From f9af5e71d65901b596288a0e876bc8d2ca54044e Mon Sep 17 00:00:00 2001
From: Sipke Schoorstra <sipkeschoorstra@outlook.com>
Date: Wed, 6 Nov 2019 21:11:16 +0100
Subject: [PATCH] Improve expression evaluation (#133)

* Add test case for object-to-string target type

* Add exception handling
---
 .../Expressions/WorkflowExpressionEvaluator.cs   | 16 ++++++++++++++--
 .../Services/JavaScriptExpressionEvaluator.cs    |  4 ++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/core/Elsa.Core/Expressions/WorkflowExpressionEvaluator.cs b/src/core/Elsa.Core/Expressions/WorkflowExpressionEvaluator.cs
index 78d8af460..8fe25d8a1 100644
--- a/src/core/Elsa.Core/Expressions/WorkflowExpressionEvaluator.cs
+++ b/src/core/Elsa.Core/Expressions/WorkflowExpressionEvaluator.cs
@@ -5,16 +5,19 @@ using System.Threading;
 using System.Threading.Tasks;
 using Elsa.Services;
 using Elsa.Services.Models;
+using Microsoft.Extensions.Logging;
 
 namespace Elsa.Expressions
 {
     public class WorkflowExpressionEvaluator : IWorkflowExpressionEvaluator
     {
         private readonly IDictionary<string, IExpressionEvaluator> evaluators;
+        private readonly ILogger logger;
 
-        public WorkflowExpressionEvaluator(IEnumerable<IExpressionEvaluator> evaluators)
+        public WorkflowExpressionEvaluator(IEnumerable<IExpressionEvaluator> evaluators, ILogger<WorkflowExpressionEvaluator> logger)
         {
             this.evaluators = evaluators.ToDictionary(x => x.Syntax);
+            this.logger = logger;
         }
 
         public async Task<object> EvaluateAsync(IWorkflowExpression expression, Type type, WorkflowExecutionContext workflowExecutionContext, CancellationToken cancellationToken)
@@ -23,7 +26,16 @@ namespace Elsa.Expressions
                 return default;
             
             var evaluator = evaluators[expression.Syntax];
-            return await evaluator.EvaluateAsync(expression.Expression, type, workflowExecutionContext, cancellationToken);
+
+            try
+            {
+                return await evaluator.EvaluateAsync(expression.Expression, type, workflowExecutionContext, cancellationToken);
+            }
+            catch (Exception e)
+            {
+                logger.LogError(e, "Error while evaluating {Expression}.", expression);
+                return $"Error while evaluating {expression.Syntax} expression \"{expression.Expression}\". Message: {e.Message}";
+            }
         }
     }
 }
\ No newline at end of file
diff --git a/src/scripting/Elsa.Scripting.JavaScript/Services/JavaScriptExpressionEvaluator.cs b/src/scripting/Elsa.Scripting.JavaScript/Services/JavaScriptExpressionEvaluator.cs
index 8eec73e5c..055815f13 100644
--- a/src/scripting/Elsa.Scripting.JavaScript/Services/JavaScriptExpressionEvaluator.cs
+++ b/src/scripting/Elsa.Scripting.JavaScript/Services/JavaScriptExpressionEvaluator.cs
@@ -110,6 +110,10 @@ namespace Elsa.Scripting.JavaScript.Services
             {
                 var obj = value.AsObject().ToObject();
                 var type = targetType ?? obj.GetType();
+
+                if (type == typeof(string))
+                    return Convert.ToString(obj);
+                
                 var json = JsonConvert.SerializeObject(obj, serializerSettings);
                 return JsonConvert.DeserializeObject(json, type, serializerSettings);
             }