Update EnumSchema.cs to handle Enums with duplicate values

src/AvroConvert/AvroObjectServices/Schemas/EnumSchema.cs

@@ -83,7 +83,7 @@
                     int v = Convert.ToInt32(values.GetValue(i), CultureInfo.InvariantCulture);
                     this.avroToCSharpValueMapping.Add(Convert.ToInt64(values.GetValue(i), CultureInfo.InvariantCulture));
                     this.symbolToValue.Add(this.symbols[i], v);
-                    this.valueToSymbol.Add(v, this.symbols[i]);
+                    this.valueToSymbol.TryAdd(v, this.symbols[i]);
                 }
             }
         }
@@ -92,6 +92,9 @@
 
         internal bool TryGetSymbolValue(string symbol, out int value) =>
             this.symbolToValue.TryGetValue(symbol, out value);
+
+        internal int GetSymbolPosition(string symbol) =>
+            this.symbols.IndexOf(symbol);
 
         internal string GetSymbolByValue(int value)
         {

src/AvroConvert/AvroObjectServices/Write/Resolvers/Enum.cs

@@ -36,14 +36,14 @@ internal Encoder.WriteItem ResolveEnum(EnumSchema schema)
                 {
                     value = EnumParser.GetEnumName(enumType, value.ToString());
                 }
-
-                if (!schema.TryGetSymbolValue(value.ToString(), out var symbolValue))
+                var position = schema.GetSymbolPosition(value.ToString());
+                if (position < 0)
                 {
                     throw new AvroTypeException(
                         $"[Enum] Provided value is not of the enum [{schema.Name}] members");
                 }
 
-                e.WriteEnum(symbolValue);
+                e.WriteEnum(position);
             };
         }
     }

tests/AvroConvertTests/FullSerializationAndDeserialization/EnumTests.cs

@@ -146,5 +146,44 @@ public void Class_with_enum_with_member_value_attributes(Func<object, Type, dyna
             Assert.Equal(TestEnumWithMembers.Negative, deserialized.EnumPropWithDefault);
             Assert.Equal(TestEnumWithMembers.Negative, deserialized.EnumPropWithStringDefault);
         }
+
+        [Theory]
+        [MemberData(nameof(TestEngine.All), MemberType = typeof(TestEngine))]
+        public void Enum_with_duplicate_values(Func<object, Type, dynamic> engine)
+        {
+            var itemsToTest =
+            new [] {
+                TestDuplicateEnum.Test,
+                TestDuplicateEnum.Exam, //Compilation already sets these values to the primary duplicate value.
+                TestDuplicateEnum.Error,
+                TestDuplicateEnum.Fail,
+                TestDuplicateEnum.TestLabel,
+                TestDuplicateEnum.TestLabel2
+            };
+
+            foreach (var toSerialize in itemsToTest)
+            {
+                //Act
+                var deserialized = engine.Invoke(toSerialize, typeof(TestDuplicateEnum));
+
+                //Assert
+                Assert.Equal((int)toSerialize, (int)deserialized);
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(TestEngine.All), MemberType = typeof(TestEngine))]
+        public void Class_with_enum_with_duplicate_value(Func<object, Type, dynamic> engine)
+        {
+            //Arrange
+            ClassWithDuplicateEnums toSerialize = _fixture.Create<ClassWithDuplicateEnums>();
+
+            //Act
+            var deserialized = engine.Invoke(toSerialize, typeof(ClassWithDuplicateEnums));
+
+            //Assert
+            Assert.NotNull(deserialized);
+            Assert.Equal(toSerialize, deserialized);
+        }
     }
 }

tests/AvroConvertTests/TestClasses.cs

@@ -353,6 +353,25 @@ public class ClassWithEnum
         public TestEnum? SecondEnumProp { get; set; }
     }
 
+    public enum TestDuplicateEnum {
+        Test = 0,
+        Exam = Test,
+        Fail = 1,
+        Error = Fail,
+        TestLabel = 2,
+        TestLabel2 = 2
+    }
+
+    [Equals(DoNotAddEqualityOperators = true)]
+    public class ClassWithDuplicateEnums {
+        [DefaultValue(TestDuplicateEnum.Fail)]
+        public TestDuplicateEnum? EnumProp { get; set; }
+        [DefaultValue("Error")]
+        public TestDuplicateEnum? EnumProp2 { get; set;}
+        [DefaultValue(2)]
+        public TestDuplicateEnum? EnumProp3 { get; set; }
+    }
+
     public class ClassWithEnumDefiningMembers
     {
         public TestEnumWithMembers? EnumProp { get; set; }