JsonElement does not respect JsonSerializerOptions

[iinuwa]

Description

While trying to serialize a JsonElement with Pascal case properties to camel case, I expected that I could just set the JsonSerializerOptions.PropertyNamingPolicy to JsonNamingPolicy.CamelCase and be done. However, according to my tests and the source code, the JsonCoverter for that type just writes out the raw JSON it parsed, without transforming property names.

Reproduction Steps

using System.Text;
using System.Text.Json;

var json = @"{""ShouldWindUpAsCamelCase"":""does it?""}";
var reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(json));
var element = JsonElement.ParseValue(ref reader);
var options = new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase };
var serialized = JsonSerializer.Serialize(element, options);
Console.WriteLine(serialized);
// returns {"ShouldWindUpAsCamelCase":"does it?"} instead of {"shouldWindUpAsCamelCase":"does it?"}

Expected behavior

JsonElement serialization should respect JsonSerializerOptions, or at least, the PropertyNamingPolicy option.

Actual behavior

The serialized JsonElement just returns the case of the original JSON, ignoring all JsonSerializationOptions.

Regression?

No, I don't think this was available in previous releases.

Known Workarounds

No response

Configuration

Version: .NET 6.0, though this code was introduced in .NET 5.0.

Other information

No response

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Issue Details

---

Description

While trying to serialize a JsonElement with Pascal case properties to camel case, I expected that I could just set the JsonSerializerOptions.PropertyNamingPolicy to JsonNamingPolicy.CamelCase and be done. However, according to my tests and the source code, the JsonCoverter for that type just writes out the raw JSON it parsed, without transforming property names.

Reproduction Steps

using System.Text;
using System.Text.Json;

var json = @"{""ShouldWindUpAsCamelCase"":""does it?""}";
var reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(json));
var element = JsonElement.ParseValue(ref reader);
var options = new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase };
var serialized = JsonSerializer.Serialize(element, options);
Console.WriteLine(serialized);
// returns {"ShouldWindUpAsCamelCase":"does it?"} instead of {"shouldWindUpAsCamelCase":"does it?"}

Expected behavior

JsonElement serialization should respect JsonSerializerOptions, or at least, the PropertyNamingPolicy option.

Actual behavior

The serialized JsonElement just returns the case of the original JSON, ignoring all JsonSerializationOptions.

Regression?

No, I don't think this was available in previous releases.

Known Workarounds

No response

Configuration

Version: .NET 6.0, though this code was introduced in .NET 5.0.

Other information

No response

Author:	iinuwa
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[eiriktsarpalis]

This is by design -- the JsonDocument and JsonElement converters implement serialization using the WriteTo method. This reflects the design of JsonDocument: it's a read-only wrapper around a JSON encoded buffer focusing on performance. It does validate that the encoding is valid JSON but will otherwise copy the contents essentially verbatim.

Starting with .NET 6 my recommendation is to use JsonNode instead: it's a read-writer JSON DOM representation that offers some degree customizing serialization.