C# Web Api: Need to have different handlers for POST method based on input supplied

Question

I have the below implementation of a REST apis:

using System.Web.Http;  
public class DeploymentsController : ApiController
{
    public HttpResponseMessage Post(
        string subscriptionId,
        string serviceName,
        string deploymentSlot,
        CreateDeploymentInput input)
    {
    . . . 
    }

    public HttpResponseMessage Post(
        string subscriptionId,
        string serviceName,
        string deploymentSlot,
        UpdateDeploymentStatusInput input)
    {
    . . . 
    }                
 }

This is the routing:

        config.Routes.MapHttpRoute(
            name: "DeploymentSlots",
            routeTemplate: "{subscriptionId}/services/hostedservices/{serviceName}/deploymentslots/{deploymentSlot}",
            defaults: new
            {
                controller = "deployments",
            });

        config.Routes.MapHttpRoute(
            name: "Deployments",
            routeTemplate: "{subscriptionId}/services/hostedservices/{serviceName}/deployments/{deploymentName}",
            defaults: new
            {
                controller = "deployments"
            });

I wanted to add handling for a new "upgrade" action which will be like below:

POST /1d42d489-7a4f-4561-91a3-c2033c31f8c6/services/hostedservices/Mytalk123490193975/deployments/Mytalk12349019/?comp=upgrade HTTP/1.1
Content-Type: application/xml; charset=utf-8
x-ms-version: 2012-08-01
Host: localhost:33344
Content-Length: 340
Expect: 100-continue
Accept-Encoding: gzip, deflate

HTTP/1.1 100 Continue

<UpgradeDeployment xmlns="http://schemas.microsoft.com/windowsazure" xmlns:i="ht    tp://www.w3.org/2001/XMLSchema-instance"><Mode>auto</Mode><PackageUrl>http://

talkserviceshared.blob.core.windows.net/mycontainer/PackageTXlCaXp0YWxrMTIzNDkwMTkzOTc1

So I added a handler in the ApiController:

    public HttpResponseMessage Post(
        string subscriptionId,
        string serviceName,
        string deploymentSlot,
        UpgradeDeploymentInput input)
    {
    . . . 
    }      

but when I invoke it using the client, it complained "Multiple actions were found that match the request "
public HttpResponseMessage Post( string subscriptionId, string serviceName, string deploymentSlot, UpdateDeploymentStatusInput input) and
public HttpResponseMessage Post( string subscriptionId, string serviceName, string deploymentSlot, UpdateDeploymentStatusInput input)

Then I tried combining the methods into one:

public HttpResponseMessage Post(
        string subscriptionId,
        string serviceName,
        string deploymentSlot,
        object input)
{
}

and wrote code that checks the runtime type and takes different actions. But this time the invocation fails with System.InvalidOperationException

Please help before I shoot myself. I don't have time to learn this stuff from scratch, I'm time crunched.

Answer 1

I followed you up to this point:

"So I added a handler in the ApiController:"

If you actually did add a third POST method with the parameter *Upgrade*DeploymentInput input, why did the compiler complain on having two POST methods with the parameter *Update*DeploymentStatusInput input.

Could it be that you simply copied-paste the method forgetting to change input from "Update" to "Upgrade?"

Dror

Answer 2

From your post I read that you assumed that route #2 in the config will cover both POST methods #2 and #3.

I might be wrong but I suspect the problem is that if the url is the same and the argument that differs comes from the request body, WebApi doesn't have any way to differentiate between the methods - the argument's type won't be checked when selecting the route and so to WebApi both methods look the same. That's where the ambiguity comes from.

I cannot advise on the workaround as you don't specify what sort of InvalidOperation is meant - could it be that you missed a cast somewhere or tried casting without having checked the object type ?

I think that one way to solve it would be using actions:

config.Routes.MapHttpRoute(
            name: "Deployments",
            routeTemplate: "{subscriptionId}/services/hostedservices/{serviceName}/deployments/{action}/{deploymentName}",
            defaults: new
            {
                controller = "deployments"
            });

Then you'd need to decorate the methods with an attribute, e.g. [ActionName("upgrade")] and access them on different urls