Generate Entity Relationship Model for ActiveRecord with GraphViz

activerecord_graphviz.rb

namespace :graph do

  desc 'build graph of AR models'
  task models: :environment do
    require 'graphviz'
    Rails.application.eager_load!

    g = GraphViz.new('Models', path: Rails.root.join('tmp').to_s)

    nodes = ObjectSpace.each_object(Class)
      .select { |c| c < ActiveRecord::Base }
      .map { |c| GraphNode.new(g, c) }

    nodes
      .each { |m| m.nodes = nodes }
      .each(&:call)

    g.output(png: "models.png")
  end
end

class GraphNode < Struct.new(:g, :model)
  attr_accessor :nodes
  attr_reader :node
  def initialize(*args)
    super
    @node = g.add_nodes(model.name)
  end

  def call
    add_parents
    add_children
  end

  def add_parents
    reflections(kind: :belongs_to).each do |parent|
      g.add_edges(@node, parent.node, style: "solid" )
    end
  end

  def add_children
    reflections(kind: :has_many).each do |child|
      g.add_edges(@node, child.node, style: "dotted" )
    end

    reflections(kind: :has_one).each do |child|
      g.add_edges(@node, child.node, style: "dotted" )
    end
  end

  def reflections(kind:)
    model.reflections
      .select { |_, assoc| assoc.macro == kind }
      .map { |label, assoc|
        begin
          nodes.find{|n| n.model == assoc.klass}
        rescue NameError => e
          puts '-'*80
          puts "for #{model.name}"
          puts e
          puts '-'*80
          nil
        end
      }.compact
  end
end