CODEWITHSUNDEEP
model-view-controllerdesign-patterns
Larsenal
Larsenal

Reputation: 51176

Excessive Null checking in MVC Views

This is a question about style and design rather than syntax.

I have domain models that have several (for lack of a better term) navigation properties. So in my strongly typed details view of Foo which has a property of type Bar I could do the following:

<%: Foo.Bar.Name %>

However, sometimes Bar is Null, so I end up with something like:

<%: Foo.Bar == null ? String.Empty : Foo.Bar.Name %>

In other cases, because the convenience of the navigation properties I could do even more chaining. The downside, however, is the introduction of more null checking in my View.

As an alternative, I could do all the null checking in a ViewModel so that I've passed off something "clean" to the View. I'm looking for some ideas or common sense guidelines for avoiding excessive null checking in my views.

P.S. I'm using ASP.NET MVC, but I think this question may be relevant to other MVC frameworks.

Upvotes: 3

Views: 823

Answers (6)

Unmesh Kondolikar
Unmesh Kondolikar

Reputation: 9312

First consider whether in your model an instance of Foo is valid if Bar is null. If no then you should put a guard clause in the constructor and\or the setter of the Bar property.

public class Foo{

        public BarClass _bar;

        public BarClass Bar{
            get{return _bar; }
            set{
                if(value == null)
                   throw new ArgumentNullException();
                _bar = value; } 
            } 

           public Foo(BarClass bar){
              if(bar == null) throw new ArgumentNullException();
              _bar = bar;
          } 
        }

Secondly, too many and duplicated null checks is a code smell. You should use the refactoring Replace Conditional with Polymorphism. You can create a Null object according to the Null Object Pattern. Then make sure that the Bar property is always initialized with NullBar.

public class Foo{

    public BarClass _bar;

    public BarClass Bar{
        get{return _bar ?? new NullBar(); }
        set{ _bar = value ?? new NullBar(); } 
    } 

       public Foo(){
          Bar = new NullBar(); // initialization
       } 
    }

Then Bar will never be null.

Upvotes: 0

eglasius
eglasius

Reputation: 36035

You already answered it yourself:

As an alternative, I could do all the null checking in a ViewModel so that I've passed off something "clean" to the View.

That's it, use a ViewModel.

Upvotes: 3

Don Roby
Don Roby

Reputation: 41137

Not sure whether it really makes sense in your context, but when you are bothered by an excess of null-checks, you should contemplate the Null Object pattern.

Upvotes: 1

Rohan West
Rohan West

Reputation: 9298

You could provide lazy initialization for your navigation properties in you model. That way you could minimize the risk of encountering null values.

public class Foo
{
    private Bar _bar;

    public Bar Bar
    {
        get
        {
            if (_bar == null)
            {
                _bar = new Bar();
            }
            return _bar;
        }
    }
}

public class Bar
{
    public string Name { get; set; }
}

Upvotes: 0

Ta01
Ta01

Reputation: 31630

One option is using a helper, as described here.

Upvotes: 0

Byron Whitlock
Byron Whitlock

Reputation: 53901

Create a helper that checks for null and returns an appropriate default.

For example if you have a phone number field, you pass it the field and a constant PHONE. the helper checks if null and displays "No phone number Available" if it is null.

This way you keep all your null checking in one place.

Upvotes: 0

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