[API Proposal]: EnumConverter support for numeric/string in but always numeric out

[benmccallum]

Background and motivation

Right now with EnumConverterOptions it's easy enough to say "allow strings" and have "0" or "MemberName" be deserialized, but by opting in to that setting it also affects all the serialization and everything is serialized as the member name string representation.

i.e. Allow strings is checked first in serialization method and outputs string before falling back to numeric.

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

Lines 154 to 158 in 10e107d

	public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
	{
	// If strings are allowed, attempt to write it out as a string value
	if (_converterOptions.HasFlag(EnumConverterOptions.AllowStrings))
	{

In our transition from Newtonsoft.Json, we found a couple of places where our clients were passing in a string, in one case even the numeric representation as a string (straight from a radio button value) so we want to accept that still, but we always want to serialize and send out the numeric representation as we were before.

Right now I need to copy-paste-modify the standard factory and converter to achieve this, but I'd love it if this was support natively via some form of options.

API Proposal

I imagine this would take shape in some modification to System.Text.Json.Serialization.Converters.EnumConverterOptions, but exactly what I'm not sure.

API Usage

Replace the standard converter with a custom one as usual.

Alternative Designs

No response

Risks

Can't think of any. Perf would be same as current string in support.

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[benmccallum]

Tagging owners as I wasn't specific enough for the bot to pull the area out, sorry.
@eiriktsarpalis @layomia @krwq @steveharter

[eiriktsarpalis]

Have you considered using JsonStringEnumConverter? Note that the converter doesn't support reading quoted numeric values, this is already tracked #58247. At this point you'd need a custom converter to cover your use case I'm afraid.

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Issue Details

---

Background and motivation

Right now with EnumConverterOptions it's easy enough to say "allow strings" and have "0" or "MemberName" be deserialized, but by opting in to that setting it also affects all the serialization and everything is serialized as the member name string representation.

i.e. Allow strings is checked first in serialization method and outputs string before falling back to numeric.

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

Lines 154 to 158 in 10e107d

	public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
	{
	// If strings are allowed, attempt to write it out as a string value
	if (_converterOptions.HasFlag(EnumConverterOptions.AllowStrings))
	{

In our transition from Newtonsoft.Json, we found a couple of places where our clients were passing in a string, in one case even the numeric representation as a string (straight from a radio button value) so we want to accept that still, but we always want to serialize and send out the numeric representation as we were before.

Right now I need to copy-paste-modify the standard factory and converter to achieve this, but I'd love it if this was support natively via some form of options.

API Proposal

I imagine this would take shape in some modification to System.Text.Json.Serialization.Converters.EnumConverterOptions, but exactly what I'm not sure.

API Usage

Replace the standard converter with a custom one as usual.

Alternative Designs

No response

Risks

Can't think of any. Perf would be same as current string in support.

Author:	benmccallum
Assignees:	-
Labels:	api-suggestion, area-System.Text.Json, untriaged
Milestone:	-

[benmccallum]

Hi @eiriktsarpalis , I looked at JsonStringEnumConverter but I think it's just a factory which instantiates the core enum converter and passes the flags to support string:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonStringEnumConverter.cs

Lines 39 to 45 in d9afc1e

	public JsonStringEnumConverter(JsonNamingPolicy? namingPolicy = null, bool allowIntegerValues = true)
	{
	_namingPolicy = namingPolicy;
	_converterOptions = allowIntegerValues
	? EnumConverterOptions.AllowNumbers | EnumConverterOptions.AllowStrings
	: EnumConverterOptions.AllowStrings;
	}

The bug you mentioned would be a blocker for us, but I believe even if that's solved the result of JsonStringEnumConverter opting in to string conversion would still mean it'd force serialization out as the string repesentation (member name) as that flag is checked first.

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

Lines 154 to 158 in 10e107d

	public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
	{
	// If strings are allowed, attempt to write it out as a string value
	if (_converterOptions.HasFlag(EnumConverterOptions.AllowStrings))
	{

Workaround
I've solved my issue for now with a custom converter and factory based on the standard one, just working around some internals and always writing out the numeric value. Here's a gist if anyone has the same need.

I'll leave it in your court as to whether there's need for what I'm asking as an option flag. I think it'd be useful, but sure you've all got more important things to get on with :)

[eiriktsarpalis]

In that case, I'm going to close this in favor of #58247.

[benmccallum]

To be clear, #58247 isn't a fix for this. My custom converter is the only way.

[eiriktsarpalis]

IIRC the primary blocker even if #58247 were fixed is that you'd need to serialize as numbers? Yeah, there are all sorts of permutations wrt serialization vs deserialization behavior that the default converter won't be supporting. Recommend using a custom converter to solve your use case.