JsonPropertyName inheritance perserve the parent member

[goyzhang]

When JsonPropertyName is applied to a sub-class override member, the original name in the parent class is preserved in the output of JsonSerializer.Serialize, as a result, that's two JSON field. I don't think this is by design?

Description

abstract class Person
{
    public abstract string Name { get; set; }
}
class Student : Person
{
    [JsonPropertyName("StudentName")]
    public override string Name { get; set; }
}

var json = JsonSerializer.Serialize(new Student() { Name = "Alice" });

• Expected:
  {"StudentName":"Alice"}
• Actual:
  {"StudentName":"Alice","Name":"Alice"}

Configuration

• Which version of .NET is the code running on?
  .NET 5.0.2
• What OS and version, and what distro if applicable?
  Windows 10 2004
• What is the architecture (x64, x86, ARM, ARM64)?
  X64

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Issue Details

---

When JsonPropertyName is applied to a sub-class override member, the original name in the parent class is preserved in the output of JsonSerializer.Serialize, as a result, that's two JSON field. I don't think this is by design?

Description

	abstract class Person
	{
		public abstract string Name { get; set; }
	}
	class Student : Person
	{
		[JsonPropertyName("StudentName")]
		public override string Name { get; set; }
	}

var json = JsonSerializer.Serialize(new Student() { Name = "Alice" });

• Expected:
  {"StudentName":"Alice"}
• Actual:
  {"StudentName":"Alice","Name":"Alice"}

Configuration

• Which version of .NET is the code running on?
  .NET 5.0.2
• What OS and version, and what distro if applicable?
  Windows 10 2004
• What is the architecture (x64, x86, ARM, ARM64)?
  X64

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

[eiriktsarpalis]

That seems like a bug to me. FWIW I can reproduce the same behaviour when I create this combination:

public abstract class Person
{
    [JsonPropertyName("StudentName")]
    public virtual string Name { get; }
}
public class Student : Person
{
    public override string Name => "Bob";
}

but the issue goes away when I remove the JsonPropertyName attribute altogether. cc @layomia

[devsko]

@eiriktsarpalis I can have a look. Even if it's a bug - fixing this would be a breaking change.

[layomia]

Triage - this isn't a regression from .NET 5.0 and I think it's a bit too late in the 6.0 wave to introduce a breaking change like this. We should consider in .NET 7.0.