Fix belongs_to reify for associations that use a different foreign_key

CHANGELOG.md

@@ -24,6 +24,8 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
   matchers to work with custom version association names
 - [#929](https://github.com/airblade/paper_trail/pull/929) -
   Fix error calling private method in rails 4.0
+- [#938](https://github.com/airblade/paper_trail/pull/938) - Fix bug where
+  non-standard foreign key names broke belongs_to associations
 
 ## 6.0.2 (2016-12-13)
 

lib/paper_trail/reifiers/belongs_to.rb

@@ -6,7 +6,7 @@ module BelongsTo
       class << self
         # @api private
         def reify(assoc, model, options, transaction_id)
-          id = model.send(assoc.association_foreign_key)
+          id = model.send(assoc.foreign_key)
           version = load_version(assoc, id, transaction_id, options[:version_at])
           record = load_record(assoc, id, options, version)
           model.send("#{assoc.name}=".to_sym, record)

test/dummy/app/models/person.rb

@@ -1,6 +1,7 @@
 class Person < ActiveRecord::Base
   has_many :authorships, foreign_key: :author_id, dependent: :destroy
   has_many :books, through: :authorships
+  belongs_to :mentor, class_name: "Person", foreign_key: :mentor_id
   has_paper_trail
 
   # Convert strings to TimeZone objects when assigned

test/dummy/db/migrate/20110208155312_set_up_test_tables.rb

@@ -166,6 +166,7 @@ def up
     create_table :people, force: true do |t|
       t.string :name
       t.string :time_zone
+      t.integer :mentor_id
     end
 
     create_table :editorships, force: true do |t|

test/dummy/db/schema.rb

@@ -174,8 +174,9 @@
   end
 
   create_table "people", force: :cascade do |t|
-    t.string "name"
-    t.string "time_zone"
+    t.string  "name"
+    t.string  "time_zone"
+    t.integer "mentor_id"
   end
 
   create_table "post_versions", force: :cascade do |t|