Web Api Parameter binding: snake_case to camelCase

Question

I'm doing some work on a new web api project, and my methods/ parameters follow the standard c# naming format; the method name is PascalCase, the parameters are camelCase.

Unfortunately I just discovered that documentation to a client has been published with all the parameters being ruby/ php style, with snake_case type parameter names.

The return objects and POST object were easy to convert; I used a version of crallen's code to replace the default Json input/ output, but on GET requests, there doesn't seem to be such an easy answer.

I'd prefer to keep my naming conventions the same. Is there a way to tell the binder to automatically change my_parameter into myParameter for all requests? Do I have to build a completely different binder?

For example, if I have this as a method signature:

[Route("~/api/Widgets")]
[ResponseType(typeof(Widget))]
public async Task<HttpResponseMessage> GetWidget(int widgetId, int groupId)
{
    . . .

I would like to be able to use this in the URL

https://myserver.com/api/Widgets?widget_id=12345&group_id=54321

Do I have to reinvent the wheel to get this to work? I've seen examples of replacing specific type model binders, but nothing at this level. Am I better off just changing my parameter names in code?

Answer 1

You can achieve this by using a custom ApiControllerActionSelector that rewrites Request.RequestUri and then calls the base selector.

Here it goes:

First, create the custom selector:

public class SnakeCaseActionSelector : ApiControllerActionSelector
{
    public override HttpActionDescriptor SelectAction(HttpControllerContext controllerContext)
    {
        var newUri = CreateNewUri(
            controllerContext.Request.RequestUri, 
            controllerContext.Request.GetQueryNameValuePairs());

        controllerContext.Request.RequestUri = newUri;

        return base.SelectAction(controllerContext);
    }

    private Uri CreateNewUri(Uri requestUri, IEnumerable<KeyValuePair<string, string>> queryPairs)
    {
        var currentQuery = requestUri.Query;
        var newQuery = ConvertQueryToCamelCase(queryPairs);
        return new Uri(requestUri.ToString().Replace(currentQuery, newQuery));
    }

    private static string ConvertQueryToCamelCase(IEnumerable<KeyValuePair<string, string>> queryPairs)
    {
        queryPairs = queryPairs
            .Select(x => new KeyValuePair<string, string>(x.Key.ToCamelCase(), x.Value));

        return "?" + queryPairs
            .Select(x => String.Format("{0}={1}", x.Key, x.Value))
            .Aggregate((x, y) => x + "&" + y);
    }
}

Next, create some extensions to convert to camel case and to convert to capitalized words:

public static class StringExtensions
{
    public static string ToCamelCase(this string source)
    {
        var parts = source
            .Split(new[] { '_' }, StringSplitOptions.RemoveEmptyEntries);

        return parts
            .First().ToLower() +
            String.Join("", parts.Skip(1).Select(ToCapital));
    }

    public static string ToCapital(this string source)
    {
        return String.Format("{0}{1}", char.ToUpper(source[0]), source.Substring(1).ToLower());
    }
}

And finally add the action selector to the WebApiConfig:

config.Services.Replace(typeof(IHttpActionSelector), new SnakeCaseActionSelector());