Conditional not working in ASP.NET Core 7 Razor view

Question

I have a search function on my site, and one of the options the user has is to select the type of search.

So given this example in a view:

@using System.Data
@model DataSet

hello, world
<br />
@ViewData["searchtype"]

@if (ViewData["searchtype"] == "rank")
{
    <h2>Ranks</h2>
    <ol>
        @foreach (DataRow dr in Model.Tables[0].Rows)
        {
            <li>@dr["name"].ToString()</li>
        }
    </ol>
}

I would expect it to either give me the header Ranks by itself (if the datatable is empty) or a numbered list of ranks following that header.

What I get instead is this:

hello, world
rank

So I know that it's getting to the view. And I know that it's able to see the value of the ViewData["searchtype"]. But the conditional, which should be evaluated as true, is not.

And I know that the obvious answer is for ViewData["searchtype"] to be changed to ViewData["searchtype"].ToString(), but when I do that, I get literally nothing. No "hello, world", no "rank", no "Rank", and nothing from the _Layout page, either. Just a pristine blank browser.

Also, I'm aware that using a DataSet as a model instead of an object is not optimal, but the data tables generated differ depending on the search type, so I'm stuck with that.

Answer 1

To expand on @Jackdaw's answer, Microsoft's pattern matching documentation for the is operator lists:

C# supports multiple patterns, including declaration, type, constant, relational, property, list, var, and discard.

Under the section Constant pattern:

You use a constant pattern to test if an expression result equals a specified constant. ... you can use any constant expression, such as ... an integer or floating-point numerical literal, a string literal, a Boolean value true or false, ...

In your post, you're comparing against the string literal "rack" so you can set your if condition to:

@if (ViewData["searchtype"] is "rank")
{
    ...
}

As the comments (see @ProgrammingLlama's comment) and answer (from @Akade) in this SO post emphasizes, ensure the use of a string literal versus a string variable.

If the "searchtype" key is not in the ViewData dictionary or the key is in the dictionary but its value is explicitly set to null, or the "searchtype" key/value pair is some other value, then the if condition above evaluates to false.

@Jackdaw's answer uses the is operator to match an expression against the pattern listed under the section Declaration and type patterns:

When a declaration pattern matches an expression, that variable is assigned a converted expression result