System.Text.Json can't deserialize ISO dateTime to DateOnly

[marcinjahn]

Description

It looks like System.Text.Json cannot deserialize from ISO 8601 datetime string to DateOnly, which I find odd, since DateOnly.Parse("2024-05-01T00:00:00") works perfectly fine.

Reproduction Steps

Here's the code:

record MyRecord(DateOnly Date);

var serialized = "{ \"Date\": \"2025-05-01T00:00:00\" }";

System.Text.Json.JsonSerializer.Deserialize<MyRecord>(serialized); // throws

Expected behavior

I'd expect no exception to be thrown and an isntance of MyRecord to be created.

Actual behavior

An exception is thrown:

The JSON value could not be converted to Submission#1+MyRecord. Path: $.Date | LineNumber: 0 | BytePositionInLine: 31.

Regression?

No response

Known Workarounds

Use DateTime instead of DateOnly.

Configuration

dotnet: 8.0.204
OS: Fedora 40
arch: x64

Other information

No response

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[gregsdennis]

Possible duplicate of #85545 (maybe just related)

[eiriktsarpalis]

I believe this was a deliberate decision for the built-in to avoid loss of information (same is true for TimeOnly). I wouldn't be opposed to a PR that extends this to full ISO dates, if you're willing to put up a PR.

cc @Jozkee

[marcinjahn]

I think it's expected that the time portion of the datetime string will be lost when you're deserializing to a DateOnly. It's kind of similar to how you might have a type:

record (int PropOne, int PropB);

and then you try to deserialize:

{
  "PropOne": 1,
  "PropTwo": 2,
  "PropThree": 3
}

The PropThree field gets lots, and it's expected.

I will try to prepare a PR for it. I will see if I manage to build it locally. If not, I guess I could rely on PR tests.