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POWhy ASP.NET MVC default Model Binder is slow? It's taking a long time to do its work
 

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  1. POWhy ASP.NET MVC default Model Binder is slow? It's taking a long time to do its work
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    <p>In a current project the client asked for the possibility of answering a questionnaire in two ways: using a <code>Wizard</code> (one question at a time) and <code>Listing</code> (all questions at once) in a single form. Both ways are already implemented.</p> <p>The questions are loaded from the database per Manual's chapter using AJAX (this is super fast). The biggest chapter at the moment has <code>230</code> questions (each with 4 HTML input fields - input/text, select, etc). If the user selects such Chapter to answer in the <code>Listing</code> format, the <code>&lt;form&gt;</code> will contain at about <code>920</code> fields to be posted to the server.</p> <p>I'm doing an AJAX POST request passing the data with jQuery's <code>serialize</code> method:</p> <pre><code>data: $("#questions :input").serialize() </code></pre> <p>This serialization takes <code>207.143ms</code> to complete. I got this value debugging with Firebug in Firefox:</p> <pre><code>console.profile(); $("#questions :input").serialize(); console.profileEnd(); </code></pre> <p>Again this is super fast...</p> <p>The problem comes when hydrating the data received on the following action method:</p> <pre><code>public async Task&lt;ActionResult&gt; ListSaveAsync(IEnumerable&lt;AnswerViewModel&gt; questions) </code></pre> <p>As you see, the posted data is data bound to an <code>IEnumerable&lt;AnswerViewModel&gt; questions</code>. <code>AnswerViewModel</code> has only 4 fields to store each answer.</p> <p>The thing is that it takes a considerable amount of time (precisely 10 seconds) after clicking the Save button to hit a breakpoint on this action method, that is, those 10 seconds are being spent in the model binder presumably.</p> <p>An important thing to mention is that I'm using Steve Sanderson's <a href="http://blog.stevensanderson.com/2008/12/22/editing-a-variable-length-list-of-items-in-aspnet-mvc/" rel="nofollow noreferrer">@Html.BeginCollectionItem helper</a> to help when materializing the ViewModel collection properties from the HTTP POST. See how the data gets in the ViewModel (Keys):</p> <p><img src="https://i.stack.imgur.com/QjA5e.png" alt="enter image description here"></p> <p>Do you know what I can try to do to optimize this?</p> <p>I thought about 4 workarounds:</p> <ol> <li><p>Save back only the modified questions. To do this I'd need to store each answer value in a data-attribute when loading the listing and compare it with the actual value when submitting the <code>&lt;form&gt;</code> as this guy suggests <a href="https://stackoverflow.com/a/8043489/114029">here</a>.</p></li> <li><p>Create <code>AnswerViewModel</code> JavaScript objects on the client side and pass them to the action method. Would this alleviate the Model Binder?</p></li> <li><p>Roll my own model binder... but I really don't know if it would be faster than the default one that comes with ASP.NET MVC. From what I've read the default model binder does a lot of reflection to set the values/hydrate the action's model parameter and this could be the bottleneck.</p></li> <li><p>Use <code>FormCollection</code> and enumerate through the posted data getting each value by key and performing validation manually as shown <a href="http://stack247.wordpress.com/2011/03/20/iterate-through-system-web-mvc-formcollection/" rel="nofollow noreferrer">here</a>.</p></li> </ol> <p>What else do you suggest?</p> <hr> <p><strong>Update 1</strong></p> <p>I went with option 3 and implemented a custom Model Binder: <code>AnswerModelBinder : IModelBinder</code> and used it in that specific action method:</p> <pre><code>public async Task&lt;ActionResult&gt; ListSaveAsync( [ModelBinder(typeof(AnswerModelBinder))]List&lt;AnswerViewModel&gt; questions) </code></pre> <p>Now what took <code>10 seconds</code> to complete takes only <code>2 seconds</code>.</p> <ul> <li>Looks like the default model binder validation checks [ <code>ModelState</code> ] has a big impact on performance.</li> </ul> <p><strong>Update 2</strong></p> <p>I just experienced it once again: having a <code>List&lt;Guid&gt;</code> as an action parameter and passing only <code>59 strings</code> through a <code>$.getJson</code> call was taking ~3 seconds to hit a breakpoint in the 1st line of the action method. Changing the parameter type to <code>List&lt;string&gt;</code> made the whole thingy work in the blink of an eye.</p> <p>An interesting fact is that inside the action method I did this:</p> <pre><code>List&lt;Guid&gt; userIds = resources.Select(Guid.Parse).ToList(); </code></pre> <p>and it transforms the resources <code>List&lt;string&gt;</code> to a <code>List&lt;Guid&gt;</code> instantaneously.</p> <p>For sure there's something buggy with ASP.NET model binder. I just would like to know what it is... :)</p>
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    1. USLeniel Maccaferri
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    1. COSorry for the slow reply, Leniel. How many questions are you sending to the server? The model binder uses a lot of code to try to be very generic about parsing input from the request. I think in your case the best way to solve was the path you took.
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    2. CO@OdeToCode Thanks Scott for taking a look... Nice you agree with the custom Model Binder approach. In this specific case I'm sending 230 questions to the server. If I also do option #1, I think it'll be even faster... ;) Maybe 1s instead of 2s since JavaScript is pretty fast. Have to test this.
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      1. POWhy ASP.NET MVC default Model Binder is slow? It's taking a long time to do its work
      1. USLeniel Maccaferri
    3. CO@OdeToCode Just complemented the code and implemented workaround #1 I mention above => when loading the questions I put the each input/select current value in a data-attribute and when saving I compare the current value with that previous value in the data attribute. I then use jQuery's filter function to help with this. Now Saving is instantaneous. :-) jQuery code is impressively fast!
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