C#•2y ago

deserialize non-nullable

Hello, I want to deserialize JSON with

System.Text.Json.JsonSerializer

System.Text.Json.JsonSerializer

. I have classes with

required

required

properties and it by default throws an exception if any required property is missing, which is nice, I guess. But why doesn't it throw exceptions when I have nullable reference types and the value is null:

#nullable enable
public class Test
{
    public required string Foo { get; init; }
}

#nullable enable
public class Test
{
    public required string Foo { get; init; }
}

```
{}
```
```
{}
```
is bad json - missing Foo; expected exception
```
{"Foo": 23}
```
```
{"Foo": 23}
```
is bad json - 23 is not a string; expected exception
```
{"Foo": null}
```
```
{"Foo": null}
```
is surprisingly perfectly fine. However, I would expect an exception, because null is not a valid string value in this context (Foo's type is not annotated with
```
?
```
```
?
```
- ```
string?
```
```
string?
```
  )

Is there any option that I can turn on to throw on null value? I didn't find one.

I think I understand that nullable

is only for static analysis, but I would still expect different behavior. The deserializer can check with reflection if the

is there, right? Am I missing something?

FusedQyou•6/12/24, 12:05 PM

The concept of nulabillity only exists at compile time

FusedQyou•6/12/24, 12:05 PM

So you can totally set it to because the rules no longer apply

FusedQyou•6/12/24, 12:06 PM

Try adding this method and validate the value is set and valid: https://learn.microsoft.com/en-us/dotnet/api/system.text.json.serialization.ijsonondeserialized.ondeserialized?view=net-8.0

IJsonOnDeserialized.OnDeserialized Method (System.Text.Json.Seriali...

The method that is called after deserialization.

FusedQyou•6/12/24, 12:08 PM

I believe this whole system only got introduced in C#8 so before that you didn't even have proper indications. That's why it's optional

possixOP•6/12/24, 1:16 PM

Ok, got it.
Just curious, what led the C# team to this decision where one c# feature (

required

required

, also new keyword) throws and the other (nullable reference type) does not?

Ppossix Ok, got it. Just curious, what led the C# team to this decision where one c# fea...

FusedQyou•6/12/24, 2:08 PM

Does it throw because of the

required

required

, though? I don't think it's that specifically

Pobiega•6/12/24, 2:11 PM

required

required

is also a compile-time thing

Pobiega•6/12/24, 2:12 PM

It's just that reflection code, like JSON serialization, can see the

required

required

marker and change what it does

FFusedQyou Does it throw because of the `required`, though? I don't think it's that specifi...

possixOP•6/12/24, 2:33 PM

yes according to the docs (https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/required-properties)

There are three ways to mark a property or field as required for JSON deserialization:

By adding the required modifier, which is new in C# 11.
By annotating it with JsonRequiredAttribute, which is new in .NET 7.
By modifying the JsonPropertyInfo.IsRequired property of the contract model, which is new in .NET 7.