From 43cfe431f1b116a76735496268c523ca2e04266d Mon Sep 17 00:00:00 2001
From: Sipke Schoorstra <sipkeschoorstra@outlook.com>
Date: Thu, 3 Dec 2020 19:49:12 +0100
Subject: [PATCH] Make descriptor building resilient

---
 .../Services/Models/ActivityBlueprintWrapper.cs     | 13 +++++++++++--
 .../Services/Models/IActivityBlueprintWrapper.cs    |  2 +-
 .../Activities/CountDownActivity.cs                 |  5 ++++-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/core/Elsa.Abstractions/Services/Models/ActivityBlueprintWrapper.cs b/src/core/Elsa.Abstractions/Services/Models/ActivityBlueprintWrapper.cs
index b8b37102a..0e9c71c8d 100644
--- a/src/core/Elsa.Abstractions/Services/Models/ActivityBlueprintWrapper.cs
+++ b/src/core/Elsa.Abstractions/Services/Models/ActivityBlueprintWrapper.cs
@@ -25,11 +25,20 @@ namespace Elsa.Services.Models
         {
         }
 
-        public async ValueTask<T> GetPropertyValueAsync<T>(Expression<Func<TActivity, T>> propertyExpression, CancellationToken cancellationToken = default)
+        public async ValueTask<T?> GetPropertyValueAsync<T>(Expression<Func<TActivity, T>> propertyExpression, CancellationToken cancellationToken = default)
         {
             var workflowBlueprint = ActivityExecutionContext.WorkflowExecutionContext.WorkflowBlueprint;
             var activityId = ActivityExecutionContext.ActivityBlueprint.Id;
-            return await workflowBlueprint.GetActivityPropertyValue(activityId, propertyExpression, ActivityExecutionContext, cancellationToken);
+
+            // Computed property setters that depend on actual workflow state might fault, since we are using a fake activity execution context.
+            try
+            {
+                return await workflowBlueprint.GetActivityPropertyValue(activityId, propertyExpression, ActivityExecutionContext, cancellationToken);
+            }
+            catch (Exception e)
+            {
+                return default;
+            }
         }
 
         public T? GetState<T>(Expression<Func<TActivity, T>> propertyExpression)
diff --git a/src/core/Elsa.Abstractions/Services/Models/IActivityBlueprintWrapper.cs b/src/core/Elsa.Abstractions/Services/Models/IActivityBlueprintWrapper.cs
index d404d57ce..271f9f518 100644
--- a/src/core/Elsa.Abstractions/Services/Models/IActivityBlueprintWrapper.cs
+++ b/src/core/Elsa.Abstractions/Services/Models/IActivityBlueprintWrapper.cs
@@ -13,7 +13,7 @@ namespace Elsa.Services.Models
 
     public interface IActivityBlueprintWrapper<TActivity> : IActivityBlueprintWrapper where TActivity:IActivity
     {
-        ValueTask<T> GetPropertyValueAsync<T>(Expression<Func<TActivity, T>> propertyExpression, CancellationToken cancellationToken = default);
+        ValueTask<T?> GetPropertyValueAsync<T>(Expression<Func<TActivity, T>> propertyExpression, CancellationToken cancellationToken = default);
         T? GetState<T>(Expression<Func<TActivity, T>> propertyExpression);
     }
 }
\ No newline at end of file
diff --git a/src/samples/console/Elsa.Samples.ProgrammaticCompositeActivitiesConsole/Activities/CountDownActivity.cs b/src/samples/console/Elsa.Samples.ProgrammaticCompositeActivitiesConsole/Activities/CountDownActivity.cs
index 33ab80ab5..c7cb8427c 100644
--- a/src/samples/console/Elsa.Samples.ProgrammaticCompositeActivitiesConsole/Activities/CountDownActivity.cs
+++ b/src/samples/console/Elsa.Samples.ProgrammaticCompositeActivitiesConsole/Activities/CountDownActivity.cs
@@ -17,11 +17,14 @@ namespace Elsa.Samples.ProgrammaticCompositeActivitiesConsole.Activities
         public override void Build(ICompositeActivityBuilder composite)
         {
             composite
-                .WriteLine("Turn left or right?")
+                .StartWith(GetInstructions)
+                .WriteLine(context => (string)context.Input)
                 .ReadLine()
                 .Finish(context => (string) context.Input);
         }
 
         protected override IActivityExecutionResult Complete(ActivityExecutionContext context) => Outcome(((string) context.WorkflowExecutionContext.WorkflowInstance.Output)!);
+        
+        private static void GetInstructions(ActivityExecutionContext context) => context.Output = "Turn left or right?";
     }
 }
\ No newline at end of file