Check null in Entity framework - entity-framework

Question

string password = Infoware.Students.FirstOrDefault(x=>x.AdmissionNo == AdmissionNo && x.AdmissionNo != null).Password;
Here students is a table where I have AdmissionNo and Password columns, Need to get password if admissionNo exists in the table. This expression is fetching Password for given AdmissionNo if the admissionNo is present in the records but if the entered admissionNo is not found in the records then it throwing NullReference Exception.
How can I check that given AdmissionNo is not a Valid AdmissionNO ??

Answer 1

You can simply check for null using an if statement"
if ( AdmissionNo != null )
{
//your code
}
You can also check ObjectContextOptions.UseCSharpNullComparisonBehavior Property which was introduced in EF 5.0

Answer 2

You can check it using Any:
.Any(a => a.AdmissionNo == null)
Or using if statement:
string user = Infoware.Students.FirstOrDefault(x=>x.AdmissionNo == AdmissionNo && x.AdmissionNo != null);
if(user != null)
{
password = user.Password;
}

Answer 3

You just need to put your tests the other way around (as they will shortcut):
string password = Infoware.Students.FirstOrDefault(x=> x.AdmissionNo != null
&& x.AdmissionNo == AdmissionNo ).Password;
And re-reading your question, you issue is when nothing is found...
So:
string password;
var result = Infoware.Students.FirstOrDefault(x=> x.AdmissionNo != null
&& x.AdmissionNo == AdmissionNo );
if (result != null) {
password = result.Password;
}