Added comparer to remove duplicate CosumerExecutors. (#654)

Co-authored-by: Patrick Heemskerk <pheemskerk@inforit.nl>

src/DotNetCore.CAP/Internal/ConsumerExecutorDescriptor.cs

@@ -28,8 +28,8 @@ namespace DotNetCore.CAP.Internal
         /// <summary>
         /// Topic name based on both <see cref="Attribute"/> and <see cref="ClassAttribute"/>.
         /// </summary>
-        public string TopicName
-        {
+        public string TopicName
+        {
             get
             {
                 if (_topicName == null) 
@@ -44,11 +44,48 @@ namespace DotNetCore.CAP.Internal
                         _topicName = Attribute.Name;
                     }
                 }
-                return _topicName;
+                return _topicName;
             }
         }
     }
 
+    public class ConsumerExecutorDescriptorComparer : IEqualityComparer<ConsumerExecutorDescriptor>
+    {
+        public bool Equals(ConsumerExecutorDescriptor x, ConsumerExecutorDescriptor y)
+        {
+            //Check whether the compared objects reference the same data.
+            if (ReferenceEquals(x, y))
+            {
+                return true;
+            }
+
+            //Check whether any of the compared objects is null.
+            if (x is null || y is null)
+            {
+                return false;
+            }
+
+            //Check whether the ConsumerExecutorDescriptor' properties are equal.
+            return x.TopicName.Equals(y.TopicName, StringComparison.OrdinalIgnoreCase) &&
+                x.Attribute.Group.Equals(y.Attribute.Group, StringComparison.OrdinalIgnoreCase);
+        }
+
+        public int GetHashCode(ConsumerExecutorDescriptor obj)
+        {
+            //Check whether the object is null
+            if (obj is null) return 0;
+
+            //Get hash code for the Attribute Group field if it is not null.
+            int hashAttributeGroup = obj.Attribute?.Group == null ? 0 : obj.Attribute.Group.GetHashCode();
+
+            //Get hash code for the TopicName field.
+            int hashTopicName = obj.TopicName.GetHashCode();
+
+            //Calculate the hash code.
+            return hashAttributeGroup ^ hashTopicName;
+        }
+    }
+
     public class ParameterDescriptor
     {
         public string Name { get; set; }

src/DotNetCore.CAP/Internal/IConsumerServiceSelector.Default.cs

@@ -47,6 +47,8 @@ namespace DotNetCore.CAP.Internal
 
             executorDescriptorList.AddRange(FindConsumersFromControllerTypes());
 
+            executorDescriptorList = executorDescriptorList.Distinct(new ConsumerExecutorDescriptorComparer()).ToList();
+
             return executorDescriptorList;
         }