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POWhat, exactly, does a modelbinder do? How to use it effectively?
 

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  1. POWhat, exactly, does a modelbinder do? How to use it effectively?
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    <p>I was researching something and came across <a href="http://buildstarted.com/2010/09/12/custom-model-binders-in-mvc-3-with-imodelbinder/" rel="nofollow">this blog post at buildstarted.com</a> about model binders. It actually works pretty darn well for my purposes but I am not sure exactly whats going on behind the scenes. What I did was create a custom ModelBinder called <code>USerModelBinder</code>:</p> <pre><code>public class UserModelBinder : IModelBinder { public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) { ValueProviderResult value = bindingContext.ValueProvider.GetValue("id"); MyEntities db = new MyEntities(); User user = db.Users.SingleOrDefault(u =&gt; u.UserName == value.AttemptedValue); return user; } } </code></pre> <p>Then in my <code>Global.asax.cs</code> I have:</p> <p><code>ModelBinders.Binders.Add(typeof(User), new UserModelBinder());</code></p> <p>My understanding is that using the model binder allows me to NOT have to use the following lines in every controller action that involves a "User". So instead of passing in an "id" to the action, the modelbinder intercepts the id, fetches the correct "item"(User in my case) and forwards it to the action for processing.</p> <pre><code> MyEntities db = new MyEntities(); User user = db.Users.SingleOrDefault(u =&gt; u.UserName == value.AttemptedValue); </code></pre> <p>I also tried using an annotation on my User class instead of using the line in Global.asax.cs:</p> <pre><code>[ModelBinder(typeof(UserModelBinder))] public partial class User { } </code></pre> <p>I'm not looking for a 30 page white paper but I have no idea how the model binder does what it does. I just want to understand what happens from when a request is made to the time it is served. All this stuff "just working" is not acceptable to me, lol. Also, is there any difference between using the annotation versus adding it in Global.asax.cs? They seem to work the same in my testing but are there any gotchas?</p>
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    1. COThe one negative you may want to consider is that you are giving up the ability to modify your query to retrieve as much information as you require as possible. This is a big deal if you're using an ORM with lazy loading since it's worth writing a query that forces loading of things you know you'll need rather then letting the lazy loading mechanism load them in a separate query later.
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      1. POWhat, exactly, does a modelbinder do? How to use it effectively?
      1. USShane Courtrille
    2. COHave you come across [these](http://www.chrispfarrell.com/Blog/MVCRoutingandtheModelBinder) [articles](http://blogs.charteris.com/blogs/gopalk/archive/2009/02/11/how-does-asp-net-mvc-work-part-2.aspx)? They seem to go quite in-depth as to how it all works.
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      1. USstusherwin
 

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