Web API resolves parameters with mismatched types as missing

Question

I am using ASP.NET Core to host a Web API. I have the following action defined in my Orders controller:

[HttpGet("list")]
public List<Order> List([FromQuery] int index = 0, [FromQuery] int length = 100)
{
    return GetOrders(index, length);
}

The following returns a single order:

https://localhost:5000/api/v1/Orders/list?index=0&length=1

The following returns 100 orders:

https://localhost:5000/api/v1/Orders/list?index=0&length=a

It appears that for a request, any parameters that cannot be converted to the declared type will be treated as missing, thus resulting in the use of the default value as per the example above, or the value type default value, or null for reference types.

In this case it is preferable to have the request fail when executed with mismatched parameter types rather than have it proceed with default/null values.

Is there a way to modify this behaviour?

Answer 1

This link is a comprehensive description of how model binding works in web api: https://learn.microsoft.com/en-us/aspnet/web-api/overview/formats-and-model-binding/parameter-binding-in-aspnet-web-api

Based on it, I'd say you'll need a custom model binder that throws an exception when it cannot convert the value.