Improve variable vs non-variable persistence (#3568)

* Incremental fixes

* Fix base assignment of async delegate block reference

* Reuse existing memory blocks

* Remove PlaybackStarted child activity

The PlaybackStarted property is unnecessary, since the PlayAudio activity already completes right after playback has started.

* Add GetCallStatus API method

* Prevent variables on composite activities to be overwritten during deserialization

* Remove unnecessary variable declarations

Activity variables will be declared automatically during activity invocation.

* Add XML comments

* Remove unused references arg

* Streamline variable identity assignment

* Fix composite early exit completion

* Move identity assignment to workflow definition service

src/designer/elsa-workflows-designer/src/components/designer/variables-editor/variable-editor-dialog-content.tsx

@@ -55,11 +55,11 @@ export class VariableEditorDialogContent {
               </FormEntry>
 
               <FormEntry fieldId="variableStorageDriverId" label="Storage" hint="The storage to use when persisting the variable.">
-                <select id="variableStorageDriverId" name="variableStorageDriverId">
+                <select id="variableStorageDriverTypeName" name="variableStorageDriverTypeName">
                   {storageDrivers.map(driver => {
-                    const value = driver.id;
+                    const value = driver.typeName;
                     const text = driver.displayName;
-                    const selected = value == variable.storageDriverId;
+                    const selected = value == variable.storageDriverTypeName;
                     return <option value={value} selected={selected}>{text}</option>;
                   })}
                 </select>
@@ -84,13 +84,13 @@ export class VariableEditorDialogContent {
     const name = formData.get('variableName') as string;
     const value = formData.get('variableValue') as string;
     const type = formData.get('variableTypeName') as string;
-    const driverId = formData.get('variableStorageDriverId') as string;
+    const driverTypeName = formData.get('variableStorageDriverTypeName') as string;
     const variable = this.variable;
 
     variable.name = name;
     variable.typeName = type;
     variable.value = value;
-    variable.storageDriverId = isNullOrWhitespace(driverId) ? null : driverId;
+    variable.storageDriverTypeName = isNullOrWhitespace(driverTypeName) ? null : driverTypeName;
 
     return variable;
   };

src/designer/elsa-workflows-designer/src/components/designer/variables-editor/variables-editor.tsx

@@ -60,7 +60,7 @@ export class VariablesEditor {
             </thead>
             <tbody>
             {variables.map(variable => {
-                const storage = storageDrivers.find(x => x.id == variable.storageDriverId);
+                const storage = storageDrivers.find(x => x.typeName == variable.storageDriverTypeName);
                 const storageName = storage?.displayName ?? '-';
                 const descriptor = descriptorsStore.variableDescriptors.find(x => x.typeName == variable.typeName);
                 const typeDisplayName = descriptor?.displayName ?? variable.typeName;

src/designer/elsa-workflows-designer/src/models/api.ts

@@ -72,7 +72,7 @@ export interface IntellisenseContext {
 }
 
 export interface StorageDriverDescriptor {
-  id: string;
+  typeName: string;
   displayName: string;
 }
 

src/designer/elsa-workflows-designer/src/models/core.ts

@@ -34,7 +34,7 @@ export interface Variable {
   name: string;
   typeName: string;
   value?: any;
-  storageDriverId?: string;
+  storageDriverTypeName?: string;
 }
 
 export interface ActivityInput {

src/modules/Elsa.Dsl/Interpreters/WorkflowDefinitionBuilderInterpreter/WorkflowDefinitionBuilderInterpreter.cs

@@ -2,6 +2,7 @@
 using Elsa.Dsl.Models;
 using Elsa.Dsl.Services;
 using Elsa.Expressions.Services;
+using Elsa.Workflows.Core.Activities;
 using Elsa.Workflows.Core.Services;
 
 namespace Elsa.Dsl.Interpreters;
@@ -17,8 +18,9 @@ public partial class WorkflowDefinitionBuilderInterpreter : ElsaParserBaseVisito
     private readonly ParseTreeProperty<IList<object?>> _argValues = new();
     private readonly ParseTreeProperty<Type> _expressionType = new();
     private readonly IDictionary<string, DefinedVariable> _definedVariables = new Dictionary<string, DefinedVariable>();
-    private readonly Stack<IContainer> _containerStack = new();
+    private readonly Stack<Container> _containerStack = new();
 
+    /// <inheritdoc />
     public WorkflowDefinitionBuilderInterpreter(
         ITypeSystem typeSystem, 
         IFunctionActivityRegistry functionActivityRegistry, 

src/modules/Elsa.Expressions/Elsa.Expressions.csproj

@@ -13,7 +13,6 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="Dahomey.Json" Version="1.12.2" />
       <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="7.0.0" />
       <PackageReference Include="Microsoft.Extensions.Options" Version="7.0.0" />
     </ItemGroup>

src/modules/Elsa.Expressions/Extensions/TypeExtensions.cs

@@ -0,0 +1,12 @@
+namespace Elsa.Expressions.Extensions;
+
+/// <summary>
+/// Adds extension methods to <see cref="Type"/>.
+/// </summary>
+public static class TypeExtensions
+{
+    /// <summary>
+    /// Returns the default value for the specified type.
+    /// </summary>
+    public static object? GetDefaultValue(this Type type) => type.IsClass ? null : Activator.CreateInstance(type);
+}

src/modules/Elsa.Expressions/Helpers/ObjectConverter.cs

@@ -1,17 +1,32 @@
 using System.ComponentModel;
-using System.Runtime.CompilerServices;
 using System.Text.Json;
 using System.Text.Json.Serialization;
-using Dahomey.Json;
-using Dahomey.Json.Serialization.Conventions;
-using Dahomey.Json.Util;
 using Elsa.Expressions.Exceptions;
-using DahomeyJsonNode = System.Text.Json.JsonNode;
+using Elsa.Expressions.Extensions;
+using Elsa.Expressions.Models;
 
 namespace Elsa.Expressions.Helpers;
 
+/// <summary>
+/// A helper that attempts many strategies to try and convert the source value into the destination type. 
+/// </summary>
 public static class ObjectConverter
 {
+    public static Result TryConvertTo<T>(this object? value, JsonSerializerOptions? serializerOptions = null) => value.TryConvertTo(typeof(T), serializerOptions);
+    
+    public static Result TryConvertTo(this object? value, Type targetType, JsonSerializerOptions? serializerOptions = null)
+    {
+        try
+        {
+            var convertedValue = value.ConvertTo(targetType, serializerOptions);
+            return new Result(true, convertedValue, null);
+        }
+        catch (Exception e)
+        {
+            return new Result(false, null, e);
+        }
+    }
+
     public static T? ConvertTo<T>(this object? value, JsonSerializerOptions? serializerOptions = null) => value != null ? (T?)value.ConvertTo(typeof(T), serializerOptions) : default;
 
     public static object? ConvertTo(this object? value, Type targetType, JsonSerializerOptions? serializerOptions = null)
@@ -32,9 +47,6 @@ public static class ObjectConverter
 
         var underlyingTargetType = Nullable.GetUnderlyingType(targetType) ?? targetType;
 
-        if (value is DahomeyJsonNode { ValueKind: JsonValueKind.Object } dahomyJsonObject)
-            return ToObject(dahomyJsonObject, targetType, options);
-
         if (value is JsonElement jsonNumber && jsonNumber.ValueKind == JsonValueKind.Number && underlyingTargetType == typeof(string))
             return jsonNumber.ToString().ConvertTo(underlyingTargetType);
 
@@ -42,7 +54,7 @@ public static class ObjectConverter
         {
             if (jsonObject.ValueKind == JsonValueKind.String && underlyingTargetType != typeof(string))
                 return jsonObject.GetString().ConvertTo(underlyingTargetType);
-            
+
             return jsonObject.Deserialize(targetType, options);
         }
 
@@ -108,10 +120,4 @@ public static class ObjectConverter
             throw new TypeConversionException($"Failed to convert an object of type {sourceType} to {underlyingTargetType}", value, underlyingTargetType, e);
         }
     }
-
-    private static object? ToObject(this DahomeyJsonNode node, Type type, JsonSerializerOptions? options = null)
-    {
-        using var arrayBufferWriter = new ArrayBufferWriter<byte>();
-        return JsonSerializer.Deserialize(node.ToString(), type, options);
-    }
 }

src/modules/Elsa.Expressions/Models/DelegateBlockReference.cs

@@ -32,7 +32,7 @@ public class DelegateBlockReference<T> : DelegateBlockReference
     {
     }
         
-    public DelegateBlockReference(Func<ExpressionExecutionContext, ValueTask<T?>> @delegate) : base(x => @delegate(x))
+    public DelegateBlockReference(Func<ExpressionExecutionContext, ValueTask<T?>> @delegate) : base(async x => await @delegate(x))
     {
     }
 }

src/modules/Elsa.Expressions/Models/MemoryRegister.cs

@@ -38,7 +38,10 @@ public class MemoryRegister
 
     public MemoryBlock Declare(MemoryBlockReference blockReference)
     {
-        var block = blockReference.Declare();
+        if (TryGetBlock(blockReference.Id, out var block))
+            return block;
+
+        block = blockReference.Declare();
         Blocks[blockReference.Id] = block;
         return block;
     }

src/modules/Elsa.Expressions/Models/Result.cs

@@ -0,0 +1,51 @@
+namespace Elsa.Expressions.Models;
+
+/// <summary>
+/// A simple monad that runs either the <see cref="OnSuccess"/> or <see cref="OnFailure"/> lambda, depending on whether or not the operation succeeded.
+/// </summary>
+public class Result
+{
+    internal Result(bool success, object? value, Exception? exception)
+    {
+        Success = success;
+        Value = value;
+        Exception = exception;
+    }
+
+    /// <summary>
+    /// True if the conversaion succeeded, false otherwise.
+    /// </summary>
+    public bool Success { get; }
+    
+    /// <summary>
+    /// The result value.
+    /// </summary>
+    public object? Value { get; }
+    
+    /// <summary>
+    /// Any exception that may have occurred during the operation.
+    /// </summary>
+    public Exception? Exception { get; }
+
+    /// <summary>
+    /// Runs the provided delegate if the result is successful.
+    /// </summary>
+    public Result OnSuccess(Action<object?> successHandler)
+    {
+        if (Success)
+            successHandler(Value);
+
+        return this;
+    }
+
+    /// <summary>
+    /// Runs the provided delegate if the result is unsuccessful.
+    /// </summary>
+    public Result OnFailure(Action<Exception> failureHandler)
+    {
+        if (Exception != null)
+            failureHandler(Exception);
+
+        return this;
+    }
+}

src/modules/Elsa.Telnyx/Activities/PlayAudio.cs

@@ -42,12 +42,6 @@ public class PlayAudio : PlayAudioBase
     {
     }
 
-    /// <summary>
-    /// The <see cref="IActivity"/> to execute when audio playback has started.
-    /// </summary>
-    [Port]
-    public IActivity? PlaybackStarted { get; set; }
-
     /// <summary>
     /// The <see cref="IActivity"/> to execute when the call was no longer active.
     /// </summary>
@@ -55,7 +49,7 @@ public class PlayAudio : PlayAudioBase
     public IActivity? Disconnected { get; set; }
 
     /// <inheritdoc />
-    protected override async ValueTask HandlePlaybackStartedAsync(ActivityExecutionContext context) => await context.ScheduleActivityAsync(PlaybackStarted, OnCompletedAsync);
+    protected override async ValueTask HandlePlaybackStartedAsync(ActivityExecutionContext context) => await context.CompleteActivityAsync();
 
     /// <inheritdoc />
     protected override async ValueTask HandleDisconnectedAsync(ActivityExecutionContext context) => await context.ScheduleActivityAsync(Disconnected, OnCompletedAsync);

src/modules/Elsa.Telnyx/Client/Models/Responses.cs

@@ -5,6 +5,15 @@ namespace Elsa.Telnyx.Client.Models;
 
 public record TelnyxResponse<T>(T Data);
 
+public record CallStatusResponse(
+    string CallControlId,
+    string CallLegId,
+    string CallSessionId,
+    string ClientState,
+    bool IsAlive,
+    string RecordType
+);
+
 public record DialResponse(
     string CallControlId,
     string CallLegId,

src/modules/Elsa.Telnyx/Client/Services/ICallsApi.cs

@@ -5,6 +5,9 @@ namespace Elsa.Telnyx.Client.Services;
 
 public interface ICallsApi
 {
+    [Get("/v2/calls/{callControlId}")]
+    Task<TelnyxResponse<CallStatusResponse>> GetStatusAsync(string callControlId, CancellationToken cancellationToken = default);
+    
     [Post("/v2/calls")]
     Task<TelnyxResponse<DialResponse>> DialAsync([Body] DialRequest request, CancellationToken cancellationToken = default);
 

src/modules/Elsa.Workflows.Api/Endpoints/StorageDrivers/List/Models.cs

@@ -10,4 +10,4 @@ public class Response
     public ICollection<StorageDriverDescriptor> Items  { get; set; }
 }
 
-public record StorageDriverDescriptor(string Id, string DisplayName);
+public record StorageDriverDescriptor(string TypeName, string DisplayName);

src/modules/Elsa.Workflows.Core/Activities/Composite.cs

@@ -22,6 +22,7 @@ public abstract class Composite : ActivityBase, IVariableContainer
     }
 
     /// <inheritdoc />
+    [JsonIgnore]  // Composite activities' Variables is intended to be constructed from code only.
     public ICollection<Variable> Variables { get; init; } = new List<Variable>();
     
     /// <summary>
@@ -29,7 +30,7 @@ public abstract class Composite : ActivityBase, IVariableContainer
     /// </summary>
     [Port]
     [Browsable(false)]
-    [JsonIgnore] // Composite activities' Root is intended to be constructed from code only, so we don't want to get it serialized.
+    [JsonIgnore] // Composite activities' Root is intended to be constructed from code only.
     public IActivity Root { get; set; } = new Sequence();
 
     /// <inheritdoc />
@@ -74,12 +75,15 @@ public abstract class Composite : ActivityBase, IVariableContainer
     
     private async ValueTask OnCompleteCompositeSignal(CompleteCompositeSignal signal, SignalContext context)
     {
+        await OnCompletedAsync(context.ReceiverActivityExecutionContext, context.SenderActivityExecutionContext);
+        
         // Complete the sender first so that it notifies its parents to complete.
         await context.SenderActivityExecutionContext.CompleteActivityAsync();
         
         // Then complete this activity.
         await context.ReceiverActivityExecutionContext.CompleteActivityAsync(signal.Result);
         context.StopPropagation();
+        
     }
 
     /// <summary>

src/modules/Elsa.Workflows.Core/Activities/Container.cs

@@ -28,9 +28,6 @@ public abstract class Container : ActivityBase, IVariableContainer
     /// <inheritdoc />
     protected override async ValueTask ExecuteAsync(ActivityExecutionContext context)
     {
-        // Register variables.
-        context.ExpressionExecutionContext.Memory.Declare(Variables);
-
         // Schedule children.
         await ScheduleChildrenAsync(context);
     }

src/modules/Elsa.Workflows.Core/Extensions/ActivityExecutionContextExtensions.cs

@@ -103,6 +103,9 @@ public static class ActivityExecutionContextExtensions
         context.SetHasEvaluatedProperties();
     }
 
+    /// <summary>
+    /// Evaluates the specified input property of the activity.
+    /// </summary>
     public static async Task<T?> EvaluateInputPropertyAsync<TActivity, T>(this ActivityExecutionContext context, Expression<Func<TActivity, Input<T>>> propertyExpression)
     {
         var inputName = propertyExpression.GetProperty()!.Name;

src/modules/Elsa.Workflows.Core/Extensions/ActivityExtensions.cs

@@ -43,15 +43,16 @@ public static class ActivityExtensions
         return query.Select(x => x!).ToList();
     }
 
-    public static IEnumerable<Variable> GetVariables(this IActivity activity)
+    public static IEnumerable<Variable> GetVariables(this IVariableContainer activity)
     {
-        var properties = activity.GetType().GetProperties();
-        var variableProps = properties.Where(x => typeof(Variable).IsAssignableFrom(x.PropertyType)).ToList();
-        var variablesProps = properties.Where(x => typeof(IEnumerable<Variable>).IsAssignableFrom(x.PropertyType)).ToList();
-        var variables = variableProps.Select(x => (Variable?)x.GetValue(activity)).Where(x => x != null).Select(x => x!).ToList();
-        var manyVariables = variablesProps.Select(x => (IEnumerable<Variable>?)x.GetValue(activity)).Where(x => x != null).SelectMany(x => x!).ToList();
+        //var properties = activity.GetType().GetProperties();
+        //var variableProps = properties.Where(x => typeof(Variable).IsAssignableFrom(x.PropertyType)).ToList();
+        //var variablesProps = properties.Where(x => typeof(IEnumerable<Variable>).IsAssignableFrom(x.PropertyType)).ToList();
+        //var variables = variableProps.Select(x => (Variable?)x.GetValue(activity)).Where(x => x != null).Select(x => x!).ToList();
+        //var manyVariables = variablesProps.Select(x => (IEnumerable<Variable>?)x.GetValue(activity)).Where(x => x != null).SelectMany(x => x!).ToList();
 
-        return variables.Concat(manyVariables).ToList();
+        //return variables.Concat(manyVariables).ToList();
+        return activity.Variables;
     }
 
     public static TDelegate GetDelegate<TDelegate>(this IActivity activity, string methodName) where TDelegate : Delegate

src/modules/Elsa.Workflows.Core/Extensions/VariableExtensions.cs

@@ -15,10 +15,20 @@ public static class VariableExtensions
     /// </summary>
     public static Variable WithWorkflowStorage(this Variable variable) => variable.WithStorage<WorkflowStorageDriver>();
     
+    /// <summary>
+    /// Configures the variable to use the <see cref="WorkflowStorageDriver"/>.
+    /// </summary>
+    public static Variable<T> WithWorkflowStorage<T>(this Variable<T> variable) => (Variable<T>)variable.WithStorage<WorkflowStorageDriver>();
+    
     /// <summary>
     /// Configures the variable to use the <see cref="MemoryStorageDriver"/>.
     /// </summary>
     public static Variable WithMemoryStorage(this Variable variable) => variable.WithStorage<MemoryStorageDriver>();
+    
+    /// <summary>
+    /// Configures the variable to use the <see cref="MemoryStorageDriver"/>.
+    /// </summary>
+    public static Variable<T> WithMemoryStorage<T>(this Variable<T> variable) => (Variable<T>)variable.WithStorage<MemoryStorageDriver>();
 
     /// <summary>
     /// Configures the variable to use the specified <see cref="IStorageDriver"/> type.

src/modules/Elsa.Workflows.Core/Extensions/WorkflowExecutionContextExtensions.cs

@@ -76,10 +76,10 @@ public static class WorkflowExecutionContextExtensions
         IActivity activity,
         ActivityExecutionContext owner,
         ActivityCompletionCallback? completionCallback = default,
-        IEnumerable<MemoryBlockReference>? references = default, object? tag = default)
+        object? tag = default)
     {
         var activityInvoker = workflowExecutionContext.GetRequiredService<IActivityInvoker>();
-        var workItem = new ActivityWorkItem(activity.Id, async () => await activityInvoker.InvokeAsync(workflowExecutionContext, activity, owner, references), tag);
+        var workItem = new ActivityWorkItem(activity.Id, async () => await activityInvoker.InvokeAsync(workflowExecutionContext, activity, owner), tag);
         workflowExecutionContext.Scheduler.Schedule(workItem);
         workflowExecutionContext.AddCompletionCallback(owner, activity, completionCallback);
     }

src/modules/Elsa.Workflows.Core/Implementations/ActivityInvoker.cs

@@ -21,20 +21,11 @@ public class ActivityInvoker : IActivityInvoker
     public async Task InvokeAsync(
         WorkflowExecutionContext workflowExecutionContext,
         IActivity activity,
-        ActivityExecutionContext? owner,
-        IEnumerable<MemoryBlockReference>? memoryReferences = default)
+        ActivityExecutionContext? owner)
     {
         // Setup an activity execution context.
         var activityExecutionContext = workflowExecutionContext.CreateActivityExecutionContext(activity, owner);
 
-        // Declare memory.
-        if (memoryReferences != null)
-        {
-            var workflowMemory = workflowExecutionContext.MemoryRegister;
-            var activityMemory = new MemoryRegister(workflowMemory);
-            activityMemory.Declare(memoryReferences);
-        }
-
         // Add the activity context to the workflow context.
         workflowExecutionContext.AddActivityExecutionContext(activityExecutionContext);
 

src/modules/Elsa.Workflows.Core/Implementations/DefaultWorkflowExecutionContextFactory.cs

@@ -41,9 +41,6 @@ public class DefaultWorkflowExecutionContextFactory : IWorkflowExecutionContextF
         // Build graph.
         var graph = await _activityWalker.WalkAsync(root, cancellationToken);
 
-        // Assign identities.
-        _identityGraphService.AssignIdentities(graph);
-
         // Create scheduler.
         var scheduler = _schedulerFactory.CreateScheduler();
 

src/modules/Elsa.Workflows.Core/Implementations/IdentityGraphService.cs

@@ -12,7 +12,7 @@ public class IdentityGraphService : IIdentityGraphService
         _activityWalker = activityWalker;
     }
 
-    public async Task AssignIdentitiesAsync(Workflow workflow, CancellationToken cancellationToken = default) => await AssignIdentitiesAsync(workflow.Root, cancellationToken);
+    public async Task AssignIdentitiesAsync(Workflow workflow, CancellationToken cancellationToken = default) => await AssignIdentitiesAsync((IActivity)workflow, cancellationToken);
 
     public async Task AssignIdentitiesAsync(IActivity root, CancellationToken cancellationToken = default)
     {
@@ -29,7 +29,9 @@ public class IdentityGraphService : IIdentityGraphService
         {
             node.Activity.Id = CreateId(node, identityCounters, list);
             AssignInputOutputs(node.Activity);
-            AssignVariables(node.Activity);
+            
+            if(node.Activity is IVariableContainer variableContainer)
+                AssignVariables(variableContainer);
         }
     }
 
@@ -64,7 +66,7 @@ public class IdentityGraphService : IIdentityGraphService
         }
     }
 
-    public void AssignVariables(IActivity activity)
+    public void AssignVariables(IVariableContainer activity)
     {
         var variables = activity.GetVariables();
         var seed = 0;

src/modules/Elsa.Workflows.Core/Implementations/VariablePersistenceManager.cs

@@ -33,18 +33,18 @@ public class VariablePersistenceManager : IVariablePersistenceManager
     /// <inheritdoc />
     public IEnumerable<Variable> GetVariablesInScope(ActivityExecutionContext context)
     {
-        // Get variables for the current activity's immediate composite container.
-        var immediateCompositeVariables = ((Composite?)context.ActivityNode.Ancestors()
-                .FirstOrDefault(x => x.Activity is Composite)?.Activity)?.Variables
-            .Where(x => x.StorageDriverType != null) ?? Enumerable.Empty<Variable>();
+        // Get variables between the current activity and immediate composite container.
+        var ancestors = context.ActivityNode.Ancestors();
+        
+        foreach (var node in ancestors)
+        {
+            if (node.Activity is IVariableContainer variableContainer)
+                foreach (var variable in variableContainer.Variables)
+                    yield return variable;
 
-        // Get variables for the current activity itself, if it's a container.
-        var directVariables = (context.Activity is Composite composite
-            ? composite.Variables.Where(x => x.StorageDriverType != null)
-            : Enumerable.Empty<Variable>());
-
-        // Return a concatenated list of variables.
-        return immediateCompositeVariables.Concat(directVariables);
+            if (node.Activity is Composite)
+                break;
+        }
     }
 
     /// <inheritdoc />
@@ -112,12 +112,7 @@ public class VariablePersistenceManager : IVariablePersistenceManager
     /// <inheritdoc />
     public void EnsureVariables(WorkflowExecutionContext context, IEnumerable<Variable> variables)
     {
-        var register = context.MemoryRegister;
-        foreach (var variable in variables)
-        {
-            if (!register.IsDeclared(variable))
-                register.Declare(variable);
-        }
+        foreach (var variable in variables) context.MemoryRegister.Declare(variable);
     }
 
     /// <inheritdoc />

src/modules/Elsa.Workflows.Core/Models/ActivityExecutionContext.cs

@@ -84,12 +84,12 @@ public class ActivityExecutionContext
 
     public ResumedBookmarkContext? ResumedBookmarkContext => WorkflowExecutionContext.ResumedBookmarkContext;
 
-    public async ValueTask ScheduleActivityAsync(IActivity? activity, ActivityCompletionCallback? completionCallback = default, IEnumerable<MemoryBlockReference>? references = default, object? tag = default)
+    public async ValueTask ScheduleActivityAsync(IActivity? activity, ActivityCompletionCallback? completionCallback = default, object? tag = default)
     {
-        await ScheduleActivityAsync(activity, this, completionCallback, references, tag);
+        await ScheduleActivityAsync(activity, this, completionCallback, tag);
     }
 
-    public async ValueTask ScheduleActivityAsync(IActivity? activity, ActivityExecutionContext owner, ActivityCompletionCallback? completionCallback = default, IEnumerable<MemoryBlockReference>? references = default, object? tag = default)
+    public async ValueTask ScheduleActivityAsync(IActivity? activity, ActivityExecutionContext owner, ActivityCompletionCallback? completionCallback = default, object? tag = default)
     {
         if (activity == null)
         {
@@ -100,7 +100,7 @@ public class ActivityExecutionContext
             return;
         }
 
-        WorkflowExecutionContext.Schedule(activity, owner, completionCallback, references, tag);
+        WorkflowExecutionContext.Schedule(activity, owner, completionCallback, tag);
     }
 
     public async ValueTask ScheduleActivitiesAsync(params IActivity?[] activities) => await ScheduleActivities(activities);

src/modules/Elsa.Workflows.Core/Serialization/Converters/VariableConverter.cs

@@ -3,6 +3,7 @@ using System.Text.Json.Serialization;
 using Elsa.Expressions.Helpers;
 using Elsa.Workflows.Core.Models;
 using Elsa.Workflows.Core.Services;
+using Microsoft.Extensions.Logging;
 
 namespace Elsa.Workflows.Core.Serialization.Converters;
 
@@ -12,11 +13,13 @@ namespace Elsa.Workflows.Core.Serialization.Converters;
 public class VariableConverter : JsonConverter<Variable>
 {
     private readonly IWellKnownTypeRegistry _wellKnownTypeRegistry;
+    private readonly ILogger _logger;
 
     /// <inheritdoc />
-    public VariableConverter(IWellKnownTypeRegistry wellKnownTypeRegistry)
+    public VariableConverter(IWellKnownTypeRegistry wellKnownTypeRegistry, ILogger<VariableConverter> logger)
     {
         _wellKnownTypeRegistry = wellKnownTypeRegistry;
+        _logger = logger;
     }
 
     /// <inheritdoc />
@@ -39,7 +42,7 @@ public class VariableConverter : JsonConverter<Variable>
     {
         if (string.IsNullOrWhiteSpace(source.TypeName))
             return null;
-        
+
         if (!_wellKnownTypeRegistry.TryGetTypeOrDefault(source.TypeName, out var type))
             return null;
 
@@ -47,7 +50,11 @@ public class VariableConverter : JsonConverter<Variable>
         var variable = (Variable)Activator.CreateInstance(variableGenericType)!;
 
         variable.Name = source.Name;
-        variable.Value = source.Value.ConvertTo(type);
+
+        source.Value.TryConvertTo(type)
+            .OnSuccess(value => variable.Value = value)
+            .OnFailure(e => _logger.LogWarning("Failed to convert {SourceValue} to {TargetType}", source.Value, type.Name));
+
         variable.StorageDriverType = !string.IsNullOrEmpty(source.StorageDriverTypeName) ? Type.GetType(source.StorageDriverTypeName) : default;
 
         return variable;

src/modules/Elsa.Workflows.Core/Services/IActivityInvoker.cs

@@ -8,8 +8,7 @@ public interface IActivityInvoker
     Task InvokeAsync(
         WorkflowExecutionContext workflowExecutionContext,
         IActivity activity,
-        ActivityExecutionContext? owner = default,
-        IEnumerable<MemoryBlockReference>? memoryReferences = default);
+        ActivityExecutionContext? owner = default);
 
     Task InvokeAsync(ActivityExecutionContext activityExecutionContext);
 }

src/modules/Elsa.Workflows.Core/Services/IIdentityGraphService.cs

@@ -8,5 +8,5 @@ public interface IIdentityGraphService
     Task AssignIdentitiesAsync(IActivity root, CancellationToken cancellationToken = default);
     void AssignIdentities(ActivityNode root);
     void AssignInputOutputs(IActivity activity);
-    void AssignVariables(IActivity activity);
+    void AssignVariables(IVariableContainer activity);
 }

src/modules/Elsa.Workflows.Core/Services/IVariableContainer.cs

@@ -5,7 +5,10 @@ namespace Elsa.Workflows.Core.Services;
 /// <summary>
 /// Represents a container for <see cref="Variable"/>s.
 /// </summary>
-public interface IVariableContainer
+public interface IVariableContainer : IActivity
 {
+    /// <summary>
+    /// A collection of variables within the scope of the variable container.
+    /// </summary>
     ICollection<Variable> Variables { get; }
 }

src/modules/Elsa.Workflows.Management/Serialization/Converters/ActivityJsonConverter.cs

@@ -59,9 +59,6 @@ public class ActivityJsonConverter : JsonConverter<IActivity>
         var context = new ActivityConstructorContext(doc.RootElement, newOptions);
         var activity = activityDescriptor.Constructor(context);
         
-        _identityGraphService.AssignInputOutputs(activity);
-        _identityGraphService.AssignVariables(activity);
-
         return activity;
     }
 

src/modules/Elsa.Workflows.Runtime/Implementations/ClrWorkflowDefinitionProvider.cs

@@ -59,8 +59,6 @@ public class ClrWorkflowDefinitionProvider : IWorkflowDefinitionProvider
         await workflowBuilder.BuildAsync(builder, cancellationToken);
 
         var workflow = builder.BuildWorkflow();
-        await _identityGraphService.AssignIdentitiesAsync(workflow, cancellationToken);
-
         var workflowJson = JsonSerializer.Serialize(workflow.Root, _serializerOptionsProvider.CreatePersistenceOptions());
         var materializerContext = new ClrWorkflowMaterializerContext(workflowBuilder.GetType());
         var materializerContextJson = JsonSerializer.Serialize(materializerContext, _serializerOptionsProvider.CreatePersistenceOptions());
@@ -75,7 +73,6 @@ public class ClrWorkflowDefinitionProvider : IWorkflowDefinitionProvider
             Description = workflow.WorkflowMetadata.Description,
             CustomProperties = workflow.Metadata,
             Variables = workflow.Variables,
-            //ApplicationProperties = workflow.ApplicationProperties,
             IsLatest = workflow.Publication.IsLatest,
             IsPublished = workflow.Publication.IsPublished,
             CreatedAt = workflow.WorkflowMetadata.CreatedAt == default ? _systemClock.UtcNow : workflow.WorkflowMetadata.CreatedAt,

src/modules/Elsa.Workflows.Runtime/Implementations/WorkflowDefinitionService.cs

@@ -1,22 +1,30 @@
 using Elsa.Common.Models;
 using Elsa.Workflows.Management.Services;
 using Elsa.Workflows.Core.Models;
+using Elsa.Workflows.Core.Services;
 using Elsa.Workflows.Management.Entities;
 using Elsa.Workflows.Runtime.Services;
 
 namespace Elsa.Workflows.Runtime.Implementations;
 
+/// <inheritdoc />
 public class WorkflowDefinitionService : IWorkflowDefinitionService
 {
     private readonly IWorkflowDefinitionStore _workflowDefinitionStore;
+    private readonly IIdentityGraphService _identityGraphService;
     private readonly IEnumerable<IWorkflowMaterializer> _materializers;
 
-    public WorkflowDefinitionService(IWorkflowDefinitionStore workflowDefinitionStore, IEnumerable<IWorkflowMaterializer> materializers)
+    /// <summary>
+    /// Constructor.
+    /// </summary>
+    public WorkflowDefinitionService(IWorkflowDefinitionStore workflowDefinitionStore, IIdentityGraphService identityGraphService, IEnumerable<IWorkflowMaterializer> materializers)
     {
         _workflowDefinitionStore = workflowDefinitionStore;
+        _identityGraphService = identityGraphService;
         _materializers = materializers;
     }
 
+    /// <inheritdoc />
     public async Task<Workflow> MaterializeWorkflowAsync(WorkflowDefinition definition, CancellationToken cancellationToken = default)
     {
         var provider = _materializers.FirstOrDefault(x => x.Name == definition.MaterializerName);
@@ -24,9 +32,15 @@ public class WorkflowDefinitionService : IWorkflowDefinitionService
         if (provider == null)
             throw new Exception("Provider not found");
 
-        return await provider.MaterializeAsync(definition, cancellationToken);
-    }
+        var workflow = await provider.MaterializeAsync(definition, cancellationToken);
+        
+        // Assign identities.
+        await _identityGraphService.AssignIdentitiesAsync(workflow, cancellationToken);
 
+        return workflow;
+    }
+    
+    /// <inheritdoc />
     public async Task<WorkflowDefinition?> FindAsync(string definitionId, VersionOptions versionOptions, CancellationToken cancellationToken = default) =>
         await _workflowDefinitionStore.FindByDefinitionIdAsync(definitionId, versionOptions, cancellationToken);
 }

src/modules/Elsa.Workflows.Runtime/Services/IWorkflowDefinitionService.cs

@@ -9,6 +9,13 @@ namespace Elsa.Workflows.Runtime.Services;
 /// </summary>
 public interface IWorkflowDefinitionService
 {
+    /// <summary>
+    /// Constructs an executable <see cref="Workflow"/> from the specified <see cref="WorkflowDefinition"/>.
+    /// </summary>
     Task<Workflow> MaterializeWorkflowAsync(WorkflowDefinition definition, CancellationToken cancellationToken = default);
+    
+    /// <summary>
+    /// Looks for a <see cref="WorkflowDefinition"/> by the specified definition ID and <see cref="VersionOptions"/>.
+    /// </summary>
     Task<WorkflowDefinition?> FindAsync(string definitionId, VersionOptions versionOptions, CancellationToken cancellationToken = default);
 }

test/Elsa.IntegrationTests/Activities/Flowchart/Services/Workflows.cs

@@ -2,6 +2,7 @@ using System.Collections.Generic;
 using Elsa.Workflows.Core;
 using Elsa.Workflows.Core.Activities;
 using Elsa.Workflows.Core.Activities.Flowchart.Models;
+using Elsa.Workflows.Core.Implementations;
 using Elsa.Workflows.Core.Models;
 using Elsa.Workflows.Core.Services;
 
@@ -18,7 +19,7 @@ class Workflow1 : WorkflowBase
 
     protected override void Build(IWorkflowBuilder workflow)
     {
-        var currentItem = workflow.WithVariable<string>("CurrentValue", "", StorageDriverNames.Memory);
+        var currentItem = workflow.WithVariable<string>("CurrentValue", "").WithMemoryStorage();
         var writeLine1 = new WriteLine { Id = "WriteLine1", Text = new Input<string>("Start!") };
         var forEach1 = new ForEach<string> { Id = "ForEach1", Items = new Input<ICollection<string>>(_items), CurrentValue = new Output<string?>(currentItem) };
         var writeLine2 = new WriteLine { Id = "WriteLine2", Text = new Input<string>("Current Item") };
@@ -51,7 +52,7 @@ class Workflow2 : WorkflowBase
 
     protected override void Build(IWorkflowBuilder workflow)
     {
-        var currentItem = workflow.WithVariable<string>("CurrentValue", "", StorageDriverNames.Memory);
+        var currentItem = workflow.WithVariable<string>("CurrentValue", "").WithMemoryStorage();
         var writeLine1 = new WriteLine { Id = "WriteLine1", Text = new Input<string>("Start!") };
         var forEach1 = new ForEach<string> { Id = "ForEach1", Items = new Input<ICollection<string>>(_items), CurrentValue = new Output<string?>(currentItem) };
         var writeLine2 = new WriteLine { Id = "WriteLine2", Text = new Input<string>(currentItem) };
@@ -82,7 +83,7 @@ class Workflow3 : WorkflowBase
 
     protected override void Build(IWorkflowBuilder workflow)
     {
-        var currentItem = workflow.WithVariable<string>("CurrentValue", "", StorageDriverNames.Memory);
+        var currentItem = workflow.WithVariable<string>("CurrentValue", "").WithMemoryStorage();
         var writeLine1 = new WriteLine { Id = "WriteLine1", Text = new Input<string>("Start!") };
 
         var forEach1 = new ForEach<string>