Return Not found Ids in ActiveRecord::NotFound

activerecord/lib/active_record/associations/collection_association.rb

@@ -59,7 +59,9 @@ def ids_writer(ids)
           r.send(reflection.association_primary_key)
         end.values_at(*ids).compact
         if records.size != ids.size
-          klass.all.raise_record_not_found_exception!(ids, records.size, ids.size, reflection.association_primary_key)
+          found_ids = records.map { |record| record.send(reflection.association_primary_key) }
+          not_found_ids = ids - found_ids
+          klass.all.raise_record_not_found_exception!(ids, records.size, ids.size, reflection.association_primary_key, not_found_ids)
         else
           replace(records)
         end

activerecord/lib/active_record/relation/finder_methods.rb

@@ -330,7 +330,7 @@ def exists?(conditions = :none)
     # of results obtained should be provided in the +result_size+ argument and
     # the expected number of results should be provided in the +expected_size+
     # argument.
-    def raise_record_not_found_exception!(ids = nil, result_size = nil, expected_size = nil, key = primary_key) # :nodoc:
+    def raise_record_not_found_exception!(ids = nil, result_size = nil, expected_size = nil, key = primary_key, not_found_ids = nil) # :nodoc:
       conditions = arel.where_sql(@klass)
       conditions = " [#{conditions}]" if conditions
       name = @klass.name
@@ -344,8 +344,8 @@ def raise_record_not_found_exception!(ids = nil, result_size = nil, expected_siz
         raise RecordNotFound.new(error, name, key, ids)
       else
         error = "Couldn't find all #{name.pluralize} with '#{key}': ".dup
-        error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})"
-
+        error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})."
+        error << " Couldn't find #{name.pluralize(not_found_ids.size)} with #{key.to_s.pluralize(not_found_ids.size)} #{not_found_ids.join(', ')}." if not_found_ids
         raise RecordNotFound.new(error, name, primary_key, ids)
       end
     end

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -891,7 +891,8 @@ def test_collection_singular_ids_setter_raises_exception_when_invalid_ids_set
     company = companies(:rails_core)
     ids = [Developer.first.id, -9999]
     e = assert_raises(ActiveRecord::RecordNotFound) { company.developer_ids = ids }
-    assert_match(/Couldn't find all Developers with 'id'/, e.message)
+    msg = "Couldn't find all Developers with 'id': (1, -9999) (found 1 results, but was looking for 2). Couldn't find Developer with id -9999."
+    assert_equal(msg, e.message)
   end
 
   def test_collection_singular_ids_setter_raises_exception_when_invalid_ids_set_with_changed_primary_key
@@ -905,7 +906,8 @@ def test_collection_singular_ids_through_setter_raises_exception_when_invalid_id
     author = authors(:david)
     ids = [categories(:general).name, "Unknown"]
     e = assert_raises(ActiveRecord::RecordNotFound) { author.essay_category_ids = ids }
-    assert_equal "Couldn't find all Categories with 'name': (General, Unknown) (found 1 results, but was looking for 2)", e.message
+    msg = "Couldn't find all Categories with 'name': (General, Unknown) (found 1 results, but was looking for 2). Couldn't find Category with name Unknown."
+    assert_equal msg, e.message
   end
 
   def test_build_a_model_from_hm_through_association_with_where_clause

activerecord/test/cases/finder_test.rb

@@ -1153,7 +1153,7 @@ def test_find_some_message_with_custom_primary_key
       e = assert_raises(ActiveRecord::RecordNotFound) do
         model.find "Hello", "World!"
       end
-      assert_equal "Couldn't find all MercedesCars with 'name': (Hello, World!) (found 0 results, but was looking for 2)", e.message
+      assert_equal "Couldn't find all MercedesCars with 'name': (Hello, World!) (found 0 results, but was looking for 2).", e.message
     end
   end