Added preload_tree method

Author: wollistik

CHANGELOG.md

@@ -1,3 +1,6 @@
+### Version 3.2.0
+- Added #preload_tree method to preload the parent/child relations of a single node
+
 ### Version 3.1.0
 - Rails 7 support
 

README.md

@@ -134,7 +134,7 @@ __Additional methods:__
 __Utility methods:__
   * `root?` - returns true if this node is a root node
   * `leaf?` - returns true if this node is a leave node
-
+  * `preload_tree` - fetches all descendants of this node and assignes the proper parent/children associations. You are then able to traverse the tree through the children/parent association without querying the database again.
 
 ## Customizing the recursion
 

lib/acts_as_recursive_tree/acts_macro.rb

@@ -8,7 +8,8 @@ module ActsMacro
     # * <tt>foreign_key</tt> - specifies the column name to use for tracking
     # of the tree (default: +parent_id+)
     def recursive_tree(parent_key: :parent_id, parent_type_column: nil)
-      class_attribute :_recursive_tree_config
+      class_attribute(:_recursive_tree_config, instance_writer: false)
+
       self._recursive_tree_config = Config.new(
         model_class: self,
         parent_key: parent_key.to_sym,

lib/acts_as_recursive_tree/model.rb

@@ -91,6 +91,14 @@ def leaf?
       children.none?
     end
 
+    #
+    # Fetches all descendants of this node and assigns the parent/children associations
+    #
+    def preload_tree
+      ActsAsRecursiveTree::Preloaders::Descendants.new(self).preload!
+      true
+    end
+
     def base_class
       self.class.base_class
     end

lib/acts_as_recursive_tree/preloaders/descendants.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module ActsAsRecursiveTree
+  module Preloaders
+    #
+    # Preloads all descendants records for a given node and sets the parent and child associations on each record
+    # based on the preloaded data. After this, calling #parent or #children will not trigger a database query.
+    #
+    class Descendants
+      def initialize(node)
+        @node = node
+        @parent_key = node._recursive_tree_config.parent_key
+      end
+
+      def preload!
+        apply_records(@node)
+      end
+
+      private
+
+      def records
+        @records ||= @node.descendants.to_a
+      end
+
+      def apply_records(parent_node)
+        children = records.select { |child| child.send(@parent_key) == parent_node.id }
+
+        parent_node.association(:children).target = children
+
+        children.each do |child|
+          child.association(:parent).target = parent_node
+          apply_records(child)
+        end
+      end
+    end
+  end
+end

lib/acts_as_recursive_tree/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module ActsAsRecursiveTree
-  VERSION = '3.1.0'
+  VERSION = '3.2.0'
 end

spec/acts_as_recursive_tree/preloaders/descendants_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ActsAsRecursiveTree::Preloaders::Descendants do
+  include TreeMethods
+
+  let(:preloader) { described_class.new(root.reload) }
+  let(:root) { create_tree(2) }
+  let(:children) { root.children }
+
+  describe '#preload! will set the associations target attribute' do
+    before do
+      preloader.preload!
+    end
+
+    it 'sets the children assoction' do
+      children.each do |child|
+        expect(child.association(:children).target).not_to be_nil
+      end
+    end
+
+    it 'sets the parent assoction' do
+      children.each do |child|
+        expect(child.association(:parent).target).not_to be_nil
+      end
+    end
+  end
+end

spec/model/node_spec.rb

@@ -3,16 +3,7 @@
 require 'spec_helper'
 
 describe Node do
-  def create_tree(max_level, current_level = 0, node = nil)
-    node = Node.create!(name: 'root') if node.nil?
-
-    1.upto(max_level - current_level) do |index|
-      child = node.children.create!(name: "child #{index} - level #{current_level}")
-      create_tree(max_level, current_level + 1, child)
-    end
-
-    node
-  end
+  include TreeMethods
 
   before do
     @root  = create_tree(3)

spec/spec_helper.rb

@@ -11,6 +11,10 @@
 
 require 'database_cleaner'
 
+# Requires supporting ruby files with custom matchers and macros, etc,
+# in spec/support/ and its subdirectories.
+Dir[File.join(__dir__, 'support/**/*.rb')].sort.each { |f| require f }
+
 # This file was generated by the `rspec --init` command. Conventionally, all
 # specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
 # The generated `.rspec` file contains `--require spec_helper` which will cause

spec/support/tree_methods.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+# Helper methods for simple tree creation
+module TreeMethods
+  def create_tree(max_level, current_level = 0, node = nil)
+    node = Node.create!(name: 'root') if node.nil?
+
+    1.upto(max_level - current_level) do |index|
+      child = node.children.create!(name: "child #{index} - level #{current_level}")
+      create_tree(max_level, current_level + 1, child)
+    end
+
+    node
+  end
+end