Question

I have a model where Person has 0, 1 or 2 Contact objects.
Contact information home (contact_type is “h”) and contact information for work (contact_type is “w”).

Is there a way to check that the Contact object with contact_type == "h" exists when selecting street name? Right now I’m getting a null exception if the Contact object does not exist.

from m in persons
select new
{
    Id = m.id,
    Name = m.surname,
    Address = m.Contacts.Where(c => c.contact_type == "H").SingleOrDefault().streetname
};

Answer 1

How about:

var rows = from m in persons
    let h = m.Contacts.Where(c => c.contact_type == "H").SingleOrDefault()
    select new {
        Id = m.id,
        Name = m.surname,
        Address = (h == null ? null : h.streetname)
    };

or:

var rows = from m in persons
    select new {
        Id = m.id,
        Name = m.surname,
        Address = m.Contacts.Where(c => c.contact_type == "H")
                 .Select(c => c.streetname).SingleOrDefault()
    };

which could also be written (perhaps more clearly):

var rows = from m in persons
    select new {
        Id = m.id,
        Name = m.surname,
        Address = (from c in m.Contacts
                   where c.contact_type == "H"
                   select c.streetname).SingleOrDefault()
    };