How to force System.Text.Json deserializer to throw an exception when property is missing in JSON?

[InternalHigh]

The new UnmappedMemberHandling doesn't seem to handle this direction: Type has property, but JSON does not provide property.

class Dto
{
    public string Name { get; set; }
}

var json = "{}";

var dto = JsonSerializer.Deserialize<Dto>(json, new JsonSerializerOptions() // does not throw
{
    UnmappedMemberHandling = JsonUnmappedMemberHandling.Disallow
});

I need all properties to be required.

[pinkfloydx33]

Doesn't [JsonRequired] throw on missing values?

[InternalHigh]

Doesn't [JsonRequired] throw on missing values?

Yes but i don't want to add it to all properties. I want all properties to be required by default.

[eiriktsarpalis]

Assuming you need to do this you can use contract customization to mark every property as required:

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/custom-contracts

[Xyncgas]

why can't we just somehow use these api by saying select properties on object then make sure they are required when deserialized, imagine these api can be used like a database, instead of nested options inside JsonOptions it's so noisy

[krwq]

@Xyncgas to simply respond it's because producing contract is relatively expensive while cache is cheap. You cannot edit something in the cache because options wouldn't be thread safe but you can edit before it's created and therefore you do have access to resolver but not the cache. Also your resolver code is like 5 lines of code with resolver vs 3 with hypothetical APIs.

All you really need is (untested):

options.TypeInfoResolver = new DefaultJsonTypeInfoResolver()
{
  Modifiers =  {
  ti =>
    {
      foreach (var prop in ti.Properties)
      {
        prop.IsRequired = true;
      }
    }
  };
};