Format validation error.

src/lib/Microsoft.Health.Fhir.Ingest.Template/CollectionTemplateFactory.cs

@@ -68,7 +68,7 @@ private bool IsValid(TemplateContainer rootContainer, ICollection<TemplateError>
         {
             if (!rootContainer.MatchTemplateName(TargetTemplateTypeName))
             {
-                errors.Add(new TemplateError($"Expected {nameof(rootContainer.TemplateType)} value {TargetTemplateTypeName}, actual {rootContainer.TemplateType}."));
+                errors.Add(new TemplateError($"Expected {nameof(rootContainer.TemplateType)} value {TargetTemplateTypeName}, actual {rootContainer.TemplateType ?? "Not Found"}."));
                 return false;
             }
 

src/lib/Microsoft.Health.Fhir.Ingest.Template/IValidatableObjectExtensions.cs

@@ -25,12 +25,8 @@ public static bool IsValid(this IValidatableObject input, out string error)
                 return true;
             }
 
-            builder.Append("Validation errors: ");
-            foreach (var validationError in validationErrors)
-            {
-                builder.AppendLine($"{validationError.ErrorMessage}");
-            }
-
+            builder.AppendLine("Validation errors:");
+            builder.Append(string.Join("\n", validationErrors.Select(e => e.ErrorMessage)));
             error = builder.ToString();
             return false;
         }

src/lib/Microsoft.Health.Fhir.Ingest.Template/TemplateExtensions.cs

@@ -34,11 +34,19 @@ public static T ToValidTemplate<T>(this JToken token)
 
             if (errors.Any())
             {
-                string errorMessage = string.Join(", \n", errors.Select(e => e.Message));
-                throw new InvalidTemplateException($"Failed to deserialize the template content: {errorMessage}");
+                string errorMessage = string.Join(string.Empty, errors.Select(e => FormatErrorMessage(e.Message)));
+                throw new InvalidTemplateException($"Failed to deserialize the {typeof(T).Name} content: {errorMessage}");
             }
 
             return obj;
         }
+
+        private static string FormatErrorMessage(string errMessage)
+        {
+            // Remove the path information if it was empty.
+            errMessage = errMessage.Replace("Path ''.", string.Empty);
+            errMessage = "\n  " + errMessage;
+            return errMessage;
+        }
     }
 }