Fix sequential mutations with Dataloader

Author: rmosolgo

lib/graphql/execution/interpreter/runtime.rb

@@ -393,6 +393,12 @@ def evaluate_selections(owner_object, owner_type, is_eager_selection, gathered_s
                 selections_result.merge_into(target_result)
               end
             }
+            # Field resolution may pause the fiber,
+            # so it wouldn't get to the `Resolve` call that happens below.
+            # So instead trigger a run from this outer context.
+            if is_eager_selection
+              @dataloader.run
+            end
           end
 
           selections_result

spec/graphql/dataloader_spec.rb

@@ -319,9 +319,23 @@ def resolve(argument_2:)
       end
     end
 
+    class Mutation3 < GraphQL::Schema::Mutation
+      argument :label, String
+      type String
+
+      def resolve(label:)
+        log = context[:mutation_log] ||= []
+        log << "begin #{label}"
+        dataloader.with(DataObject).load(1)
+        log << "end #{label}"
+        label
+      end
+    end
+
     class Mutation < GraphQL::Schema::Object
       field :mutation_1, mutation: Mutation1
       field :mutation_2, mutation: Mutation2
+      field :mutation_3, mutation: Mutation3
     end
 
     mutation(Mutation)
@@ -403,6 +417,18 @@ def self.included(child_class)
           assert_equal [[:mget, ["5", "6"]], [:mget, ["2", "3"]]], database_log
         end
 
+        it "runs mutations sequentially" do
+          res = schema.execute <<-GRAPHQL
+            mutation {
+              first: mutation3(label: "first")
+              second: mutation3(label: "second")
+            }
+          GRAPHQL
+
+          assert_equal({ "first" => "first", "second" => "second" }, res["data"])
+          assert_equal ["begin first", "end first", "begin second", "end second"], res.context[:mutation_log]
+        end
+
         it "batch-loads" do
           res = schema.execute <<-GRAPHQL
           {