-+-------+-+
| | | |
+-------+ +-------+ +-------+ +-------+
| | | |
v v v v
+-----------+ +-----------+ +-----------+ +-----------+
|Expression3| |Expression4| |Expression7| |Expression8|
+-----------+ +-----------+ +-----------+ +-----------+
The following statement fetches only the objects in the Equation1 tree in two queries:
Equation.find(1).preload_tree
One query to fetch Equations, and the second query is to fetch Expressions(Doesn't matter how deep is the tree it is still one query)
Add this line to your application's Gemfile:
gem 'index_tree'And then execute:
$ bundle
$ rake db:migrate
There is a migration which creates index_tree_index_node table(IndexNode model)
All the models should be loaded in the Rails application, before using the preload_tree.
class RootNode < ActiveRecord::Base
acts_as_indexed_node :root => true do
has_many :child_nodes, dependent: :destroy
end
end
belongs_to
belongs_to :class, polymorphic: true
has_one
has_many
STI
Polymorphic associations
:root Used to declare a root model(default is false)
RootModel.find(1).preload_tree
RootModel.all.preload_tree
RootModel.where(color: 'red').all.preload_tree