Use Active Support lazy load hooks

Extend `ActiveRecord::Base` functionality only after `ActiveRecord` has
been fully loaded.

Also:
- Require Railtie as suggested by APIs
- Patch DBConsole only if needed
- Move application configuration check in an after initialize lazy load hook
  to be sure that `Rails.application` is available at the moment of the check

Ref:
- thoughtbot/factory_bot_rails#426
- https://edgeapi.rubyonrails.org/classes/Rails/Railtie.html#class-Rails::Railtie-label-Creating+a+Railtie

Close #231

lib/chrono_model.rb

@@ -2,13 +2,17 @@
 
 require 'active_record'
 
+require 'chrono_model/chrono'
 require 'chrono_model/conversions'
 require 'chrono_model/patches'
 require 'chrono_model/adapter'
 require 'chrono_model/time_machine'
 require 'chrono_model/time_gate'
 require 'chrono_model/version'
 
+require 'chrono_model/railtie' if defined?(Rails::Railtie)
+require 'chrono_model/db_console' if defined?(Rails::DBConsole) && Rails.version < '7.1'
+
 module ChronoModel
   class Error < ActiveRecord::ActiveRecordError # :nodoc:
   end
@@ -33,59 +37,30 @@ def self.history_models
   end
 end
 
-if defined?(Rails::Railtie)
-  require 'chrono_model/railtie'
-end
+ActiveSupport.on_load :active_record do
+  extend ChronoModel::Chrono
 
-ActiveRecord::Base.instance_eval do
-  # Checks whether this Active Recoed model is backed by a temporal table
-  #
-  def chrono?
-    return false unless connection.respond_to? :is_chrono?
+  # Hooks into Association#scope to pass the As-Of time automatically
+  # to methods that load associated ChronoModel records.
+  ActiveRecord::Associations::Association.prepend ChronoModel::Patches::Association
 
-    connection.is_chrono?(table_name)
-  end
-end
+  # Hooks into Relation#build_arel to use `:joins` on your ChronoModels
+  # and join data from associated records As-Of time.
+  ActiveRecord::Relation.prepend ChronoModel::Patches::Relation
 
-# Hooks into Association#scope to pass the As-Of time automatically
-# to methods that load associated ChronoModel records.
-#
-ActiveRecord::Associations::Association.instance_eval do
-  prepend ChronoModel::Patches::Association
-end
+  # Hooks in two points of the AR Preloader to preload As-Of time records of
+  # associated ChronoModels. is used by `.includes`, `.preload`, and `.eager_load`.
+  ActiveRecord::Associations::Preloader.prepend ChronoModel::Patches::Preloader
 
-# Hooks into Relation#build_arel to use :joins on your ChronoModels
-# and join data from associated records As-Of time.
-#
-ActiveRecord::Relation.instance_eval do
-  prepend ChronoModel::Patches::Relation
-end
+  ActiveRecord::Associations::Preloader::Association.prepend ChronoModel::Patches::Preloader::Association
 
-# Hooks in two points of the AR Preloader to preload As-Of time records of
-# associated ChronoModels. is used by .includes, .preload and .eager_load.
-#
-ActiveRecord::Associations::Preloader.instance_eval do
-  prepend ChronoModel::Patches::Preloader
-end
-
-ActiveRecord::Associations::Preloader::Association.instance_eval do
-  prepend ChronoModel::Patches::Preloader::Association
-end
+  ActiveRecord::Associations::Preloader::ThroughAssociation.prepend ChronoModel::Patches::Preloader::ThroughAssociation
 
-ActiveRecord::Associations::Preloader::ThroughAssociation.instance_eval do
-  prepend ChronoModel::Patches::Preloader::ThroughAssociation
+  ActiveRecord::Batches::BatchEnumerator.prepend ChronoModel::Patches::Batches::BatchEnumerator
 end
 
-ActiveRecord::Batches::BatchEnumerator.instance_eval do
-  prepend ChronoModel::Patches::Batches::BatchEnumerator
-end
+ActiveSupport.on_load :after_initialize do
+  next if Rails.application.config.active_record.schema_format == :sql
 
-if defined?(Rails::DBConsole) && Rails.version < '7.1'
-  Rails::DBConsole.instance_eval do
-    if Rails.version < '6.1'
-      prepend ChronoModel::Patches::DBConsole::Config
-    else
-      prepend ChronoModel::Patches::DBConsole::DbConfig
-    end
-  end
+  raise 'In order to use ChronoModel, set `config.active_record.schema_format` to `:sql`'
 end

lib/chrono_model/chrono.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module ChronoModel
+  # A module to add to ActiveRecord::Base to check if they are backed by
+  # temporal tables.
+  module Chrono
+    # Checks whether this Active Record model is backed by a temporal table
+    #
+    # @return [Boolean] false if the connection does not respond to is_chrono?
+    #   the result of connection.is_chrono?(table_name) otherwise
+    def chrono?
+      return false unless connection.respond_to? :is_chrono?
+
+      connection.is_chrono?(table_name)
+    end
+  end
+end

lib/chrono_model/db_console.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require 'chrono_model/patches/db_console'
+
+if Rails.version < '6.1'
+  Rails::DBConsole.prepend ChronoModel::Patches::DBConsole::Config
+else
+  Rails::DBConsole.prepend ChronoModel::Patches::DBConsole::DbConfig
+end

lib/chrono_model/patches.rb

@@ -7,5 +7,4 @@
 require 'chrono_model/patches/relation'
 require 'chrono_model/patches/preloader'
 require 'chrono_model/patches/association'
-require 'chrono_model/patches/db_console'
 require 'chrono_model/patches/batches'

lib/chrono_model/railtie.rb

@@ -6,14 +6,6 @@ module ChronoModel
   class Railtie < ::Rails::Railtie
     TASKS_CLASS = ActiveRecord::Tasks::ChronomodelDatabaseTasks
 
-    def task_config
-      if Rails.version < '6.1'
-        ActiveRecord::Tasks::DatabaseTasks.current_config.with_indifferent_access
-      else
-        ActiveRecord::Base.connection_db_config
-      end
-    end
-
     # Register our database tasks under our adapter name
     if Rails.version < '5.2'
       ActiveRecord::Tasks::DatabaseTasks.register_task(/chronomodel/, TASKS_CLASS)
@@ -22,8 +14,12 @@ def task_config
     end
 
     rake_tasks do
-      if Rails.application.config.active_record.schema_format != :sql
-        raise 'In order to use ChronoModel, config.active_record.schema_format must be :sql!'
+      def task_config
+        if Rails.version < '6.1'
+          ActiveRecord::Tasks::DatabaseTasks.current_config.with_indifferent_access
+        else
+          ActiveRecord::Base.connection_db_config
+        end
       end
 
       if Rails.version < '6.1'