Question about OpenAPI and nullable value types

[marty-shields]

Hi there I was wondering if I could get some guidance on how I would best get around a situation I can't seem to find an answer to.

I have the following property which allows we to ensure the user provides a value and that it is between the range:

[Required, Range(0, int.MaxValue)]
    public int? TotalDurationMinutes { get; init; }

The problem with this comes into play with when viewing the open api document which is generated, because the type is a nullable type the openapi document is showing that this property can be null and required which is weird to me.

I have tried different things such as:

[Required, Range(0, int.MaxValue)]
public int TotalDurationMinutes { get; init; }

which gives me the expected result for the openapi generation however because binding happens between model validation it means the Required property is useless and I have no way to determine if the user has actually provided a property.

Another question for this would be for other types should as DateTime, how would I enforce the user has provided a value if the type is not the nullable version?

Or would this be going down somehow doing something within the openapi generation which would allow me to continue to use the nullable type but ignore that when it comes to the generation of the doc?

[desjoerd]

The problem with this comes into play with when viewing the open api document which is generated, because the type is a nullable type the openapi document is showing that this property can be null and required which is weird to me.

Required in Openapi and json schema means the property is required to be in the object. Because null is allowed it is allowed to send the property with the value null. If a property is not marked as required in the schema, you are allowed to omit the value (see it like Javascript undefined.

which gives me the expected result for the openapi generation however because binding happens between model validation it means the Required property is useless and I have no way to determine if the user has actually provided a property.

Because C# does not have the undefined as an option it will assign default for omitted properties (null for reference tyoes and default for value types, 0 for int)

The Required attribute only checks for null so for value types it will not work.

System.Text.Json will adhere to the required modifier which will throw an exception when a required property has been omitted ensuring a client always need to send the property with a value (null is also an option for a nullable value).

[Range(0, int.MaxValue)]
public required int? TotalDurationMinutes { get; init; }

Handling of this exception is a bit hard, related issue #64139. The main thing is, that the property is required is handled by System.Text.Json and not by the Validation.

Another question for this would be for other types should as DateTime, how would I enforce the user has provided a value if the type is not the nullable version?

You would do this with the required modifier.

Or would this be going down somehow doing something within the openapi generation which would allow me to continue to use the nullable type but ignore that when it comes to the generation of the doc?

You can always add a SchemaTransformer to modify properties on schemas.

Hope this helps!

[marty-shields]

Thanks for the in-depth response based on your recommendation it's all making sense. I may switch over to using controllers in this instance