How to check an object for null values

Question

I am using an object type variable to store a query result for binding to a drop down list. I do not want further processing on an object if it is null.

My code is :

object course;
if (GetWebsiteCurrentMode().ToLower() == "demo")
{
    course = from t in context.CourseTestDetails
            join c in context.Courses
            on t.CourseID equals c.ID                                  
            where t.UserID == UserID && c.IsDeleted == true
            select new
            {
                c.ID,
                c.CourseName
            };

}
else
{
    course = from t in context.CourseTestDetails
            join c in context.Courses
            on t.CourseID equals c.ID                                  
            where t.UserID == UserID  c.IsDeleted == false
            select new
            {
                c.ID,
                c.CourseName
            }
}
if(course !=null )
{
    ddlCourseName.DataSource = course;
    ddlCourseName.DataBind();

    ddlCourseName.Items.Insert(0, new ListItem("Select Course Name", "0"));
    ddlCourseName.SelectedValue = "0";
}
else
{
    //do something different
}

How can I check object type variable for null/empty?

I guess it would return a Empty enumerable and not null, so maybe you could check via .Any() — V4Vendetta
– V4Vendetta, Commented Apr 16, 2013 at 12:12

Habib · Accepted Answer · 2013-04-16 12:14:54Z

3

Your object course would never be null, it may or may not contain record. Since you are getting the results back in object, you should cast it to IEnumerableand useAny` to see if it contains record. You can try:

if ((course as IEnumerable<object>).Any())
{
    //records found
}
{
    //no record found
}

answered Apr 16, 2013 at 12:14

Habib

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5 Comments

Habib Over a year ago

@Serge, yes. It may be better to cast it to a separate variable and check if its not null (to see if the casting succeeded) , but the whole point is to cast it to IEnumerable<T> and then use Any

Serge Over a year ago

Is using Any more relevant than using Count()?

V4Vendetta Over a year ago

@Habib was just wondering about the cast to IEnumerable<object>, don't think object would be right candidate but then maybe i am wrong please do let me know if i am missing something

Habib Over a year ago

@Serge, yes see: stackoverflow.com/questions/305092/…

Habib Over a year ago

@V4Vendetta, the only reason I used casting to object is that the OP is projecting to anonymous type,

Satpal · Accepted Answer · 2013-04-16 12:16:43Z

2

if (course != null && (course as IEnumerable<object>).Any())
{
}

Optional: Additionally you should also check that object is implements IList interface

if (course  is IList)
{

}

answered Apr 16, 2013 at 12:16

Satpal

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Comments

Community · Accepted Answer · 2017-05-23 10:25:42Z

The queries are not null but empty. But since you're using an object you cannot use Enumerable.Empty. You can use following trick from E. Lippert to get one inferred-typed variable for multiple IEnumerable<anynymous type>:

Use this method to create a typed variable from an anonymous type:

static IEnumerable<T> SequenceByExample<T>(T t){ return null; }

Now this works:

var course = SequenceByExample(new { ID = 0, CourseName = "" } );
if (GetWebsiteCurrentMode().ToLower() == "demo")
{
    course = from t in context.CourseTestDetails
            join c in context.Courses
            on t.CourseID equals c.ID                                  
            where t.UserID == UserID && c.IsDeleted == true
            select new
            {
                c.ID,
                c.CourseName
            };
}
else
{
    course = from t in context.CourseTestDetails
    // ...
}
if(course.Any())
{
   // ...
}
else
{
    //do something different
}

Declaring an implicitly typed variable inside conditional scope and using it outside

Here's a simple example to demonstrate that it works: http://ideone.com/lDNl4d

Serge · Accepted Answer · 2013-04-16 12:32:29Z

0

var course = from t in context.CourseTestDetails
                 join c in context.Courses
                 on t.CourseID equals c.ID                                  
                 where t.UserID == UserID && c.IsDeleted == (GetWebsiteCurrentMode().ToLower() == "demo")
                 select new
                 {
                     c.ID,
                     c.CourseName
                  };

if (course.Any()) ...

edited Apr 16, 2013 at 12:32

answered Apr 16, 2013 at 12:19

Serge

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