The model binding implementation in ASP.NET Web Api shares some similarities to the model binding you find in ASP.NET MVC and at the same time has some striking differences. For a more detailed discussion on web api parameter binding, check out Mike Stall’s excellent post on the topic. The topic of today’s post is how we define our own convention for parameter binding complex types when the request is a HTTP GET request.

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TL;DR

I have written a ValueProvider for binding model collections from records in a CSV file. The source code is available on BitBucket.

Model binding in ASP.NET MVC is responsible for binding values to the models that form the parameter arguments to the controller action matched to the route. But where do model binders get these values from? That’s where Value Providers come in; A ValueProvider provides values for model binding and there are ValueProviders for providing values from

• a parent action (if the action is a child or nested action)
• a posted form value collection
• posted JSON
• route data
• the query string
• posted files

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The Norwegian Developers Conference is one of the largest .NET Developer conferences of the year, running over several days and including presentations on topics as wide-ranging as software architecture, SOLID principles, Test-Driven Development and more specific introductions to technologies such as ASP.NET 4.5, Web API, NodeJS and NServiceBus. Sufficed to say, there is something there for every .NET developer. Interested in seeing what SignalR is all about? Check out the following presentation from Damian Edwards:

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How many times have you come across the following kind of code in JavaScript

// code in script-1.js

// eek, two global variables!
var dialog, 
    updateMessage = function updateMessage (message) {        
      dialog.text(message);    
    }

// function to run when the DOM has loaded
$(function () {
    // #dialog is just a simple <p> element
    dialog = $('#dialog');
});

then in another script file

// code in script-2.js

// function to run when the DOM has loaded
$(function () {
    $('select').change(function () {
        // update the dialog with the new selection
        updateMessage('the new value is ' + this.value);
    });
});

All we’re doing here is updating the text of a <p> element in the DOM whenever the value of a <select> element changes. It’s a contrived and trivial example but it perfectly demonstrates the tight coupling between these two script files; if the updateMessage function is renamed, removed or modified to reorder the parameters (let’s put aside the use of arguments for a moment), this is going to break script-2 at runtime. What’s more, usually with these kinds of changes, it’s too easy to forget to search through all script and markup-related files for function usages and modify accordingly. And further still, it's polluted the global namespace with two additional variables (a big no no in JavaScript development), dialog and updateMessage, to allow script-2 access to the updateMessage function (which needs access to the dialog variable). There has to be a better way, and there is.

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The view engine in ASP.NET MVC is flexible, very flexible. With great flexibility comes great responsibility however, and managing JavaScript files and code blocks can be particularly cumbersome in conjunction with partial views and templates.

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If you missed Anders Hejlsberg talk on the Future directions for C# and Visual Basic, go check it out now, I’ll wait.

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Love them or hate them, the humble CAPTCHA is a tried and trusted approach to mitigating spam content from infiltrating your beautifully crafted application and flooding it with adverts selling all kinds of nefarious goods. Whilst their effectiveness is debatable and the frustration that they bring about in some high, they are relatively simple to use and catch the bulk of user defined content one would want to filter from their site.

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I'm a fan of the Data Annotation Validation attributes to validate user input on both the client and server side for ASP.NET MVC applications. I'm also a fan of Inversion of Control and Dependency Injection to create loosely coupled and flexible applications. There are certain situations where one would wish to inject services into a validation attribute to use during validation; a (somewhat contrived and security cautious) example of this might be providing the user with a <select> element and ask them to choose an option from it and then validate that the option that they have chosen is one that actually exists for the type of items represented in the dropdown. Sure, the RemoteAttribute would allow you to call a server side method via AJAX to perform validation but it does not provide any server side validation, making it more of a convenience solution than a complete and robust one. What would be good is if we could

1. provide services to a validation attribute that could be used in the process of validation
2. Not have to explicitly resolve services from the container à la the Service Locator (Anti-)Pattern

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