check null variable C#

Question

I have created a variable that checks if a row in a database exists. However when I put the variable in an if statement to check if it's null and the variable is null it always goes to else instead of continuing the if statement.

Is there another way of checking if a variable is null instead of == null?

var following = objCtx.Followusers.Where(c => c.User1ID == currentUser.Id || c.User2ID == cus.Id);
if (following == null)
{
    using (Html.BeginForm("Followruser", "Users"))
    {
        @Html.AntiForgeryToken()
        @Html.ValidationSummary(true)

        @Html.Hidden("Id", Id)
        <input type="submit" value="follow" class="btn btn-default" />
    }
}
else
{
    using (Html.BeginForm("unfollowruser", "Users"))
    {
        @Html.AntiForgeryToken()
        @Html.ValidationSummary(true)

        @Html.Hidden("Id", Id)
        <input type="submit" value="following" class="btn btn-default" />
    }

}

Dirk · Accepted Answer · 2014-03-14 09:22:35Z

3

The Where operator will never return null. It is also the wrong method to use if you simply want to check if a record exists. I'd use Any instead.

bool following = objCtx.Followusers.Any(
    c => c.User1ID == currentUser.Id || c.User2ID == cus.Id);

answered Mar 14, 2014 at 9:22

Dirk

11k2 gold badges38 silver badges50 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

HaukurHaf · Accepted Answer · 2014-03-14 09:21:22Z

2

Change it to:

var following = objCtx.Followusers.Where(c => c.User1ID == currentUser.Id || c.User2ID == cus.Id).SingleOrDefault();

That should return NULL if no row is found.

answered Mar 14, 2014 at 9:21

HaukurHaf

13.9k6 gold badges47 silver badges62 bronze badges

1 Comment

lastr2d2 Over a year ago

An InvalidOperationException will be thrown if there are more than one records..

Mehbube Arman · Accepted Answer · 2014-03-14 09:39:50Z

0

If you want to keep what you have given, you can also count number of values returned by the predicate.

if (following != null && following.Count < 1)

This should work for you I think.

answered Mar 14, 2014 at 9:39

Mehbube Arman

5001 gold badge7 silver badges18 bronze badges

Comments

MrFox · Accepted Answer · 2014-03-17 10:28:52Z

0

The object returned is never null, it's value might be though. Use 'FirstOrDefault()' to make the result null if there is none:

var following = objCtx.Followusers.Where(c => c.User1ID == currentUser.Id || c.User2ID == cus.Id).FirstOrDefault();

Or ask the result if it has any values:

if(following.Any())

edited Mar 17, 2014 at 10:28

answered Mar 14, 2014 at 9:24

MrFox

5,1849 gold badges48 silver badges83 bronze badges

1 Comment

Silvermind Over a year ago

The query implies a bit that there could be multiple records in the result set. it might not be so, but FirstOrDefault(...) is a better idea than SingleOrDefault(...) here.

Collectives™ on Stack Overflow

check null variable C#

4 Answers 4

Comments

1 Comment

Comments

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

1 Comment

Comments

1 Comment

Related