Fix CompositeActivity behavior and update sample

src/core/Elsa.Abstractions/Converters/StackJsonConverter.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using Newtonsoft.Json;
+
+namespace Elsa.Converters
+{
+    /// <summary>
+    /// Correctly deserializes a <see cref="Stack{T}"/> maintaining the order of the items.
+    /// </summary>
+    public class StackJsonConverter : JsonConverter
+    {
+        public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
+        {
+            var newSerializer = new JsonSerializer();
+            newSerializer.Serialize(writer, value);
+        }
+
+        public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
+        {
+            var newSerializer = new JsonSerializer();
+            var list = newSerializer.Deserialize(reader, objectType)!;
+            return Activator.CreateInstance(objectType, list);
+        }
+
+        public override bool CanConvert(Type objectType) => objectType.IsGenericType && objectType.GetGenericTypeDefinition() == typeof(Stack<>);
+    }
+}

src/core/Elsa.Abstractions/Services/CompositeActivity.cs

@@ -21,12 +21,15 @@ namespace Elsa.Services
         {
             if (IsScheduled)
             {
+                if (HasPendingChildren(context))
+                    return PostSchedule(Id);
+
                 context.WorkflowExecutionContext.WorkflowInstance.ParentActivities.Pop();
                 IsScheduled = false;
                 return Complete(context);
             }
-            
-            var compositeActivityBlueprint = (ICompositeActivityBlueprint)context.ActivityBlueprint;
+
+            var compositeActivityBlueprint = (ICompositeActivityBlueprint) context.ActivityBlueprint;
             var startActivities = compositeActivityBlueprint.GetStartActivities().Select(x => x.Id).ToList();
             context.WorkflowExecutionContext.WorkflowInstance.ParentActivities.Push(Id);
             context.WorkflowExecutionContext.PostScheduleActivity(Id);
@@ -35,5 +38,14 @@ namespace Elsa.Services
         }
 
         protected virtual IActivityExecutionResult Complete(ActivityExecutionContext context) => Done();
+
+        private static bool HasPendingChildren(ActivityExecutionContext context)
+        {
+            var children = ((CompositeActivityBlueprint) context.ActivityBlueprint).Activities.Select(x => x.Id).ToList();
+            var workflowInstance = context.WorkflowExecutionContext.WorkflowInstance;
+            var hasPendingPostScheduledChildren = workflowInstance.PostScheduledActivities.Any(x => children.Contains(x.ActivityId));
+            var hasPendingScheduledChildren = workflowInstance.ScheduledActivities.Any(x => children.Contains(x.ActivityId));
+            return hasPendingPostScheduledChildren || hasPendingScheduledChildren;
+        }
     }
 }

src/core/Elsa.Abstractions/Services/Models/WorkflowExecutionContext.cs

@@ -97,8 +97,12 @@ namespace Elsa.Services.Models
 
         public void SchedulePostActivities()
         {
-            while (HasPostScheduledActivities)
-                ScheduleActivity(WorkflowInstance.PostScheduledActivities.Pop());
+            var activities = WorkflowInstance.PostScheduledActivities.Reverse();
+
+            foreach (var activity in activities) 
+                ScheduleActivity(activity);
+
+            WorkflowInstance.PostScheduledActivities.Clear();
         }
 
         public object? GetOutputFrom(string activityName)

src/core/Elsa.Core/Serialization/DefaultContentSerializer.cs

@@ -46,6 +46,7 @@ namespace Elsa.Serialization
             settings.Converters.Add(new StringEnumConverter(new DefaultNamingStrategy()));
             settings.Converters.Add(new TypeJsonConverter());
             settings.Converters.Add(new VersionOptionsJsonConverter());
+            settings.Converters.Add(new StackJsonConverter());
         }
 
         public static JsonSerializerSettings CreateDefaultJsonSerializationSettings()

src/persistence/Elsa.Persistence.YesSql/CustomJsonContentSerializer.cs

@@ -1,6 +1,7 @@
 using System;
-
+using Elsa.Converters;
 using Newtonsoft.Json;
+using Newtonsoft.Json.Converters;
 using Newtonsoft.Json.Serialization;
 
 using NodaTime;
@@ -19,7 +20,13 @@ namespace Elsa.Persistence.YesSql
             JsonSettings = new JsonSerializerSettings
             {
                 TypeNameHandling = TypeNameHandling.Auto
-            }.ConfigureForNodaTime(DateTimeZoneProviders.Tzdb);
+            };
+            
+            JsonSettings.ConfigureForNodaTime(DateTimeZoneProviders.Tzdb);
+            JsonSettings.Converters.Add(new StackJsonConverter());
+            JsonSettings.Converters.Add(new VersionOptionsJsonConverter());
+            JsonSettings.Converters.Add(new TypeJsonConverter());
+            JsonSettings.Converters.Add(new StringEnumConverter(new DefaultNamingStrategy()));
 
             JsonSettings.ContractResolver = new DefaultContractResolver
             {

src/samples/worker/Elsa.Samples.WhileLoopWorker/Activities/MakePhoneCall.cs

@@ -0,0 +1,34 @@
+using Elsa.Activities.Console;
+using Elsa.Activities.ControlFlow;
+using Elsa.Activities.Timers;
+using Elsa.Builders;
+using Elsa.Samples.WhileLoopWorker.Services;
+using Elsa.Services;
+using NodaTime;
+
+namespace Elsa.Samples.WhileLoopWorker.Activities
+{
+    public class MakePhoneCall : CompositeActivity
+    {
+        private readonly PhoneCallService _phoneCallService;
+
+        public MakePhoneCall(PhoneCallService phoneCallService)
+        {
+            _phoneCallService = phoneCallService;
+        }
+
+        public override void Build(ICompositeActivityBuilder composite)
+        {
+            composite
+                .While(() => _phoneCallService.CallStatus != PhoneCallStatus.Finished,
+                    @while =>
+                    {
+                        @while
+                            .WriteLine("Ringgggg ringgg.")
+                            .Timer(Duration.FromSeconds(5))
+                            .Then(() => _phoneCallService.Progress())
+                            .WriteLine(() => $"Call status: {_phoneCallService.CallStatus}");
+                    });
+        }
+    }
+}

src/samples/worker/Elsa.Samples.WhileLoopWorker/Elsa.Samples.WhileLoopWorker.csproj

@@ -6,10 +6,11 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0"/>
+        <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0" />
     </ItemGroup>
 
     <ItemGroup>
-        <ProjectReference Include="..\..\..\core\Elsa\Elsa.csproj"/>
+        <ProjectReference Include="..\..\..\core\Elsa\Elsa.csproj" />
+        <ProjectReference Include="..\..\..\persistence\Elsa.Persistence.YesSql\Elsa.Persistence.YesSql.csproj" />
     </ItemGroup>
 </Project>

src/samples/worker/Elsa.Samples.WhileLoopWorker/Program.cs

@@ -3,6 +3,8 @@ using Elsa.Samples.WhileLoopWorker.Workflows;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Elsa.Persistence.InMemory;
+using Elsa.Persistence.YesSql.Extensions;
+using Elsa.Samples.WhileLoopWorker.Activities;
 
 namespace Elsa.Samples.WhileLoopWorker
 {
@@ -16,11 +18,12 @@ namespace Elsa.Samples.WhileLoopWorker
                     (_, services) =>
                     {
                         services
-                            .AddElsa()
+                            .AddElsa(options => options.UseYesSqlPersistence())
                             .AddConsoleActivities()
                             .AddTimerActivities()
                             .AddSingleton<PhoneCallService>()
                             .AddHostedService<PhoneCallWorker>()
+                            .AddActivity<MakePhoneCall>()
                             .AddWorkflow<PhoneCallWorkflow>();
                     });
     }

src/samples/worker/Elsa.Samples.WhileLoopWorker/Workflows/PhoneCallWorkflow.cs

@@ -1,9 +1,7 @@
 using Elsa.Activities.Console;
-using Elsa.Activities.ControlFlow;
-using Elsa.Activities.Timers;
 using Elsa.Builders;
+using Elsa.Samples.WhileLoopWorker.Activities;
 using Elsa.Samples.WhileLoopWorker.Services;
-using NodaTime;
 
 namespace Elsa.Samples.WhileLoopWorker.Workflows
 {
@@ -23,18 +21,8 @@ namespace Elsa.Samples.WhileLoopWorker.Workflows
         public void Build(IWorkflowBuilder workflow)
         {
             workflow
-                .WriteLine("Simulating a phone call... ringgg ringgg.")
-                .While(() => _phoneCallService.CallStatus != PhoneCallStatus.Finished,
-                    @while =>
-                    {
-                        @while
-                            .WriteLine("Ringgggg ringgg.")
-                            .WriteLine(() => $"Call status: {_phoneCallService.CallStatus}")
-                            .Timer(Duration.FromSeconds(5))
-                            .Then(() => _phoneCallService.Progress());
-
-                    })
-                .WriteLine(() => $"Call status: {_phoneCallService.CallStatus}")
+                .WriteLine("Simulating a phone call...")
+                .Then<MakePhoneCall>()
                 .WriteLine("Workflow finished.");
         }
     }