Added better error when root value cannot be created. (#2598)

ErrorCodes.md

@@ -1,5 +1,5 @@
 | Code   | Category          | Description                                                                                                |
-|--------|-------------------|------------------------------------------------------------------------------------------------------------|
+| ------ | ----------------- | ---------------------------------------------------------------------------------------------------------- |
 | HC0001 | Scalars           | The runtime type is not supported by the scalars ParseValue method.                                        |
 | HC0002 | Scalars           | Either the syntax node is invalid when parsing the literal or the syntax node value has an invalid format. |
 | HC0003 | Apollo Federation | The key attribute is used on the type level without specifying the fieldset.                               |
@@ -18,6 +18,4 @@
 | HC0016 | Execution         | Variable `xyz` got an invalid value.                                                                       |
 | HC0017 | Execution         | Variable `xyz` is not an input type.                                                                       |
 | HC0018 | Execution         | Variable `xyz` is required.                                                                                |
-
-
-
+| HC0019 | Execution         | Unable to create an instance for the operation type (initial value).                                       |

src/HotChocolate/Core/src/Abstractions/ErrorCodes.cs

@@ -25,6 +25,7 @@ public static class Execution
             public const string QueryNotFound = "HC0015";
             public const string TaskProcessingError = "HC0008";
             public const string SyntaxError = "HC0014";
+            public const string CannotCreateRootValue = "HC0019";
         }
 
         public static class Server

src/HotChocolate/Core/src/Execution/Pipeline/OperationExecutionMiddleware.cs

@@ -72,7 +72,7 @@ internal sealed class OperationExecutionMiddleware
 
         private async Task ExecuteOperationAsync(
             IRequestContext context,
-            IBatchDispatcher? batchDispatcher,
+            IBatchDispatcher batchDispatcher,
             IPreparedOperation operation)
         {
             if (operation.Definition.Operation == OperationType.Subscription)
@@ -129,15 +129,15 @@ internal sealed class OperationExecutionMiddleware
 
         private async Task<IQueryResult?> ExecuteQueryOrMutationAsync(
             IRequestContext context,
-            IBatchDispatcher? batchDispatcher,
+            IBatchDispatcher batchDispatcher,
             IPreparedOperation operation,
             OperationContext operationContext)
         {
             IQueryResult? result = null;
 
             if (operation.Definition.Operation == OperationType.Query)
             {
-                object? query = RootValueResolver.TryResolve(
+                object? query = RootValueResolver.Resolve(
                     context,
                     context.Services,
                     operation.RootType,
@@ -149,15 +149,15 @@ internal sealed class OperationExecutionMiddleware
                     batchDispatcher,
                     operation,
                     query,
-                    context.Variables);
+                    context.Variables!);
 
                 result = await _queryExecutor
                     .ExecuteAsync(operationContext)
                     .ConfigureAwait(false);
             }
             else if (operation.Definition.Operation == OperationType.Mutation)
             {
-                object? mutation = RootValueResolver.TryResolve(
+                object? mutation = RootValueResolver.Resolve(
                     context,
                     context.Services,
                     operation.RootType,
@@ -169,7 +169,7 @@ internal sealed class OperationExecutionMiddleware
                     batchDispatcher,
                     operation,
                     mutation,
-                    context.Variables);
+                    context.Variables!);
 
                 result = await _mutationExecutor
                     .ExecuteAsync(operationContext)

src/HotChocolate/Core/src/Execution/Processing/RootValueResolver.cs

@@ -1,36 +1,66 @@
 using System;
+using HotChocolate.Execution.Properties;
 using HotChocolate.Types;
+using static HotChocolate.Execution.Properties.Resources;
 
 namespace HotChocolate.Execution.Processing
 {
+    /// <summary>
+    /// This helper will resolve the initial value for the execution engine.
+    /// </summary>
     internal static class RootValueResolver
     {
-        public static object? TryResolve(
+        public static object? Resolve(
             IRequestContext context,
             IServiceProvider services,
             ObjectType rootType,
             ref object? cachedValue)
         {
-            if (context.Request.InitialValue is { })
+            // if an initial value was passed in with the request by the user, we will use that
+            // as root value on which the execution engine starts executing.
+            if (context.Request.InitialValue is not null)
             {
                 return context.Request.InitialValue;
             }
 
-            if (cachedValue is { })
+            // if the initial value is a singleton and was already resolved,
+            // we will use this instance.
+            if (cachedValue is not null)
             {
                 return cachedValue;
             }
 
+            // if the operation type has a proper runtime representation we will try to resolve
+            // that from the request services.
             if (rootType.RuntimeType != typeof(object))
             {
                 object? rootValue = services.GetService(rootType.RuntimeType);
 
+                // if the request services did not provide a rootValue and the runtime
+                // representation is a instantiatable class we will create a singleton ourselfs
+                // and store it as cached value in order to reuse it.
                 if (rootValue is null &&
                     !rootType.RuntimeType.IsAbstract &&
                     !rootType.RuntimeType.IsInterface)
                 {
-                    rootValue = context.Activator.CreateInstance(rootType.RuntimeType);
-                    cachedValue = rootValue;
+                    try
+                    {
+                        rootValue = context.Activator.CreateInstance(rootType.RuntimeType);
+                        cachedValue = rootValue;
+                    }
+                    catch
+                    {
+                        throw new GraphQLException(
+                            ErrorBuilder.New()
+                                .SetMessage(
+                                    RootValueResolver_Resolve_CannotCreateInstance,
+                                    rootType.Name.Value,
+                                    rootType.RuntimeType.FullName ?? rootType.RuntimeType.Name)
+                                .SetCode(ErrorCodes.Execution.CannotCreateRootValue)
+                                .SetExtension("operationType", rootType.Name)
+                                .SetExtension("runtimeType", rootType.RuntimeType.FullName)
+                                .Build());
+                    }
                 }
 
                 return rootValue;

src/HotChocolate/Core/src/Execution/Processing/SubscriptionExecutor.Subscription.cs

@@ -103,7 +103,7 @@ private async Task<IQueryResult> OnEvent(object payload)
                         ImmutableDictionary<string, object?>.Empty
                             .SetItem(WellKnownContextData.EventMessage, payload);
 
-                    object? rootValue = RootValueResolver.TryResolve(
+                    object? rootValue = RootValueResolver.Resolve(
                         _requestContext,
                         eventServices,
                         _subscriptionType,
@@ -137,7 +137,7 @@ private async ValueTask<ISourceStream> SubscribeAsync()
                 {
                     // first we will create the root value which essentially
                     // is the subscription object. In some cases this object is null.
-                    object? rootValue = RootValueResolver.TryResolve(
+                    object? rootValue = RootValueResolver.Resolve(
                         _requestContext,
                         _requestContext.Services,
                         _subscriptionType,

src/HotChocolate/Core/src/Execution/Properties/Resources.resx

@@ -243,4 +243,10 @@
   <data name="RequestExecutorBuilder_Convention_NotSuppported" xml:space="preserve">
     <value>The specified convention type is not supported.</value>
   </data>
+  <data name="RequestExecutorBuilder_Convention_NotSuppported" xml:space="preserve">
+    <value>The specified convention type is not supported.</value>
+  </data>
+  <data name="RootValueResolver_Resolve_CannotCreateInstance" xml:space="preserve">
+    <value>Unable to create the operation type `{0}` instance. Try adding the following service: `services.AddScoped&lt;{1}&gt;();`</value>
+  </data>
 </root>

src/HotChocolate/Core/test/Execution.Tests/CodeFirstTests.cs

@@ -4,7 +4,9 @@
 using System.Threading;
 using System.Threading.Tasks;
 using HotChocolate.Resolvers;
+using HotChocolate.Tests;
 using HotChocolate.Types;
+using Microsoft.Extensions.DependencyInjection;
 using Moq;
 using Snapshooter.Xunit;
 using Xunit;
@@ -263,6 +265,17 @@ public async Task ExecuteExplicitAsyncField()
             result.MatchSnapshot();
         }
 
+        [Fact]
+        public async Task CannotCreateRootValue()
+        {
+            IExecutionResult result =
+                await new ServiceCollection()
+                    .AddGraphQL()
+                    .AddQueryType<QueryPrivateConstructor>()
+                    .ExecuteRequestAsync("{ hello }")
+                    .MatchSnapshotAsync();
+        }
+
         private static Schema CreateSchema()
         {
             return Schema.Create(c =>
@@ -286,7 +299,7 @@ public string GetTest()
 
             public IExecutable<string> GetQuery()
             {
-                return new MockExecutable<string>(new []{ "foo", "bar" }.AsQueryable());
+                return new MockExecutable<string>(new[] { "foo", "bar" }.AsQueryable());
             }
 
             public string TestProp => "Hello World!";
@@ -471,7 +484,7 @@ public MockExecutable(IQueryable<T> source)
                 _source = source;
             }
 
-            public object Source =>_source;
+            public object Source => _source;
 
             public ValueTask<IList> ToListAsync(CancellationToken cancellationToken)
             {
@@ -493,5 +506,14 @@ public string Print()
                 return _source.ToString();
             }
         }
+
+        public class QueryPrivateConstructor
+        {
+            private QueryPrivateConstructor()
+            {
+            }
+
+            public string Hello() => "Hello";
+        }
     }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.CannotCreateRootValue.snap

@@ -0,0 +1,12 @@
+{
+  "errors": [
+    {
+      "message": "Unable to create the operation type \u0060QueryPrivateConstructor\u0060 instance. Try adding the following service: \u0060services.AddScoped\u003CHotChocolate.Execution.CodeFirstTests\u002BQueryPrivateConstructor\u003E();\u0060",
+      "extensions": {
+        "code": "HC0019",
+        "operationType": "QueryPrivateConstructor",
+        "runtimeType": "HotChocolate.Execution.CodeFirstTests\u002BQueryPrivateConstructor"
+      }
+    }
+  ]
+}

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteExplicitAsyncField.snap

@@ -1,16 +1,10 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "dog": {
       "names": [
         "a",
         "b"
       ]
     }
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteImplicitAsyncField.snap

@@ -1,13 +1,7 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "dog": {
       "name2": "b"
     }
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteImplicitField.snap

@@ -1,13 +1,7 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "dog": {
       "name": "a"
     }
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteImplicitFieldWithNameAttribute.snap

@@ -1,13 +1,7 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "dog": {
       "desc": "desc"
     }
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteOneFieldQueryWithMethod.snap

@@ -1,11 +1,5 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "test": "Hello World!"
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteOneFieldQueryWithProperty.snap

@@ -1,11 +1,5 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "test": "Hello World!"
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteOneFieldQueryWithQuery.snap

@@ -1,14 +1,8 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "query": [
       "foo",
       "bar"
     ]
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }

src/HotChocolate/Core/test/Execution.Tests/__snapshots__/CodeFirstTests.ExecuteWithInterface.snap

@@ -1,13 +1,7 @@
 {
-  "Label": null,
-  "Path": null,
-  "Data": {
+  "data": {
     "drink": {
       "kind": "BLACK_TEA"
     }
-  },
-  "Errors": null,
-  "Extensions": null,
-  "ContextData": null,
-  "HasNext": null
+  }
 }