Fixing concurrent execution of fields resolution (#3119)

Fixes #3029

src/OrchardCore.Modules/OrchardCore.Apis.GraphQL/Services/SerialDocumentExecuter.cs

@@ -0,0 +1,36 @@
+using GraphQL;
+using GraphQL.Execution;
+using GraphQL.Language.AST;
+using System;
+
+namespace OrchardCore.Apis.GraphQL.Services
+{
+    /// <summary>
+    /// Defines a custom execution strategy for queries such that async lambdas are not executed in parallel.
+    /// c.f. https://github.com/OrchardCMS/OrchardCore/issues/3029
+    /// </summary>
+    public class SerialDocumentExecuter : DocumentExecuter
+    {
+        private static IExecutionStrategy ParallelExecutionStrategy = new ParallelExecutionStrategy();
+        private static IExecutionStrategy SerialExecutionStrategy = new SerialExecutionStrategy();
+        private static IExecutionStrategy SubscriptionExecutionStrategy = new SubscriptionExecutionStrategy();
+
+        protected override IExecutionStrategy SelectExecutionStrategy(ExecutionContext context)
+        {
+            switch (context.Operation.OperationType)
+            {
+                case OperationType.Query:
+                    return SerialExecutionStrategy;
+
+                case OperationType.Mutation:
+                    return SerialExecutionStrategy;
+
+                case OperationType.Subscription:
+                    return SubscriptionExecutionStrategy;
+
+                default:
+                    throw new InvalidOperationException($"Unexpected OperationType {context.Operation.OperationType}");
+            }
+        }
+    }
+}

src/OrchardCore.Modules/OrchardCore.Apis.GraphQL/Startup.cs

@@ -29,7 +29,7 @@ public Startup(IShellConfiguration configuration,
         public override void ConfigureServices(IServiceCollection services)
         {
             services.AddSingleton<IDependencyResolver, RequestServicesDependencyResolver>();
-            services.AddSingleton<IDocumentExecuter, DocumentExecuter>();
+            services.AddSingleton<IDocumentExecuter, SerialDocumentExecuter>();
             services.AddSingleton<IDocumentWriter, DocumentWriter>();
 
             services.AddScoped<ISchemaFactory, SchemaService>();