Add delete implicit operation (#178)

src/Abstractions/Entities/TaskEntity.cs

@@ -72,6 +72,14 @@ public interface ITaskEntity
 /// Entity state will be hydrated into the <see cref="TaskEntity{TState}.State"/> property. See <see cref="State"/> for
 /// more information.
 /// </para>
+///
+/// <para><b>Implicit Operations</b></para>
+/// <para>
+/// This class supports some operations implicitly. Implicit operations have the lowest priority, after entity and state
+/// method dispatching. To override an implicit operation, implement a public method of the same name. Throw
+/// <see cref="NotSupportedException"/> from the method to indicate the implicit operation is not supported at all.
+/// </para>
+/// <para><c>delete</c>: deletes the entity state from storage.</para>
 /// </remarks>
 public abstract class TaskEntity<TState> : ITaskEntity
 {
@@ -120,6 +128,12 @@ public abstract class TaskEntity<TState> : ITaskEntity
         if (!operation.TryDispatch(this, out object? result, out Type returnType)
             && !this.TryDispatchState(operation, out result, out returnType))
         {
+            if (TryDispatchImplicit(operation, out ValueTask<object?> task))
+            {
+                // We do not go into UnwrapAsync for implicit tasks
+                return task;
+            }
+
             throw new NotSupportedException($"No suitable method found for entity operation '{operation}'.");
         }
 
@@ -144,6 +158,20 @@ protected virtual TState InitializeState()
         return Activator.CreateInstance<TState>();
     }
 
+    static bool TryDispatchImplicit(TaskEntityOperation operation, out ValueTask<object?> result)
+    {
+        // We do not implement implicit operations via methods because then they would supersede state-dispatching.
+        // As such, implicit operations are manually implemented here.
+        result = default;
+        if (string.Equals(operation.Name, "delete", StringComparison.OrdinalIgnoreCase))
+        {
+            operation.State.SetState(null);
+            return true;
+        }
+
+        return false;
+    }
+
     bool TryDispatchState(TaskEntityOperation operation, out object? result, out Type returnType)
     {
         if (!this.AllowStateDispatch)

test/Abstractions.Tests/Entities/EntityTaskEntityTests.cs

@@ -125,6 +125,34 @@ public async Task DefaultValue_Input_Succeeds()
         result.Should().BeOfType<string>().Which.Should().Be("not-default");
     }
 
+    [Theory]
+    [InlineData("delete")]
+    [InlineData("Delete")]
+    public async Task ImplicitDelete_ClearsState(string op)
+    {
+        TestEntityOperation operation = new(op, 10, default);
+        TestEntity entity = new();
+
+        object? result = await entity.RunAsync(operation);
+
+        result.Should().BeNull();
+        operation.State.GetState(typeof(object)).Should().BeNull();
+    }
+
+    [Theory]
+    [InlineData("delete")]
+    [InlineData("Delete")]
+    public async Task ExplicitDelete_Overridden(string op)
+    {
+        TestEntityOperation operation = new(op, 10, default);
+        DeleteEntity entity = new();
+
+        object? result = await entity.RunAsync(operation);
+
+        result.Should().BeNull();
+        operation.State.GetState(typeof(int)).Should().Be(0);
+    }
+
 #pragma warning disable CA1822 // Mark members as static
 #pragma warning disable IDE0060 // Remove unused parameter
     class TestEntity : TaskEntity<int>
@@ -215,6 +243,11 @@ int Get(Optional<TaskEntityContext> context)
             return this.State;
         }
     }
+
+    class DeleteEntity : TaskEntity<int>
+    {
+        public void Delete() => this.State = 0;
+    }
 #pragma warning restore IDE0060 // Remove unused parameter
 #pragma warning restore CA1822 // Mark members as static
 }

test/Abstractions.Tests/Entities/StateTaskEntityTests.cs

@@ -158,6 +158,20 @@ public async Task DefaultValue_Input_Succeeds()
         result.Should().BeOfType<string>().Which.Should().Be("not-default");
     }
 
+    [Theory]
+    [InlineData("delete")]
+    [InlineData("Delete")]
+    public async Task ExplicitDelete_Overridden(string op)
+    {
+        TestEntityOperation operation = new(op, State(10), default);
+        TestEntity entity = new();
+
+        object? result = await entity.RunAsync(operation);
+
+        result.Should().BeNull();
+        operation.State.GetState(typeof(TestState)).Should().BeOfType<TestState>().Which.Value.Should().Be(0);
+    }
+
     static TestState State(int value) => new() { Value = value };
 
     class NullStateEntity : TestEntity
@@ -187,6 +201,8 @@ class TestState
 
         public static string StaticMethod() => throw new NotImplementedException();
 
+        public void Delete() => this.Value = 0;
+
         public int Precedence() => 10;
 
         public int Add0(int value) => this.Add(value, default);