.NET 7 Preview 7 - Polymorphic Deserialization ignores PropertyNameCaseInsensitive setting

[SefaOray]

Description

I have the following class structure

[JsonPolymorphic(TypeDiscriminatorPropertyName = nameof(ActivityType))]
[JsonDerivedType(typeof(LearnSkillActivity), (int) CareerActivities.LearnSkill)]
public abstract class BaseProfessionalActivity
{
     public abstract CareerActivities ActivityType { get; }
}

public class LearnSkillActivity : BaseProfessionalActivity
{
    public string SkillId { get; set; }

    public override CareerActivities ActivityType => CareerActivities.LearnSkill;
}

Reproduction Steps

Deserializing following json doesn't work

{
  "activityType": 0,
  "skillId": "63189799bc0a84a02ffc4bc9"
}

while the following works

{
  "ActivityType": 0,
  "skillId": "63189799bc0a84a02ffc4bc9"
}

Mind that only difference is the capical A in ActivityType

Expected behavior

Deserializes correctly without error

Actual behavior

Throws error

System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported

Regression?

No response

Known Workarounds

No response

Configuration

dotnet --version
7.0.100-preview.7.22377.5

Other information

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
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Issue Details

---

Description

I have the following class structure

[JsonPolymorphic(TypeDiscriminatorPropertyName = nameof(ActivityType))]
[JsonDerivedType(typeof(LearnSkillActivity), (int) CareerActivities.LearnSkill)]
public abstract class BaseProfessionalActivity
{
     public abstract CareerActivities ActivityType { get; }
}

public class LearnSkillActivity : BaseProfessionalActivity
{
    public string SkillId { get; set; }

    public override CareerActivities ActivityType => CareerActivities.LearnSkill;
}

Reproduction Steps

Deserializing following json doesn't work

{
  "activityType": 0,
  "skillId": "63189799bc0a84a02ffc4bc9"
}

while the following works

{
  "ActivityType": 0,
  "skillId": "63189799bc0a84a02ffc4bc9"
}

Mind that only difference is the capical A in ActivityType

Expected behavior

Deserializes correctly without error

Actual behavior

Throws error

System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported

Regression?

No response

Known Workarounds

No response

Configuration

dotnet --version
7.0.100-preview.7.22377.5

Other information

No response

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

[eiriktsarpalis]

I tend to agree that this is an omission that should be fixed. However, it doesn't meet the bar for a .NET 7 fix. As a workaround I would suggest hardcoding the expected casing as a string literal instead of using nameof.

[eiriktsarpalis]

Moving to Future as we won't be able to work on this for 8.0

[iPilot]

Serializer should also consider case options for discriminator property on serialization too. For now, discriminator property name is written as specified in attribute or contract model configuration.

I'm also wondering, as we have generic attributes now, if it is possible to implement
JsonDerivedType<T> where T : Enum
as part of polymorphic serialization.
It is common practice to use enums for such purposes, isn't it?

[Mortana89]

This is blocking our upgrade from .net 5 using Dahomey JSON polymorphism to .net 8 STJ.
Our old frontend is using lowercase type discriminators but the new front-end/any other API integration works with camelcasing. How can we work around this? Was trying to implement a custom resolver and duplicating the derived types with lowercased discriminators, but the SDK does not allow registering the same type twice