Removing mapper in case of an exception while building the mapper

Author: JKamsker

LiteDB/Client/Mapper/BsonMapper.GetEntityMapper.cs

@@ -28,7 +28,24 @@ internal EntityMapper GetEntityMapper(Type type)
         mapper = new EntityMapper(type, cts.Token);
         if (_entities.TryAdd(type, mapper))
         {
-            this.BuildEntityMapper(mapper);
+            try
+            {
+                this.BuildEntityMapper(mapper);
+            }
+            catch (Exception e)
+            {
+                if (_entities.TryRemove(type, out var existingMapper))
+                {
+                    var isSameMapper = ReferenceEquals(mapper, existingMapper);
+                    if (!isSameMapper)
+                    {
+                        // Should never happen, but if it does, we need to put the existing mapper back in the cache
+                        _entities.TryAdd(type, existingMapper);
+                    }
+                }
+
+                throw new LiteException(LiteException.MAPPING_ERROR, $"Error in '{type.Name}' mapping: {e.Message}", e);
+            }
         }
         else
         {

LiteDB/Utils/LiteException.cs

@@ -59,6 +59,8 @@ public class LiteException : Exception
         public const int ILLEGAL_DESERIALIZATION_TYPE = 218;
         public const int ENTITY_INITIALIZATION_FAILED = 219;
         public const int MAPPER_NOT_FOUND = 220;
+        public const int MAPPING_ERROR = 221;
+        
 
         public const int INVALID_DATAFILE_STATE = 999;