Support for overriding enum field name in JsonConverterEnum (dotnet#3…

…1081)

src/libraries/System.Text.Json/ref/System.Text.Json.cs

@@ -535,6 +535,12 @@ public JsonStringEnumConverter(System.Text.Json.JsonNamingPolicy? namingPolicy =
         public override bool CanConvert(System.Type typeToConvert) { throw null; }
         public override System.Text.Json.Serialization.JsonConverter CreateConverter(System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options) { throw null; }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Field, AllowMultiple=false)]
+    public sealed partial class JsonStringEnumMemberAttribute : System.Text.Json.Serialization.JsonAttribute
+    {
+        public JsonStringEnumMemberAttribute(string name) { }
+        public string Name { get { throw null; } }
+    }
     public sealed partial class ReferenceHandling
     {
         internal ReferenceHandling() { }

src/libraries/System.Text.Json/src/System.Text.Json.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
@@ -62,6 +62,7 @@
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonIgnoreAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonIncludeAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonPropertyNameAttribute.cs" />
+    <Compile Include="System\Text\Json\Serialization\Attributes\JsonStringEnumMemberAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\ClassType.cs" />
     <Compile Include="System\Text\Json\Serialization\ConverterList.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\Collection\ArrayConverter.cs" />

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonStringEnumMemberAttribute.cs

@@ -0,0 +1,28 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Text.Json.Serialization
+{
+    /// <summary>
+    /// Specifies the enum member that is present in the JSON when serializing and deserializing.
+    /// This overrides any naming policy specified by <see cref="JsonNamingPolicy"/>.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
+    public sealed class JsonStringEnumMemberAttribute : JsonAttribute
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="JsonStringEnumMemberAttribute"/> with the specified enum member name.
+        /// </summary>
+        /// <param name="name">The name of the enum member.</param>
+        public JsonStringEnumMemberAttribute(string name)
+        {
+            Name = name;
+        }
+
+        /// <summary>
+        /// The name of the enum member.
+        /// </summary>
+        public string Name { get; }
+    }
+}

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/EnumConverter.cs

@@ -1,10 +1,13 @@
-// Licensed to the .NET Foundation under one or more agreements.
+using System.Runtime.Serialization;
+using System.Linq;
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
 using System.Collections.Concurrent;
 using System.Globalization;
 using System.Runtime.CompilerServices;
+using System.Reflection;
 
 namespace System.Text.Json.Serialization.Converters
 {
@@ -19,6 +22,9 @@ internal class EnumConverter<T> : JsonConverter<T>
         private readonly EnumConverterOptions _converterOptions;
         private readonly JsonNamingPolicy _namingPolicy;
         private readonly ConcurrentDictionary<string, string>? _nameCache;
+        private readonly ConcurrentDictionary<T, string>? _enumToStringCache;
+        private readonly ConcurrentDictionary<ValueTuple<string?>, T>? _stringToEnumCache;
+
 
         public override bool CanConvert(Type type)
         {
@@ -42,13 +48,29 @@ public EnumConverter(EnumConverterOptions options, JsonNamingPolicy? namingPolic
                 namingPolicy = JsonNamingPolicy.Default;
             }
             _namingPolicy = namingPolicy;
+
+            if (_converterOptions.HasFlag(EnumConverterOptions.AllowStrings)) {
+                var enumType = typeof(T);
+                var fields = enumType.GetFields();
+                foreach (var field in fields) {
+                    var attribute = field.GetCustomAttribute<JsonStringEnumMemberAttribute>(false);
+
+                    if (attribute != null) {
+                        _enumToStringCache ??= new ConcurrentDictionary<T, string>();
+                        _stringToEnumCache ??= new ConcurrentDictionary<ValueTuple<string?>, T>();
+                        var enumValue = (T) Enum.Parse(enumType, field.Name);
+                        _enumToStringCache[enumValue] = attribute.Name;
+                        _stringToEnumCache[ValueTuple.Create(attribute.Name)] = enumValue;
+                    }
+                }
+            }
         }
 
         public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             JsonTokenType token = reader.TokenType;
 
-            if (token == JsonTokenType.String)
+            if (token == JsonTokenType.String || token == JsonTokenType.Null)
             {
                 if (!_converterOptions.HasFlag(EnumConverterOptions.AllowStrings))
                 {
@@ -58,13 +80,19 @@ public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerial
 
                 // Try parsing case sensitive first
                 string? enumString = reader.GetString();
-                if (!Enum.TryParse(enumString, out T value)
-                    && !Enum.TryParse(enumString, ignoreCase: true, out value))
+                if (_stringToEnumCache != null &&_stringToEnumCache.TryGetValue(ValueTuple.Create(enumString), out T value)) {
+                    return value;
+                }
+                else
                 {
-                    ThrowHelper.ThrowJsonException();
-                    return default;
+                    if (!Enum.TryParse(enumString, out value)
+                        && !Enum.TryParse(enumString, ignoreCase: true, out value))
+                    {
+                        ThrowHelper.ThrowJsonException();
+                        return default;
+                    }
+                    return value;
                 }
-                return value;
             }
 
             if (token != JsonTokenType.Number || !_converterOptions.HasFlag(EnumConverterOptions.AllowNumbers))
@@ -157,6 +185,16 @@ public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions
             // If strings are allowed, attempt to write it out as a string value
             if (_converterOptions.HasFlag(EnumConverterOptions.AllowStrings))
             {
+                if (_enumToStringCache != null &&_enumToStringCache.TryGetValue(value, out string? stringValue)) {
+                    if (stringValue != null) {
+                        writer.WriteStringValue(stringValue);
+                    }
+                    else {
+                        writer.WriteNullValue();
+                    }
+                    return;
+                }
+
                 string original = value.ToString();
                 if (_nameCache != null && _nameCache.TryGetValue(original, out string? transformed))
                 {

src/libraries/System.Text.Json/tests/Serialization/EnumConverterTests.cs

@@ -185,5 +185,32 @@ public void EnumWithConverterAttribute()
             obj = JsonSerializer.Deserialize<MyCustomEnum>("2");
             Assert.Equal(MyCustomEnum.Second, obj);
         }
+
+        [JsonConverter(typeof(JsonStringEnumConverter))]
+        public enum MyCustomJsonStringEnumMemberEnum
+        {
+            [System.Text.Json.Serialization.JsonStringEnumMemberAttribute("one_")]
+            One,
+            [System.Text.Json.Serialization.JsonStringEnumMemberAttribute("two_")]
+            Two,
+            [System.Text.Json.Serialization.JsonStringEnumMemberAttribute(null)]
+            Null
+        }
+        [InlineData("One", "\"one_\"", "0")]
+        [InlineData("Two", "\"two_\"", "1")]
+        [InlineData("Null", "null", "2")]
+        [Theory]
+        public void EnumWithJsonStringEnumMemberAttribute(string enumString, string serializedString, string serializedNumber)
+        {
+            MyCustomJsonStringEnumMemberEnum e = (MyCustomJsonStringEnumMemberEnum) Enum.Parse(typeof(MyCustomJsonStringEnumMemberEnum), enumString);
+            string json = JsonSerializer.Serialize(e);
+            Assert.Equal(serializedString, json);
+
+            MyCustomJsonStringEnumMemberEnum obj = JsonSerializer.Deserialize<MyCustomJsonStringEnumMemberEnum>(serializedString);
+            Assert.Equal(e, obj);
+
+            obj = JsonSerializer.Deserialize<MyCustomJsonStringEnumMemberEnum>(serializedNumber);
+            Assert.Equal(e, obj);
+        }
     }
 }