System.text.json serializes virtual property decorated with JsonPropertyName attribute twice.

[alexaloni]

Description

System.text.json serializes property decorated with JsonPropertyName attribute in the base class is recording 2 records in the output json , one with property name as key and a second with name specified in the attribute.

Reproduction Steps

Console.WriteLine(JsonSerializer.Serialize(new Derived()));

public class Base
{
    [JsonPropertyName("test")]
    public virtual string Id { get => "base"; set { } }
}

public class Derived : Base
{
    public override string Id { get => "derived"; set { } }
}

Expected behavior

only single entry with name specified in the JsonPropertyName should be adde to json.

Actual behavior

{"Id":"derived","test":"derived"} -> added twice with different names.

Regression?

We have seen this since the initial version.

Known Workarounds

I see two possible workarounds:

1. Try using the base type as the generic parameter when creating your container object. Unlike Json.NET, STJ is sensitive when it comes to what type is being declared statically at the serialization callsite, or
2. Replicate the JsonPropertyName property in the overrides. It's more boilerplate, but at least it's the best way to get the desired behavior while we ship a fix.

Configuration

.NET 7

Other information

No response

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Issue Details

---

Description

System.text.json serializes property decorated with JsonPropertyName attribute in the base class is recording 2 records in the output json , one with property name as key and a second with name specified in the attribute.

Reproduction Steps

Console.WriteLine(JsonSerializer.Serialize(new Derived()));

public class Base
{
[JsonPropertyName("test")]
public virtual string Id { get => "base"; set { } }
}

public class Derived : Base
{
public override string Id { get => "derived"; set { } }
}

Expected behavior

only single entry with name specified in the JsonPropertyName should be adde to json.

Actual behavior

{"Id":"derived","test":"derived"} -> added twice with different names.

Regression?

We have seen this since the initial version.

Known Workarounds

I see two possible workarounds:

1. Try using the base type as the generic parameter when creating your container object. Unlike Json.NET, STJ is sensitive when it comes to what type is being declared statically at the serialization callsite, or
2. Replicate the JsonPropertyName property in the overrides. It's more boilerplate, but at least it's the best way to get the desired behavior while we ship a fix.

Configuration

.NET 7

Other information

No response

Author:	alexaloni
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	-

[eiriktsarpalis]

I can reproduce in .NET 8. This falls under the same umbrella of issues described in #73255, namely it concerns attribute resolution of virtual properties. We should try to address all these issues in unison, although it would admit the probability of breaking changes.

In the meantime, you could try the following workarounds:

1. Serialize the value using the base type as the generic parameter: JsonSerializer.Serialize<Base>(new Derived()); or
2. Apply the same JsonPropertyName attribute to the overridden property.

[jmathiassen-visma]

I see you mention attribute resolution of virtual properties, I assume this is the same problem I'm seeing when I'm doing this:

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

public static class test
{
    [JsonPolymorphic(UnknownDerivedTypeHandling = JsonUnknownDerivedTypeHandling.FallBackToNearestAncestor, TypeDiscriminatorPropertyName = "action")]
    [JsonDerivedType(typeof(inherited), nameof(anEnum.attribute3))]
    public class root
    {
        [JsonConverter(typeof(JsonStringEnumConverter))]
        public anEnum action { get; set; }
        [JsonConverter(typeof(JsonStringEnumConverter))]
        public anEnum action2 { get; set; }
    }

    public class inherited : root
    {
        public string asdf { get; set; }
        public string asdf2 { get; set; }
    }

    public enum anEnum
    {
        attribute1,
        attribute2,
        attribute3,
        attribute4
    }

    static void Main(string[] args)
    {
        inherited input = new()
        {
            action = anEnum.attribute3,
            action2 = anEnum.attribute2,
            asdf = "asdf1",
            asdf2 = "asdf2",
        };
        Console.WriteLine(JsonSerializer.Serialize(input));
        Console.WriteLine(JsonSerializer.Serialize((root)input));
    }
}

The output I get is the following:

    {"asdf":"asdf1","asdf2":"asdf2","action":"attribute1","action2":"attribute2"}
    {"action":"attribute4","asdf":"asdf1","asdf2":"asdf2","action":"attribute1","action2":"attribute2"}

If I remove the jsonpolymorphic tag, and run the same code, I get the following:

{"asdf":"asdf1","asdf2":"asdf2","action":"attribute3","action2":"attribute2"}
{"$type":"attribute4","asdf":"asdf1","asdf2":"asdf2","action":"attribute3","action2":"attribute2"}

So, the first line is serialized directly from the actual instantiated class (i.e. instanced, in this case), the second is when it's serialized via the root baseclass, i.e. I assume we're seeing the actually derived object, and I assume the first property is a virtual property that in the polymorphed instance has its name overridden by the polymorphism typediscriminatorpropertyname attribute, while in the non-polymorphed instance the virtual property is just named $type.

When I deserialize it again, everything looks fine, it's only when I try to f.ex send it over the wire by serializing it via the base class that it actually turns into a problem.

[Xor-el]

here is another variation that the workarounds mentioned above does not work for.

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

var json = JsonSerializer.Serialize(new CustomerLimitTransactionLogRequest { AccountNumber = "1234567890" });

Console.WriteLine($"Json Data: {json}");

public abstract class BaseCustomerLimitRequest
{
    public virtual string? AccountNumber { get; set; }
}

public class CustomerLimitTransactionLogRequest : BaseCustomerLimitRequest
{
    [JsonPropertyName("accountNo")]
    public override string? AccountNumber { get; set; }
}