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Johnny Kauffman
Johnny Kauffman

Reputation: 3683

MVC3 Views : Handling null models with finesse

All too often I've run into a situation in which a view in my project throws a null reference exception. 

@model Johnny.Application.TestModel
<div>@(Model.SomeText)</div>

This throws an error if Model is null.

But how are people handling this? I certainly don't see code samples everywhere with ugly null checks littering the code in the view. That leads me to believe that most of the time, controllers aren't supposed to return null models. But how can you enforce this with more finesse?

Right now as soon as someone accidentally causes a controller to return a null model, the view model blows up and looks to be at fault. In reality, it was the controller's fault. And the view may not even "catch" the problem, it will only do so if the model's members happen to get used (which is most of the time, of course).

For various reasons, some views may want to handle null values. I wouldn't expect this to be the majority case, though. Clearly this is the matter of setting some "contract" between view and controller.

I don't like the options I've seen:

  1. Check if model is null every time it's used. Very lame!
  2. One big if statement wrapping the whole view with a null model check. Think of the wasted code real estate. Lame!
  3. Add an if check with a throw at the top. Not bad, but seems silly. Mildly lame.

I would love to know if something like these options existed to set the "no nulls" contract:

Upvotes: 6

Views: 1740

Answers (3)

Jordan
Jordan

Reputation: 2758

I check for nulls in my views sometimes in parts of it that require it.

I also will sometimes create default values in my controller if there is going to be a null value depends on what you are trying to do and what is acceptable.

I have for instance a case where people subscribe to something and set notifications. If they have no notifications a sub-object of my model is null. I don't want to set default values so I have a check there. In other sections i just use a default value.

Upvotes: 0

Adam Tuliper
Adam Tuliper

Reputation: 30152

There are many preferences here, some that you can do are:

  1. Throw RecordNotFoundException in your data layer (custom exception) and have a global exception filter catch this
  2. Check for nulls coming back from your repository and handle in a case by case scenario
  3. Decorate your controllers to look for a null model on GET methods that aren't CREATE methods (or whatever rules you deem OK) with an action filter attribute to check for this in OnActionExecuted

Even my "CREATE" views generally get a model, even if empty (although quite often have a IEnumerable<SelectListItem> in them), so they should always have model going to them.

Upvotes: 0

user74754
user74754

Reputation:

I asked a similar question here Should one try to guard against null reference exceptions / index out of bounds exceptions in MVC views? and got good responses to it. In short, it is preferred to add null checks in your controllers and perhaps even unit tests rather than in your views.

Upvotes: 2

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