An API version is required, but was not specified. webapi

问题

var constraintResolver = new DefaultInlineConstraintResolver()
{
    ConstraintMap =
    {
        ["apiVersion"] = typeof( ApiVersionRouteConstraint )
    }
};

config.MapHttpAttributeRoutes(constraintResolver);
config.AddApiVersioning(o => o.AssumeDefaultVersionWhenUnspecified = true);


[ApiVersion("2.05")]
[RoutePrefix("api/v{version:apiVersion}/ger")]
public class caGerController
[Route("~/api/ger/getDetail")]
[Route("getDetail")]
 GetGerData


[ApiVersion("1")]
[RoutePrefix("api/v{version:apiVersion}/gerDetail")]

public class caGerDetailsController
caGerController
[Route("~/api/gerDetail/getDetail")]
[Route("getDetail")]
 GetGerData

>>  GetGerData

result: 1) both URL working with v1 version ROUTE. 2) second URL working for both, v1 and direct without v1 route as well i.e. [Route("~/api/gerDetail/getDetail")]

3) PROBLEM: first URL is only working with v1 and its not working with direct route like " [Route("~/api/ger/getDetail")]" and getting an error as below:

"Error": {
        "Code": "ApiVersionUnspecified",
        "Message": "An API version is required, but was not specified."
}

How to solve this issue. When I change from 2.05 to 1.0 then it works but 2.0 or 2.05 both not work. Is there something separate folder require ?

回答1:

The ApiVersionUnspecified happens because all routes require an explicit API version by default. You opt out of this behavior using:

options.AssumeDefaultVersionWhenUnspecified = true

This setting means that a default API version is assumed when a client doesn't provide one. The default value is:

options.DefaultApiVersion // equals 1.0 by default

When you use the URL segment versioning method, you can't have two different controllers that both an unversioned route. The route without an API version can only map to a single controller. Since the default is "1.0" and you have a controller with the unversioned route, that's the one that will always been matched.

来源：https://stackoverflow.com/questions/49415655/an-api-version-is-required-but-was-not-specified-webapi