Thoughts on Software

Archive for the ‘ActionFilters’ Category

How to distinguish HTTP POST action methods at runtime: Checking HTTPContext Server Variables

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Following on from my last post, there is an alternative method for distinguishing whether we are dealing with an HTTP POST. Before, I suggested checking the ActionDecriptor to see whether there was an HttpPost attribute applied. An alternative to this is to check the ControllerContext for the REQUEST_METHOD server variable. If this is “POST”, then this is an HTTP POST.


public static bool IsHttpPost(ControllerContext context) 
    return context.RequestContext.HttpContext.Request.ServerVariables.Get("REQUEST_METHOD").ToUpper() == "POST"; 


Written by andrewlocatelliwoodcock

January 26, 2012 at 18:03

How to distinguish HTTP POST action methods at runtime

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I had a requirement recently to only apply an action filter to HTTP POST action methods on the controller. So the task was to create a conditional filter provider (which I will cover in a later post) which would only return the attribute if the action also had the HttpPostAttribute applied.

It turns out that it is actually quite simple to discover whether the HttpPostAttribute has been applied if you have access to an ActionDescriptor object, which you can get at from the FilterContext object available to filter attributes in their OnActionExecuting, OnActionExecuted, OnResultExecuting and OnResultExecuted methods as well as in the filter provider. Then it’s just a case of using the GetCustomAttributes and a bit of LINQ to find out if any of the action’s attributes are an HttpPostAttribute:


public static bool IsHttpPost(ActionDescriptor action)
    return action.GetCustomAttributes(typeof(HttpPostAttribute), true).Any();


Written by andrewlocatelliwoodcock

January 23, 2012 at 21:11

Accessing Model validation errors from the Controller

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MVC performs automatic model validation whilst it is binding the model, so as soon as we hit the Controller action method that is being called, we have access to a validated model. In fact, as discussed in my last post, we actually have access to the results of model validation in the method’s ActionFilters, including the first ActionFilter: OnActionExecuting, which fires before we even reach the action method.

MVC Exposes the results of this validation through the Controller’s ViewData.ModelState property. This is directly accessible in the Controller by calling ModelState and is most often used to check whether a model passed validation:


if (ModelState.IsValid)
    // model passed validation, so do some work here


But if ModelState.IsValid returns false, ie the model failed validation, how can we see the collection of errors?

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Written by andrewlocatelliwoodcock

December 16, 2011 at 20:17

Canceling the ActionExecutingContext in the OnActionExecuting ActionFilter

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I have been working recently with ActionFilters in ASP.Net MVC and was trying to prevent processing of a Controller action method from within the OnActionExecting action filter. As usual, MVC supports this level of customization, but it was not immediately obvious how to achieve it.

Specifically, I don’t like the boiler plate code required by the standard approach to only processing an action method if the model is valid and I wanted to replace it with a custom action filter instead.

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Written by andrewlocatelliwoodcock

December 15, 2011 at 12:24