mvc 4 IEnumerable checking if its null

Question

I've looked about on stackoverflow for this but can't find the answer I'm looking for, its simple really. Basically I want to know how to check if my IEnumerable variable is null, my if statement just laughs at me and lets the variables pass.

Here's the scenario, I have a list of data pulled from the database, this little bit is a filter function (so no [HttpPost]) that filters the content based on user input. The first thing it checks is the review list in the review database, if this returns empty I want it to check the user list in the review database.

here's the code:

   var review = from m in _db.Reviews
                     select m;        

        if (!String.IsNullOrEmpty(searchString))
        {
            review = review.Where(s => s.review.Contains(searchString));
            if (review != null && review.Any())
            {
                return View(review);      
            }
            else
            {
                review = review.Where(s => s.user.Contains(searchString));
                return View(review);      
            }

I've messed about with it a bit, the if statement used to check if it was null, then .any(), then != null and now both, the variable just walks on by, laughing as it goes. I ran debugger and put it on a few spots. When I input a value that I know will not return results this is what the debugger says the review value is:

"IEnumerable did not yield any results"

In a pathetic attempt to prevent this I even chucked that sentence in the if statement. the variable laughed so hard I swear I could hear it through my speakers.

Anyways guys, if I could get the best way to do this, and why. There will be cookies.

Answer 1

The problem is that when you say this:

         review = review.Where(s => s.user.Contains(searchString));

... you're not modifying the original query:

 var review = from m in _db.Reviews
              select m;        

But rather, the one you create here:

        review = review.Where(s => s.review.Contains(searchString));

So effectively you're saying:

If the query doesn't have any results, add additional criteria to it.

This will obviously not yield any results either.

Try this instead:

    if (!String.IsNullOrEmpty(searchString))
    {
        var reviewMatches = _db.Reviews.Where(s => s.review.Contains(searchString));
        if (reviewMatches.Any())
        {
            return View(reviewMatches);      
        }
        else
        {
            var userMatches = _db.Reviews.Where(s => s.user.Contains(searchString));
            return View(userMatches);      
        }

Note that the way you're declaring your variables, it's impossible for them to be null, so you only have to worry about whether they are empty.