How to check null value in MVC view?

Question

Hi,

I am using MVC with LINQ-to-SQL class.

as foreign key can be null, i have one record having f.k. null and others are having values.

now i am displaying it in view by Index view.

In index view i am resolving f.k. by writing code like

<%= Html.Encode(item.UserModified.UserName) %>

Now i have a problem in view that "object reference is not set".

And this is because of we are having null value in one of the f.k. field!

so can i write code in view to check whether Associated object pointing to null or nothing?

Answer 1

With C#, you can use the conditional operator:

<%= Html.Encode(item.UserModified == null ? "" : item.UserModified.UserName) %>

However, it might be a better choice to move the UserName property to be a direct child of item, or to put it in ViewData.

Answer 2

You can write any code you want in the view if necessary, so you could do:

<%= Html.Encode(item.UserModified.UserName ?? string.Empty) %>

You could also make a HtmlHelper extension to do this:

public string SafeEncode(this HtmlHelper helper, string valueToEncode)
{
    return helper.Encode(valueToEncode ?? string.Empty);
}

You could then simply do:

<%= Html.SafeEncode(item.UserModified.UserName) %>

Of course if it's UserModified that's null and not UserName then you'll need some different logic.

Answer 3

First consider whether in your model an instance of User is valid without Name. If no then you should put a guard clause in the constructor.

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.

This will make sure that you do not have to check for Null everywhere.