Add TGrainState type constraints to document necessary system constraints - Resolves #1906

src/Orleans/Core/Grain.cs

@@ -6,6 +6,7 @@
 using System.Threading.Tasks;
 using Orleans.Core;
 using Orleans.Runtime;
+using Orleans.Storage;
 using Orleans.Streams;
 
 namespace Orleans
@@ -247,7 +248,7 @@ internal string CaptureRuntimeEnvironment()
     /// Base class for a Grain with declared persistent state.
     /// </summary>
     /// <typeparam name="TGrainState">The class of the persistent state object</typeparam>
-    public class Grain<TGrainState> : Grain, IStatefulGrain
+    public class Grain<TGrainState> : Grain, IStatefulGrain where TGrainState : new()
     {
         private readonly GrainState<TGrainState> grainState;
 

src/OrleansEventSourcing/JournaledGrain.cs

@@ -8,7 +8,7 @@ namespace Orleans.EventSourcing
     /// The base class for all grain classes that have event-sourced state.
     /// </summary>
     public class JournaledGrain<TGrainState> : Grain<TGrainState>
-        where TGrainState : JournaledGrainState<TGrainState>
+        where TGrainState : JournaledGrainState<TGrainState>, new()
     {
         /// <summary>
         /// Helper method for raising events, applying them to TGrainState and optionally committing to storage

src/OrleansEventSourcing/JournaledGrainState.cs

@@ -9,7 +9,7 @@ namespace Orleans.EventSourcing
     /// Base class for event-sourced grain state classes.
     /// </summary>
     public abstract class JournaledGrainState<TGrainState>
-        where TGrainState : JournaledGrainState<TGrainState>
+        where TGrainState : JournaledGrainState<TGrainState>, new()
     {
         private List<object> events = new List<object>();
         protected TGrainState State;

src/OrleansRuntime/GrainTypeManager/SiloAssemblyLoader.cs

@@ -92,7 +92,7 @@ public IDictionary<string, GrainTypeData> GetGrainClassTypes(bool strict)
                         if (definition == typeof(Grain<>))
                         {
                             var stateArg = parentType.GetGenericArguments()[0];
-                            if (stateArg.GetTypeInfo().IsClass)
+                            if (stateArg.GetTypeInfo().IsClass || stateArg.GetTypeInfo().IsValueType)
                             {
                                 grainStateType = stateArg;
                                 break;

test/TestGrainInterfaces/IValueTypeTestGrain.cs

@@ -122,13 +122,11 @@ public void SetT(T t)
         }
     }
 
-    public interface IValueTypeTestGrain : IGrainWithIntegerKey
+    public interface IValueTypeTestGrain : IGrainWithGuidKey
     {
         Task<ValueTypeTestData> GetStateData();
 
         Task SetStateData(ValueTypeTestData d);
-
-        Task<CampaignEnemyTestType> GetEnemyType();
     }
 
     public interface IEnumResultGrain : IGrainWithIntegerKey

test/TestGrains/ValueTypeTestGrain.cs

@@ -4,40 +4,23 @@
 
 namespace UnitTests.Grains
 {
-    public class ValueTypeTestGrainState
-    {
-        public ValueTypeTestData StateData { get; set; }
-    }
-
     [Orleans.Providers.StorageProvider(ProviderName = "MemoryStore")]
-    public class ValueTypeTestGrain : Grain<ValueTypeTestGrainState>, IValueTypeTestGrain
+    public class ValueTypeTestGrain : Grain<ValueTypeTestData>, IValueTypeTestGrain
     {
         public ValueTypeTestGrain()
         {
-            State.StateData = new ValueTypeTestData(7);
-        }
-
-        public Task SetState(ValueTypeTestData d)
-        {
-            State.StateData = d;
-            return TaskDone.Done;
         }
 
-        public Task<CampaignEnemyTestType> GetEnemyType()
+        public async Task<ValueTypeTestData> GetStateData()
         {
-            return Task.FromResult(CampaignEnemyTestType.Enemy2);
+            await ReadStateAsync();
+            return State;
         }
 
-        public Task<ValueTypeTestData> GetStateData()
-        {
-            return Task.FromResult(State.StateData);
-        }
-
-
         public Task SetStateData(ValueTypeTestData d)
         {
-            State.StateData = d;
-            return TaskDone.Done;
+            State = d;
+            return WriteStateAsync();
         }
     }
 }

test/Tester/GenericGrainTests.cs

@@ -678,6 +678,22 @@ public async Task Generic_GrainWithTypeConstraints()
             Assert.Equal(1, result);
         }
 
+        [Fact, TestCategory("Functional"), TestCategory("Persistence")]
+        public async Task Generic_GrainWithValueTypeState()
+        {
+            Guid id = Guid.NewGuid();
+            var grain = GrainClient.GrainFactory.GetGrain<IValueTypeTestGrain>(id);
+
+            var initial = await grain.GetStateData();
+            Assert.Equal(new ValueTypeTestData(0), initial);
+
+            var expectedValue = new ValueTypeTestData(42);
+
+            await grain.SetStateData(expectedValue);
+
+            Assert.Equal(expectedValue, await grain.GetStateData());
+        }
+
         [Fact(Skip = "https://github.com/dotnet/orleans/issues/1655 Casting from non-generic to generic interface fails with an obscure error message"), TestCategory("Functional"), TestCategory("Cast"), TestCategory("Generics")]
         public async Task Generic_CastToGenericInterfaceAfterActivation() 
         {

test/TesterInternal/StorageTests/Relational/TestDataSets/GrainTypeGenerator.cs

@@ -18,23 +18,16 @@ private interface ITestGrainWithIntegerKey: IGrainWithIntegerKey { }
         private interface ITestGrainGenericWithIntegerKey<T>: IGrainWithIntegerKey { }
         private class TestGrainWithIntegerKey: Grain, ITestGrainWithIntegerKey { }
         private class TestGrainGenericWithIntegerKey<T>: Grain, ITestGrainGenericWithIntegerKey<T> { }
-        private class TestGrainStateWithIntegerKey<TState>: Grain<TState>, ITestGrainWithIntegerKey { }
-        private class TestGrainStateGenericWithIntegerKey<T, TState>: Grain<TState>, ITestGrainGenericWithIntegerKey<T> { }
 
         private interface ITestGrainWithGuidKey: IGrainWithGuidKey { }
         private interface ITestGrainGenericWithGuidKey<T>: IGrainWithGuidKey { }
         private class TestGrainWithGuidKey: Grain, ITestGrainWithGuidKey { }
         private class TestGrainGenericWithGuidKey<T>: Grain, ITestGrainGenericWithGuidKey<T> { }
-        private class TestGrainStateWithGuidKey<TState>: Grain<TState>, ITestGrainWithGuidKey { }
-        private class TestGrainStateGenericWithGuidKey<T, TState>: Grain<TState>, ITestGrainGenericWithGuidKey<T> { }
 
         private interface ITestGrainWithStringKey: IGrainWithStringKey { }
         private interface ITestGrainGenericWithStringKey<T>: IGrainWithStringKey { }
         private class TestGrainWithStringKey: Grain, ITestGrainWithStringKey { }
         private class TestGrainGenericWithStringKey<T>: Grain, ITestGrainGenericWithStringKey<T> { }
-        private class TestGrainStateWithStringKey<TState>: Grain<TState>, ITestGrainWithStringKey { }
-        private class TestGrainStateGenericWithStringKey<T, TState>: Grain<TState>, ITestGrainGenericWithStringKey<T> { }
-
 
         private static Dictionary<Type, Func<Type, Type, Type>> GrainTypeSwitch { get; } = new Dictionary<Type, Func<Type, Type, Type>>
         {