Add a NoMemberFoundBehavior parameter to the converter. (#2)

Author: dmytro-khmara

src/StrEnum.System.Text.Json/Converters/NoMemberFoundBehavior.cs

@@ -0,0 +1,7 @@
+namespace StrEnum.System.Text.Json.Converters;
+
+public enum NoMemberFoundBehavior
+{
+    ThrowException,
+    ReturnNull
+}

src/StrEnum.System.Text.Json/Converters/StringEnumJsonConverter.cs

@@ -9,6 +9,12 @@ namespace StrEnum.System.Text.Json.Converters;
 /// <typeparam name="TStringEnum"></typeparam>
 public class StringEnumJsonConverter<TStringEnum>: JsonConverter<TStringEnum> where TStringEnum: StringEnum<TStringEnum>, new()
 {
+    private readonly NoMemberFoundBehavior _noMemberFoundBehavior;
+
+    public StringEnumJsonConverter(NoMemberFoundBehavior noMemberFoundBehavior)
+    {
+        _noMemberFoundBehavior = noMemberFoundBehavior;
+    }
     public override TStringEnum Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
     {
         var jsonValue = reader.GetString();
@@ -17,6 +23,9 @@ public override TStringEnum Read(ref Utf8JsonReader reader, Type typeToConvert,
 
         if (parsed == null || !((string)parsed).Equals(jsonValue, StringComparison.InvariantCulture))
         {
+            if (_noMemberFoundBehavior == NoMemberFoundBehavior.ReturnNull)
+                return null!;
+
             throw new JsonException($"Requested name or value '{jsonValue}' was not found in the string enum '{typeof(TStringEnum).Name}'.");
         }
 

src/StrEnum.System.Text.Json/Converters/StringEnumJsonConverterFactory.cs

@@ -6,6 +6,13 @@ namespace StrEnum.System.Text.Json.Converters;
 
 internal class StringEnumJsonConverterFactory : JsonConverterFactory
 {
+    private readonly NoMemberFoundBehavior _noMemberFoundBehavior;
+
+    public StringEnumJsonConverterFactory(NoMemberFoundBehavior noMemberFoundBehavior)
+    {
+        _noMemberFoundBehavior = noMemberFoundBehavior;
+    }
+
     private readonly ConcurrentDictionary<Type, JsonConverter> _converters = new();
 
     public override bool CanConvert(Type typeToConvert)
@@ -27,7 +34,7 @@ private JsonConverter BuildConverter(Type stringEnum)
     {
         var converterType = typeof(StringEnumJsonConverter<>).MakeGenericType(stringEnum);
 
-        var converter = Activator.CreateInstance(converterType) as JsonConverter;
+        var converter = Activator.CreateInstance(converterType,  _noMemberFoundBehavior) as JsonConverter;
 
         return converter!;
     }

src/StrEnum.System.Text.Json/JsonSerializerOptionsExtensions.cs

@@ -9,10 +9,11 @@ public static class JsonSerializerOptionsExtensions
         /// Configure System.Text.Json to serialize and deserialize string enums.
         /// </summary>
         /// <param name="options"></param>
+        /// <param name="noMemberFoundBehavior">Specifies whether to thrown an exception or use a null value for members that cannot be parsed.</param>
         /// <returns></returns>
-        public static JsonSerializerOptions UseStringEnums(this JsonSerializerOptions options)
+        public static JsonSerializerOptions UseStringEnums(this JsonSerializerOptions options, NoMemberFoundBehavior noMemberFoundBehavior = NoMemberFoundBehavior.ThrowException)
         {
-            options.Converters.Add(new StringEnumJsonConverterFactory());
+            options.Converters.Add(new StringEnumJsonConverterFactory(noMemberFoundBehavior));
 
             return options;
         }

test/StrEnum.System.Text.Json.IntegrationTests/DeserializeTests.cs

@@ -1,5 +1,6 @@
 using System.Text.Json;
 using FluentAssertions;
+using StrEnum.System.Text.Json.Converters;
 using Xunit;
 
 namespace StrEnum.System.Text.Json.IntegrationTests
@@ -30,7 +31,7 @@ public void Deserialize_GivenJsonWithEnumsValue_ShouldDeserializesItWithValidEnu
         }
 
         [Fact]
-        public void Deserialize_GivenJsonWithEnumsName_ShouldThrowAnException()
+        public void Deserialize_GivenJsonWithEnumsName_AndDefaultNoMemberBehavior_ShouldThrowAnException()
         {
             var json = @"{""sport"":""TrailRunning""}";
 
@@ -57,7 +58,7 @@ public void Deserialize_GivenJsonWithNull_ShouldDeserializesItWithNull()
         }
 
         [Fact]
-        public void Deserialize_GivenJsonWithInvalidValue_ShouldThrowAnException()
+        public void Deserialize_GivenJsonWithInvalidValue_AndDefaultNoMemberBehavior_ShouldThrowAnException()
         {
             var json = @"{""sport"":""Quidditch""}";
 
@@ -69,5 +70,18 @@ public void Deserialize_GivenJsonWithInvalidValue_ShouldThrowAnException()
             deserialize.Should().Throw<JsonException>()
                 .WithMessage("Requested name or value 'Quidditch' was not found in the string enum 'Sport'.");
         }
+
+        [Fact]
+        public void Deserialize_GivenJsonWithInvalidValue_AndReturnNullNoMemberBehavior_ShouldThrowAnException()
+        {
+            var json = @"{""sport"":""Quidditch""}";
+
+            var options = new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase }
+                .UseStringEnums(NoMemberFoundBehavior.ReturnNull);
+
+            var obj = JsonSerializer.Deserialize<DeserializedObject>(json, options);
+
+            obj.Should().BeEquivalentTo(new { Sport = (Sport?)null });
+        }
     }
 }