passing an instance of an AR object to `find` is deprecated

please pass the id of the AR object by calling `.id` on the model first.

5 files changed, 13 insertions, 6 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 68c348e8d5..d52c2f711e 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,6 @@
+* Passing an Active Record object to `find` is now deprecated.  Call `.id`
+  on the object first.
+
 * Passing an Active Record object to `exists?` is now deprecated.  Call `.id`
   on the object first.
 
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 180bc64e3a..c2b9dc08fe 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -421,7 +421,11 @@ module ActiveRecord
     end
 
     def find_one(id)
-      id = id.id if ActiveRecord::Base === id
+      if ActiveRecord::Base === id
+        id = id.id
+        ActiveSupport::Deprecation.warn "You are passing an instance of ActiveRecord::Base to `find`." \
+          "Please pass the id of the object by calling `.id`"
+      end
 
       column = columns_hash[primary_key]
       substitute = connection.substitute_at(column, bind_values.length)
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 5522a33b79..416a39ea4c 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -407,19 +407,19 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_load_has_one_quotes_table_and_column_names
-    michael = Person.all.merge!(:includes => :favourite_reference).find(people(:michael))
+    michael = Person.all.merge!(:includes => :favourite_reference).find(people(:michael).id)
     references(:michael_unicyclist)
     assert_no_queries{ assert_equal references(:michael_unicyclist), michael.favourite_reference}
   end
 
   def test_eager_load_has_many_quotes_table_and_column_names
-    michael = Person.all.merge!(:includes => :references).find(people(:michael))
+    michael = Person.all.merge!(:includes => :references).find(people(:michael).id)
     references(:michael_magician,:michael_unicyclist)
     assert_no_queries{ assert_equal references(:michael_magician,:michael_unicyclist), michael.references.sort_by(&:id) }
   end
 
   def test_eager_load_has_many_through_quotes_table_and_column_names
-    michael = Person.all.merge!(:includes => :jobs).find(people(:michael))
+    michael = Person.all.merge!(:includes => :jobs).find(people(:michael).id)
     jobs(:magician, :unicyclist)
     assert_no_queries{ assert_equal jobs(:unicyclist, :magician), michael.jobs.sort_by(&:id) }
   end
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index ab71b2af9d..3b4b4c92f0 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -637,7 +637,7 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_find_with_list_of_ar
     author = Author.first
-    authors = Author.find([author])
+    authors = Author.find([author.id])
     assert_equal author, authors.first
   end
 
diff --git a/activerecord/test/cases/validations/uniqueness_validation_test.rb b/activerecord/test/cases/validations/uniqueness_validation_test.rb
index 74c696c858..18221cc73d 100644
--- a/activerecord/test/cases/validations/uniqueness_validation_test.rb
+++ b/activerecord/test/cases/validations/uniqueness_validation_test.rb
@@ -223,7 +223,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert t_utf8.save, "Should save t_utf8 as unique"
 
     # If database hasn't UTF-8 character set, this test fails
-    if Topic.all.merge!(:select => 'LOWER(title) AS title').find(t_utf8).title == "я тоже уникальный!"
+    if Topic.all.merge!(:select => 'LOWER(title) AS title').find(t_utf8.id).title == "я тоже уникальный!"
       t2_utf8 = Topic.new("title" => "я тоже УНИКАЛЬНЫЙ!")
       assert !t2_utf8.valid?, "Shouldn't be valid"
       assert !t2_utf8.save, "Shouldn't save t2_utf8 as unique"