Unexpected CamelCase formatting in System.Text.Json

[Ilchert]

Description

Unexpected formatting for dictionary keys using System.Text.Json.

Expected value some_3.
Actual value somE_3.

var o = new JsonSerializerOptions()
{
     DictionaryKeyPolicy = JsonNamingPolicy.CamelCase
};
var data = new Dictionary<string, object> { { "SOME_3", "" } };
var text = JsonSerializer.Serialize(data, o); // {"somE_3":""}

Configuration

• Which version of .NET is the code running on? NET5.0.101
• What OS and version, and what distro if applicable? Win10
• What is the architecture (x64, x86, ARM, ARM64)? x64
• Do you know whether it is specific to that configuration? No

Regression?

Previously the value had not changed.

[huoyaoyuan]

Are you using ASP.NET? This is a known change in ASP.NET Core 5.0.

[Ilchert]

@huoyaoyuan yes, aspnet. Could you provide a description of this change?

[huoyaoyuan]

dotnet/docs#21067

[Ilchert]

@huoyaoyuan, thanks for the link, but my issue about upper case of char E in SOME_3 -> somE_3 transformation, not about quoted numbers.

[huoyaoyuan]

The camel case handler does not have well-defind behavior for all capitalized. You should use an option to not convert the name at all. It there already such option?

[layomia]

Preliminary note that System.Text.Json has the same behavior as Newtonsoft.Json here - https://dotnetfiddle.net/ViFFmX.

We'll likely not do any work here (given it would be a non-trivial breaking change), unless something related spills out of the feature work for snake_case support (#782) in an effort to have a central algorithm between snake case, camel case, and any feature casing policies.

The work around here is to implement a custom JsonNamingPolicy which uses JsonNamingPolicy.CamelCase as the main logic, but handles edge-cases such as you've described above.