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Nullable strings are not marked nullable in openapi json

See original GitHub issue

When I use a nullable property, they get marked as "nullable": true in the json output, which is correct.

But it seems this is not the case for strings. Is this a bug or is it me just being really thick here?

I tried adding [JsonProperty(Required = Required.AllowNull)] to the property, but that didn’t work either.

This is with version 0.7.2

This is my model

    public class Subscription
        public string TheString { get; set; }
        public string? TheNullableString { get; set; }

        public int TheInt { get; set; }
        public int? TheNullableInt { get; set; }

        public DateTimeOffset TheDateTime { get; set; }
        public DateTimeOffset? TheNullableDateTime { get; set; }

And this is the output from http://localhost:7071/api/openapi/v3.json

      "subscription": {
        "type": "object",
        "properties": {
          "theString": {
            "type": "string"
          "theNullableString": {
            "type": "string"    <--- missing nullable here!
          "theInt": {
            "type": "integer",
            "format": "int32"
          "theNullableInt": {
            "type": "integer",
            "format": "int32",
            "nullable": true
          "theDateTime": {
            "type": "string",
            "format": "date-time"
          "theNullableDateTime": {
            "type": "string",
            "format": "date-time",
            "nullable": true

Issue Analytics

  • State:closed
  • Created 2 years ago
  • Comments:12 (6 by maintainers)

github_iconTop GitHub Comments

MartinWickmancommented, Jun 22, 2021

Just to make it clear though:

If you have nullable references, c# 8 enabled in your project (as I have) then string email is not allowed to be null. You get a compilation error or warning if you try to assign it to null. So you absolutely should to put a ? on all nullable reference types.

So imo, it’s reasonable to expect string? to generate nullable: true in the swagger.json output. But as it stands now, you must remember to add the [OpenApiProperty(Nullable=true) for reference types. I don’t really know what gets generated in a default “non-nullable” project though.

So if you craft the REST client yourself, this is easy enough to handle, but problem is when you generate a client (in my case with Nswag), it will generate the C#-properties in the model classes without the proper “allow null” attributes, thus crashing when the server sends a null json value for that property. You end up with Newtonsoft.Json: Required property 'email' expects a non-null value.

Actually, it generates them like this:

[Newtonsoft.Json.JsonProperty("email", Required = Newtonsoft.Json.Required.DisallowNull)]
public string Email { get; set; }

Which is due to the property missing nullable: true in the swagger spec.

Otherwise, I agree with your logic: [JsonRequired] overrides [OpenApiProperty(Nullable)] which overrides the property. And if the property is nullable (?) it should generate nullable: true imo.

justinyoocommented, Jun 21, 2021

@MartinWickman I’ve updated the OpenApiPropertyAttribute that you can make use of for your nullable properties. It will be released in the next release. In the meantime, it would be great if you try the code on your end.

Read more comments on GitHub >

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