Linq and DisplayFor in ASP.Net MVC

Question

I've got a model that has an ICollection of telephone numbers. In my view I want to display the value for the record that is marked as Primary.

@Html.DisplayFor(model => model.Telephones.Where(a=>a.Primary==true).Number)

The .Number is not allowed in the Linq syntax. How would one go about making the above line work or rather what is the proper way to display the number?

I probably should do the logic in the controller and put the value in a view model but it seems like this should be doable.

I feel its better to have a readonly property called PrimaryNumber inside which you can do the linq operation to fetch the Number. Then bind the displayfor to that number property. — Thanigainathan
– Thanigainathan, Commented Feb 19, 2014 at 19:11
I felt that way because the model logic should reside in Model layer — Thanigainathan
– Thanigainathan, Commented Feb 20, 2014 at 5:10

p.s.w.g · Accepted Answer · 2014-02-19 19:03:36Z

3

The Where extension method returns an IEnumerable<T>. If you just want the first item which satisfies the condition, use First:

@Html.DisplayFor(model => model.Telephones.First(a => a.Primary).Number)

If you also need to ensure that exactly one item in the set satisfies the condition (and throw an exception otherwise), consider using Single:

@Html.DisplayFor(model => model.Telephones.Single(a => a.Primary).Number)

answered Feb 19, 2014 at 19:03

p.s.w.g

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3 Comments

LB2 Over a year ago

Should be mindful of case if no number is found. I believe in that case First returns null which will cause NullRef exception. Need to handle that case.

p.s.w.g Over a year ago

@LB2 You're thinking of FirstOrDefault. First will raise an InvalidOperationException if it can't find at least one element which satisfies the condition.

Jim Wooley Over a year ago

Also, be aware that if you're using .Single, you will actually issue a Top 2 vs First which does Top 1. The only reason to use Single is if you need the exception to be thrown if more than one exists.

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