I'm trying to get a property from an array of object that can be null (the array) and I'm always getting a null reference exception.
How can I tell LINQ to not process it in case it's null or to return an empty string?
foreach (Candidate c in candidates) {
results.Add(new Person
{
firstName = c.firstname, //ok
lastName = c.Name, //ok
// contactItems is an array of ContactItem
// so it can be null that's why I get null exception
// when it's actually null
phone = c.address.contactItems.Where( ci => ci.contactType == ContactType.PHONE).First().contactText
}
);
}
I've also tried that to not take null. I don't get the mechanism to tell LINQ not to process if the array is null.
phone = c.address.contactItems.Where( ci => ci != null && ci.contactType == ContactType.PHONE).First().contactText
Select(q => { var attendanceList = new AttendanceBAL(). GetAttendanceListOf(q. _RollNumber); if (attendanceList == null) return null; return new StudentRecords() { _RollNumber = q. _RollNumber, _Class = q.
It will return an empty enumerable. It won't be null.
If you have a Query that returns a empty set then ToList returns null. You would probably expect it to return an empty list (Count = 0), which is the case when using data providers for SQL Server.
You can check if it's null
with ?:
(conditional) operator:
phone = c.address.contactItems == null ? ""
: c.address.contactItems.Where( ci => ci.contactType == ContactType.PHONE).First().contactText
If First
throws an exception because there's no one with ContactType.PHONE
you can use DefaultIfEmpty
with a custom default value:
c.address.contactItems.Where( ci => ci.contactType == ContactType.PHONE)
.DefaultIfEmpty(new Contact{contactText = ""})
.First().contactText
Note that First
now cannot throw an exception anymore since i've provided a default value.
Try the code below (I've assumed that contactText
is a string
).
You may want to look at standardising the capitalisation of your public property names to all start with an upper-case letter.
foreach (Candidate c in candidates) {
string contactText =
c.address.contactItems
.Where(ci => ci.contactType == ContactType.PHONE)
.Select(ci => ci.contactText)
.FirstOrDefault()
results.Add(
new Person
{
firstName = c.firstname,
lastName = c.Name,
phone = contactText ?? string.Empty
});
}
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