Polymorphic Serialization - Doesn't allow typeDiscriminator to be anything but first

[RyanGaudion]

Description

I have this endpoint:

[HttpPost]
public async Task<IActionResult> Add([FromBody] BaseClass test)
{
    //...
}

and my BaseClass is annotated as follows:

[JsonPolymorphic(TypeDiscriminatorPropertyName = "resourceType")]
[JsonDerivedType(typeof(DerivedClass1), typeDiscriminator: nameof(DerivedClass1))]
[JsonDerivedType(typeof(DerivedClass2), typeDiscriminator: nameof(DerivedClass2))]

When sending a json body where resourceType is anything but the first property, I get the following error:

{
	"type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
	"title": "One or more validation errors occurred.",
	"status": 400,
	"traceId": "...",
	"errors": {
		"$.resourceType": [
			"The metadata property is either not supported by the type or is not the first property in the deserialized JSON object. Path: $.resourceType | LineNumber: 2 | BytePositionInLine: 16."
		]
	}
}

Reproduction Steps

Sending this as a POST request throws the error:

{
	"prop1": 1,
	"resourceType": "DerivedClass1",
	"prop2": "test",
}

however this doesn't:

Sending this as a POST request throws the error:

{
"resourceType": "DerivedClass1",
"prop1": 1,
"prop2": "test",
}

Expected behavior

I understand the performance advantages to having the discriminator as the first property however is there a toggle/option that can be set to allow the JsonSerializer to look through the whole jsonObject first for the discriminator?

Actual behavior

....

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

[ghost]

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Issue Details

---

Description

I have this endpoint:

[HttpPost]
public async Task<IActionResult> Add([FromBody] BaseClass test)
{
    //...
}

and my BaseClass is annotated as follows:

[JsonPolymorphic(TypeDiscriminatorPropertyName = "resourceType")]
[JsonDerivedType(typeof(DerivedClass1), typeDiscriminator: nameof(DerivedClass1))]
[JsonDerivedType(typeof(DerivedClass2), typeDiscriminator: nameof(DerivedClass2))]

When sending a json body where resourceType is anything but the first property, I get the following error:

{
	"type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
	"title": "One or more validation errors occurred.",
	"status": 400,
	"traceId": "...",
	"errors": {
		"$.resourceType": [
			"The metadata property is either not supported by the type or is not the first property in the deserialized JSON object. Path: $.resourceType | LineNumber: 2 | BytePositionInLine: 16."
		]
	}
}

Reproduction Steps

Sending this as a POST request throws the error:

{
	"prop1": 1,
	"resourceType": "DerivedClass1",
	"prop2": "test",
}

however this doesn't:

Sending this as a POST request throws the error:

{
"resourceType": "DerivedClass1",
"prop1": 1,
"prop2": "test",
}

Expected behavior

I understand the performance advantages to having the discriminator as the first property however is there a toggle/option that can be set to allow the JsonSerializer to look through the whole jsonObject first for the discriminator?

Actual behavior

....

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

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

[RyanGaudion]

FYI - Using .Net 7 Preview 7

[Tornhoof]

See #72604

[layomia]

Duplicate of #72604.