Posting JSON Data to ASP.NET MVC

Take a look at Phil Haack’s post on model binding JSON data. The problem is that the default model binder doesn’t serialize JSON properly. You need some sort of ValueProvider OR you could write a custom model binder:

using System.IO;
using System.Web.Script.Serialization;

public class JsonModelBinder : DefaultModelBinder {
        public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) {
            if(!IsJSONRequest(controllerContext)) {
                return base.BindModel(controllerContext, bindingContext);
            }

            // Get the JSON data that's been posted
            var request = controllerContext.HttpContext.Request;
            //in some setups there is something that already reads the input stream if content type="application/json", so seek to the begining
            request.InputStream.Seek(0, SeekOrigin.Begin);
            var jsonStringData = new StreamReader(request.InputStream).ReadToEnd();

            // Use the built-in serializer to do the work for us
            return new JavaScriptSerializer()
                .Deserialize(jsonStringData, bindingContext.ModelMetadata.ModelType);

            // -- REQUIRES .NET4
            // If you want to use the .NET4 version of this, change the target framework and uncomment the line below
            // and comment out the above return statement
            //return new JavaScriptSerializer().Deserialize(jsonStringData, bindingContext.ModelMetadata.ModelType);
        }

        private static bool IsJSONRequest(ControllerContext controllerContext) {
            var contentType = controllerContext.HttpContext.Request.ContentType;
            return contentType.Contains("application/json");
        }
    }

public static class JavaScriptSerializerExt {
        public static object Deserialize(this JavaScriptSerializer serializer, string input, Type objType) {
            var deserializerMethod = serializer.GetType().GetMethod("Deserialize", BindingFlags.NonPublic | BindingFlags.Static);

            // internal static method to do the work for us
            //Deserialize(this, input, null, this.RecursionLimit);

            return deserializerMethod.Invoke(serializer,
                new object[] { serializer, input, objType, serializer.RecursionLimit });
        }
    }

And tell MVC to use it in your Global.asax file:

ModelBinders.Binders.DefaultBinder = new JsonModelBinder();

Also, this code makes use of the content type=”application/json” so make sure you set that in jquery like so:

$.ajax({
    dataType: "json",
    contentType: "application/json",            
    type: 'POST',
    url: '/Controller/Action',
    data: { 'items': JSON.stringify(lineItems), 'id': documentId }
});