Amplify.js & ASP.NET Web API: Getting the error message

I’m still learning my way around ASP.NET Web API and have started using Amplify.js in my web apps to consume my web services. I originally learned about Amplify.js from John Papa’s excellent Pluralsight course, “Single Page Apps with HTML5, Web API, Knockout and jQuery”.

Today I noticed that when a server-side error occurs, I was not getting the JSON response that contains the error information in my client-side Amplify error() function (see “Exception Handling in ASP.NET Web API” for an explanation). Taking a look at the Amplify source code revealed that, “out of the box”, Amplify always sends null to the error callback function’s data parameter.

To override this behavior, I created a custom decoder that would use the XHR responseText to feed the error callback data parameter, like so:

amplify.request.decoders.mydecoder =
        function (data, status, xhr, success, error) {
            if (status === "success") {
                success(data, status);
            } else if (status === "fail" || status === "error") {
                try {
                    error(JSON.parse(xhr.responseText), status);
                } catch(er) {
                    error(xhr.responseText, status);

Now I’m able to read the Message property and any other information returned from Web API when a server-side exception is thrown.

Entity Framework DbContext and mapping decimal properties with more than 2 digits of scale

Posting this mostly as a reminder to myself that when more than two decimal places of scale (i.e. to the right of the decimal point) is needed when mapping an EF entity property, you must specify the property’s precision in your DbContext’s OnModelCreating event like so:

public class MyDbContext : DbContext, IDbContext
   protected override void OnModelCreating(DbModelBuilder modelBuilder)
      modelBuilder.Entity<OutYearPoolRate>().Property(r => r.Rate).HasPrecision(14, 8);

Failure to do so causes EF to truncate the values to 2 decimal places when updating the database.