Nswag: Nswag, c# Required = Newtonsoft.Json.Required.DisallowNull, how to handle

[Unders0n]

Copy of https://stackoverflow.com/questions/54656603/swagger-nswagstudio-c-required-newtonsoft-json-required-disallownull-how , which got no attention, please help.

Given: api that i have limited influence to in terms of changing, built on net core 2.2. Standart netCore swagger used. Some classes of DTO have fields in it marked with [System.ComponentModel.DataAnnotations.Required] But for some reasons (which are also discussable) some methods return objects of this classes with nulls in this fields. Annotation resulted in

"required": [
"given", - this field for example
"family",
"email",
"postCode"
],
"type": "object",
...

in swagger spec which then results in

[Newtonsoft.Json.JsonProperty("given", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]

in c# generated code (i'm using nswag studio and c# client with pretty standart settings). And then when i'm trying to get list of such objects from api using generated c# client, if some of such properties have null it obviosly throws newtonsoft deserialization exception. so how we can handle that? I thought of both client side and server side solutions:

1)on server we can configure not to expose info about required to swagger spec.

2) on client we can possibly configure behavior of translating that Required block to Required = Newtonsoft.Json.Required.Default

3) forget about all that and insist so api will not return object with null vaues which properties market Required.

[RicoSuter]

Is this swagger 2.0 or openapi 3.0?

[Unders0n]

@RSuter as from swagger spec: "swagger": "2.0",

[RicoSuter]

To clarify the generation of this:

base.IsNullable:

The biggest problem is that Swagger 2.0 does not have a way to express nullability - so we need to use required for nullability which is technically wrong - in JSON Schema this just specifies whether the the value must be set or not...

[RicoSuter]

Another option is to transform the swagger spec before generating the clients, sample here:
https://github.com/Picturepark/Picturepark.SDK.Playground/blob/master/src/AutoRestTransformer/Program.cs

[VitalickS]

As alternative, you can manually override behavior for JsonSerializerSettings in partial class method (Client). Just add this to partial class
```c#
partial void UpdateJsonSerializerSettings(JsonSerializerSettings settings)
{
settings.ContractResolver = new SafeContractResolver();
}

class SafeContractResolver : DefaultContractResolver
{
protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
{
var jsonProp = base.CreateProperty(member, memberSerialization);
jsonProp.Required = Required.Default;
return jsonProp;
}
}
```

[kjkrum]

@RicoSuter Given that this is a limitation of Swagger 2.0, is there an official position on where the fault lies if a 2.0 API describes a property as required but then sends null for that property? Is it unequivocally a bug in the API, or is it a matter of there being no good general solution for NSwag and therefore up to the client to implement a workaround?

[kjkrum]

To shed some light on my own question, this SO Q&A suggests that an API sending a null value for a string property is wrong, _not_ because the property is required, but because null isn't a string. It sounds like Swagger 2.0 having no means to express nullability strictly means that nothing is nullable. Any way of representing nullability is just a hack, whether it's an API sending nulls, or NSwag's treatment of required. Is that correct?