Fix uniqueness validation, #id_in_database can be composite

Until now, specifying uniqueness validations for records that have a composite key fail. This is because uniqueness validation relies on #id_in_database, which didn't yet consider the case when primary key is an array.

Author: paarthmadan

activerecord/lib/active_record/attribute_methods/primary_key.rb

@@ -53,7 +53,11 @@ def id_was
 
       # Returns the primary key column's value from the database.
       def id_in_database
-        attribute_in_database(@primary_key)
+        if self.class.composite_primary_key?
+          @primary_key.map { |col| attribute_in_database(col) }
+        else
+          attribute_in_database(@primary_key)
+        end
       end
 
       def id_for_database # :nodoc:

activerecord/lib/active_record/validations/uniqueness.rb

@@ -25,7 +25,7 @@ def validate_each(record, attribute, value)
         relation = build_relation(finder_class, attribute, value)
         if record.persisted?
           if finder_class.primary_key
-            relation = relation.where.not(finder_class.primary_key => record.id_in_database)
+            relation = relation.where.not(finder_class.primary_key => [record.id_in_database])
           else
             raise UnknownPrimaryKey.new(finder_class, "Cannot validate uniqueness for persisted record without primary key.")
           end

activerecord/test/cases/validations/uniqueness_validation_test.rb

@@ -12,6 +12,7 @@
 require "models/person"
 require "models/essay"
 require "models/keyboard"
+require "models/cpk"
 
 class Wizard < ActiveRecord::Base
   self.abstract_class = true
@@ -811,3 +812,22 @@ def test_index_of_columns_list_and_extra_columns
     end
   end
 end
+
+class UniquenessWithCompositeKey < ActiveRecord::TestCase
+  class BookWithUniqueRevision < Cpk::Book
+    validates :revision, uniqueness: true
+  end
+
+  def test_uniqueness_validation_for_model_with_composite_key
+    book_one = BookWithUniqueRevision.create!(author_id: 1, number: 42, title: "Author 1's book", revision: 36)
+    book_two = BookWithUniqueRevision.create!(author_id: 2, number: 42, title: "Author 2's book", revision: 37)
+
+    assert_not_equal book_one.revision, book_two.revision
+
+    assert_changes("book_two.valid?", from: true, to: false) do
+      book_two.revision = book_one.revision
+    end
+  ensure
+    BookWithUniqueRevision.delete_all
+  end
+end