How to get POST data in WebAPI?

After spending a good bit of time today trying to wrap my brain around the (significant but powerful) paradigm shift between old ways of processing web form data and how it is done with WebAPI, I thought I'd add my 2 cents to this discussion.

What I wanted to do (which is pretty common for web form processing of a POST) is to be able to grab any of the form values I want, in any order. Say like you can do if you have your data in a System.Collections.Specialized.NameValueCollection. But turns out, in WebAPI, the data from a POST comes back at you as a stream. So you can't directly do that.

But there is a cool little class named FormDataCollection (in System.Net.Http.Formatting) and what it will let you do is iterate through your collection once.

So I wrote a simple utility method that will run through the FormDataCollection once and stick all the values into a NameValueCollection. Once this is done, you can jump all around the data to your hearts content.

So in my ApiController derived class, I have a post method like this:

    public void Post(FormDataCollection formData)
    {
        NameValueCollection valueMap = WebAPIUtils.Convert(formData);

        ... my code that uses the data in the NameValueCollection
    }

The Convert method in my static WebAPIUtils class looks like this:

    /// <summary>
    /// Copy the values contained in the given FormDataCollection into 
    /// a NameValueCollection instance.
    /// </summary>
    /// <param name="formDataCollection">The FormDataCollection instance. (required, but can be empty)</param>
    /// <returns>The NameValueCollection. Never returned null, but may be empty.</returns>
    public static NameValueCollection Convert(FormDataCollection formDataCollection)
    {
        Validate.IsNotNull("formDataCollection", formDataCollection);

        IEnumerator<KeyValuePair<string, string>> pairs = formDataCollection.GetEnumerator();

        NameValueCollection collection = new NameValueCollection();

        while (pairs.MoveNext())
        {
            KeyValuePair<string, string> pair = pairs.Current;

            collection.Add(pair.Key, pair.Value);
        }

        return collection;
     }

Hope this helps!

From answer in this question: How to get Json Post Values with asp.net webapi

1. Autoparse using parameter binding; note that the dynamic is made up of JToken, hence the .Value accessor.

   public void Post([FromBody]dynamic value) {
       var x = value.var1.Value; // JToken
   }
   

2. Read just like Request.RequestUri.ParseQueryString()[key]

   public async Task Post() {        
      dynamic obj = await Request.Content.ReadAsAsync<JObject>();
      var y = obj.var1;
   }
   

3. Same as #2, just not asynchronously (?) so you can use it in a helper method

   private T GetPostParam<T>(string key) {
       var p = Request.Content.ReadAsAsync<JObject>();
       return (T)Convert.ChangeType(p.Result[key], typeof(T)); // example conversion, could be null...
   }
   

Caveat -- expects media-type application/json in order to trigger JsonMediaTypeFormatter handling.