Enumerable#in_order_of

activerecord/lib/active_record/relation/finder_methods.rb

@@ -520,10 +520,7 @@ def find_some_ordered(ids)
         result = except(:limit, :offset).where(primary_key => ids).records
 
         if result.size == ids.size
-          pk_type = @klass.type_for_attribute(primary_key)
-
-          records_by_id = result.index_by(&:id)
-          ids.map { |id| records_by_id.fetch(pk_type.cast(id)) }
+          result.in_order_of(:id, ids.map { |id| @klass.type_for_attribute(primary_key).cast(id) })
         else
           raise_record_not_found_exception!(ids, result.size, ids.size)
         end

activesupport/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Add `Enumerable#in_order_of` to put an Enumerable in a certain order by a key.
+
+    *DHH*
+
 *   `ActiveSupport::Inflector.camelize` behaves expected when provided a symbol `:upper` or `:lower` argument. Matches
     `String#camelize` behavior.
 

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -191,6 +191,18 @@ def pick(*keys)
   def compact_blank
     reject(&:blank?)
   end
+
+  # Returns a new +Array+ where the order has been set to that provided in the +series+, based on the +key+ of the
+  # objects in the original enumerable.
+  #
+  #   [ Person.find(5), Person.find(3), Person.find(1) ].in_order_of(:id, [ 1, 5, 3 ])
+  #   => [ Person.find(1), Person.find(5), Person.find(3) ]
+  #
+  # If the +series+ include keys that have no corresponding element in the Enumerable, these are ignored.
+  # If the Enumerable has additional elements that aren't named in the +series+, these are not included in the result.
+  def in_order_of(key, series)
+    index_by(&key).values_at(*series).compact
+  end
 end
 
 class Hash

activesupport/test/core_ext/enumerable_test.rb

@@ -284,4 +284,19 @@ def test_hash_compact_blank!
     values.compact_blank!
     assert_equal({ b: 1, f: true }, values)
   end
+
+  def test_in_order_of
+    values = [ Payment.new(5), Payment.new(1), Payment.new(3) ]
+    assert_equal [ Payment.new(1), Payment.new(5), Payment.new(3) ], values.in_order_of(:price, [ 1, 5, 3 ])
+  end
+
+  def test_in_order_of_ignores_missing_series
+    values = [ Payment.new(5), Payment.new(1), Payment.new(3) ]
+    assert_equal [ Payment.new(1), Payment.new(5), Payment.new(3) ], values.in_order_of(:price, [ 1, 2, 4, 5, 3 ])
+  end
+
+  def test_in_order_of_drops_elements_not_named_in_series
+    values = [ Payment.new(5), Payment.new(1), Payment.new(3) ]
+    assert_equal [ Payment.new(1), Payment.new(5) ], values.in_order_of(:price, [ 1, 5 ])
+  end
 end