Friday, 24 April 2015

Tonight I'll Start an Open Source Project...

I'm excited. Are you? I'm babysitting for a friend, I've my laptop, time to kill and (crucially) an idea...

The Idea

You're likely aware of the various form element directives that AngularJS offers. For instance the input directive:

HTML input element control. When used together with ngModel, it provides data-binding, input state control, and validation.

You'll notice that I emphasised the word "validation" there. That's important - that's my idea. I'm using AngularJS to build SPA's and for the server side I'm using ASP.Net MVC / Web API. Crucially, my templates are actually ASP.Net MVC Partial Views. That's key.

When I send data back from my SPA back to the server it gets unmarshalled / deserialized into a C# class (view model) of some kind. When data goes the other way it's flowing back from a JSON'd view model and being used by my Angular code.

Now historically if I was building a fairly vanilla MVC app then I'd be making use of all the TextboxFor extension methods etc to generate my input elements. For example, with a view model like this:

using System.ComponentModel.DataAnnotations;

namespace App.ViewModels
{
 public class RequiredModel
 {
  [Required]
  public string RequiredField{ get; set; }
 }
}

I'd have a view like this:

@model App.ViewModels.RequiredModel
@using (Html.BeginForm())
{
 <div class="row">
  @Html.LabelFor(x => x.TextBox, "Something must be entered:")
  @Html.TextBoxFor(x => x.TextBox, true)
 </div>
}

And that would generate HTML like this:

<form action="/Demo/Required" method="post">
 <div class="row">
  <label for="TextBox">Something must be entered:</label>
  <input data-msg-required="The TextBox field is required." 
      data-rule-required="true" 
      id="TextBox" name="TextBox" type="text" value="" />
 </div>
</form>

If you look at the HTML you'll see that the Required data annotations have been propogated into the HTML in the HTML in the form of data-rule-* and data-msg-* attributes. The code above is built using my jQuery.Validation.Unobtrusive.Native project which in turn was inspired by / based upon the Unobtrusive Client Validation in ASP.NET MVC. That's right - I've done this before - or at least something quite like it.

There's clearly a strong crossover between AngularJS's input directive parameters and unobtrusive client validation. I'm planning to take the principles (and maybe some of the code) that I used on that project and see if I can't make something useful with it here. Server side validation is jolly important but I can probably save a few compute cycles on the server by making use of client side validation as well. If I'm right then I should able to come up with a mechanism that saves me from manually duplicating my server validation on the client.

The Aim

I want to be able to use HTML Helpers to propogate validation metadata from the server view models into angular form validation directive attributes. Quite a mouthful I know. What does that actually mean? Well I've got 2 ideas. Possibly I want to be able to code something like this:

@model App.ViewModels.RequiredModel
@using (Html.BeginForm())
{
 <div class="row">
  @Html.LabelFor(x => x.TextBox, "Something must be entered:")
  @Html.NgTextBoxFor(x => x.TextBox)
 </div>
}

And have HTML like this generated:

<form action="/Demo/Required" method="post">
 <div class="row">
  <label for="TextBox">Something must be entered:</label>
  <input
      ng-required="true" 
      id="TextBox" name="TextBox" type="text" value="" />
 </div>
</form>

The reservation I have about this approach is that it rather takes you away from the HTML. Yes it works (and to your seasoned MVC-er it will feel quite natural in some ways) but it feels rather heavy handed. But I'd like what I'm building to be easy for users to plug into existing code without a ton of rework. So, the other idea I'm toying with is having HTML helpers that just return a string of attributes. So if I had an angular form that looked like this:

<div ng-controller="ExampleController">
<form>
 <div class="row">
  <label>Something must be entered: 
    <input name="RequiredField" type="text" value="" />
  </label>
 </div>
</form>

I could tweak it to push in the validation directive attributes like this:

@model App.ViewModels.RequiredModel
<div ng-controller="ExampleController">
<form>
 <div class="row">
  <label>Something must be entered: 
    <input name="RequiredField" type="text" value="" @Html.NgValidationFor(x => x.RequiredField) />
  </label>
 </div>
</form>

And end up with HTML like this:

<div ng-controller="ExampleController">
<form>
 <div class="row">
  <label>Something must be entered: 
    <input name="RequiredField" type="text" value="" ng-required="true" />
  </label>
 </div>
</form>

This is a simplified example of course - it's likely that any number of validation directive attributes might be returned from NgValidationFor. And crucially if these attributes were changed on the server view model then the validation changes would automatically end up in the client HTML with this approach.

The Approach

At least to start off with I'm going to aim at creating the second of my approaches. I may come back and implement the first at some point but I think the second is a better place to start.

I'm kind of surprised no-one else has built this already actually - but I'm not aware of anything. I've had a little duckduckgo around and found no takers. The closest I've come is the excellent BreezeJS. BreezeJS does way more than I want it to - I'm planning to restrict the scope of this project to simply turning data annotations on my ASP.Net MVC server models into ng-* directive attributes in HTML. That's it.

So, general housekeeping.... I'm going to host this project on GitHub, I'm going to have Continuous Integration with AppVeyor and I'm planning to publish this via NuGet (when and if I've created something useful).

I just need a name and I'll begin. What shall I call it? Some options:

  • Angular ASP.Net MVC Extensions
  • angular-aspnet-mvc-extensions
  • Angular MVC Element Extensions
  • Angular Validation Html Helpers
  • NgValidationFor (the name of the HTML helper I made up)

Hmmmm.... None of them is particularly lighting my fire. The first four are all a bit RonSeal - which is fine.... Ug. The last one... It's a bit more pithy. Okay - I'll go with "NgValidationFor" at least for now. If something better occurs I can always change my mind.

And we're off!