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

[ghost]

Tagging subscribers to this area: @eiriktsarpalis, @layomia
See info in area-owners.md if you want to be subscribed.

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.

[simon10says]

Is there any workaround?

[rogerfar]

Another bug related to this issue.

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

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

Results in 2 properties:

{
    Name: 'Alice',
    StudentName: 'Alice'
}

[krwq]

Unfortunately we won't have time to address this in 7.0 but contract customization can be used to workaround this. Moving to 8.0 in the meantime

[kgbaum]

For those who may be looking for a work around until this can be addressed. You can make use of a dummy property:

abstract class Person
{
	public abstract string Name { get; set; }
}
class Student : Person
{
	[JsonIgnore]
	public override string Name { get => base.Name; set => base.Name = value; }
	
	public string StudentName { get => base.Name; set => base.Name = value; }
}

[pinkfloydx33]

Just ran into this as well. I was hoping to avoid contract customization as it feels a bit heavy for this; might try the workaround posted above instead. Would be nice if it worked out of the box though

[tanveerbadar]

This is causing source generation to generate invalid code when it interacts with JsonIgnoreCondition.WhenWritingDefault or JsonIgnoreCondition.WhenWritingNull.

#98634