IndexTree

This Gem eagerly loads trees by indexing the nodes of the tree. The number of queries needed for loading a tree is N, Where 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:

Models definitions:

class Equation < ActiveRecord::Base
    acts_as_indexed_node :root => true do
        has_many :expressions
    end
  
    has_one :not_tree_association_a
    
    def traverse
       expression.traverse
    end        
end


class Expression < ActiveRecord::Base
    belongs_to :equation, inverse_of: :expressions
    
    acts_as_indexed_node do
        has_many :expressions
    end
    
    has_one :not_tree_association_b
    
    def traverse
        expressions.map(&:traverse)
    end
end

Database initialization:

                 +-----------+                               +-----------+
                 |Equation  1|                               |Equation  2|
                 +-----+-----+                               +-----+-----+
                       |                                           |
                       v                                           v
                 +-----------+                               +-----------+
                 |Expression1|                               |Expression6|
                 +-+-------+-+                               +-+-------+-+
                   ^       ^                                   ^       ^
                   |       |                                   |       |
           +-------+       +-------+                   +-------+       +-------+
           |                       |                   |                       |
           |                       |                   |                       |
     +-----+-----+           +-----+-----+       +-----+-----+           +-----+-----+
     |Expression3|           |Expression2|       |Expression8|           |Expression7|
     +-----------+           +-----------+       +-----------+           +-----------+
                               ^       ^                                   ^       ^
                               |       |                                   |       |
                       +-------+       +-------+                   +-------+       +-------+
                       |                       |                   |                       |
                       |                       |                   |                       |
                 +-----+-----+           +-----+-----+       +-----+-----+          +------+-----+
                 |Expression4|           |Expression5|       |Expression9|          |Expression10|
                 +-----------+           +-----------+       +-----------+          +------------+                       

Traversal example without tree pre-loading:

Equation.find(1).traverse

Those are the queries that is executed:

Equation Load (0.2ms)  SELECT  "equations".* FROM "equations"   ORDER BY "equations"."id" ASC LIMIT 1
Expression Load (0.2ms)  SELECT  "expressions".* FROM "expressions"  WHERE "expressions"."id" = ? LIMIT 1  [["id", 1]]
Expression Load (0.1ms)  SELECT "expressions".* FROM "expressions"  WHERE "expressions"."expression_id" = ?  [["expression_id", 1]]
Expression Load (0.1ms)  SELECT "expressions".* FROM "expressions"  WHERE "expressions"."expression_id" = ?  [["expression_id", 2]]
Expression Load (0.1ms)  SELECT "expressions".* FROM "expressions"  WHERE "expressions"."expression_id" = ?  [["expression_id", 4]]
Expression Load (0.1ms)  SELECT "expressions".* FROM "expressions"  WHERE "expressions"."expression_id" = ?  [["expression_id", 5]]
Expression Load (0.1ms)  SELECT "expressions".* FROM "expressions"  WHERE "expressions"."expression_id" = ?  [["expression_id", 3]]

It can be improved with eager loading such as 'includes', but eager loading will be fixed to the tree height.

Traversal example with tree pre-loading:

Equation.find(1).preload_tree.traverse

The statement fetches only the objects in the Equation1 tree in two queries:

Equation Load (0.1ms)  SELECT  "equations".* FROM "equations"   ORDER BY "equations"."id" ASC LIMIT 1
Expression Load (0.2ms)  SELECT "expressions".* FROM "expressions" 
INNER JOIN "index_tree_index_nodes" ON "index_tree_index_nodes"."node_element_id" = "expressions"."id" 
AND "index_tree_index_nodes"."node_element_type" = 'Expression' 
WHERE "index_tree_index_nodes"."root_element_type" = 'Equation' AND "index_tree_index_nodes"."root_element_id" IN (1)

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)

Installation

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)

Declaration

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

The following associations are supported:

 belongs_to
 belongs_to :class, polymorphic: true
 has_one
 has_many

The following types of inheritance are supported:

STI 
Polymorphic associations

Options:

:root   Used to declare a root model(default is false)

Usage

RootModel.find(1).preload_tree
RootModel.all.preload_tree
RootModel.where(color: 'red').all.preload_tree