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POWhy does ModelState.IsValid fail for my ApiController method that has nullable parameters?
 

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  1. POWhy does ModelState.IsValid fail for my ApiController method that has nullable parameters?
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    <p>I have an ApiController method that accepts several parameters, like so:</p> <pre><code> // POST api/files public HttpResponseMessage UploadFile ( FileDto fileDto, int? existingFileId, bool linkFromExistingFile, Guid? previousTrackingId ) { if (!ModelState.IsValid) return Request.CreateResponse(HttpStatusCode.BadRequest); ... } </code></pre> <p>When I POST to this I'm putting the <code>FileDto</code> object in the body of the request, and the other parameters on the query string.</p> <p>I've already discovered that I cannot simply omit the nullable parameters - I need to put them on the query string with an empty value. So, my query looks like this when I don't want to specify a value for the nullable parameters:</p> <pre><code>http://myserver/api/files?existingFileId=&amp;linkFromExistingFile=true&amp;previousTrackingId= </code></pre> <p>This does match my controller method, and when the method is executed, the nullable parameters are indeed <code>null</code> (as you'd expect).</p> <p><strong>However</strong>, the call to <code>ModelState.IsValid</code> returns <code>false</code>, and when I examine the erorrs it's complaining about both the nullable parameters. (The other bits of the model have no errors). The message is:</p> <blockquote> <p>A value is required but was not present in the request.</p> </blockquote> <p>Why does it think that a value was required / not present? Surely (a) a value is <em>not</em> required for a nullable, and (b) a value was (sort of) present - in a null-ish sort of a way?</p>
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    1. USGary McGill
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