Facing problem in Linq to sql

//Below mentioned class is created to understand the proble开发者_开发百科m, while this is created through Linq2Sql.

public class JobAds
{
 public int ID  { get; set; }
 public int EmployerRef { get; set;}
}

int? employerId = null;

var jobAdListing = JobAds.Where 
     ( n => (!employerId.HasValue || n.EmployerRef == employerId.Value )).ToList();

The Issue is I'm getting "Nullable object must have a value." at the above line. After doing some debugging, I feel n.EmployerRef == employerId.Value is making some trouble, but unable to find anything good.

Just write liks this, you don't have to worry about the null values (since NULL == NULL equals false)

int? employerId = null;
var jobAdListing = tblCompanies.Where 
     (n => (n.fkUserID_responsible == employerId)).ToList();

Or you can keep your code and just remove the ".value"

var jobAdListing = JobAds.Where 
     ( n => (!employerId.HasValue || n.EmployerRef == employerId)).ToList();

in my local playground a simmilar case works with this easiest approach:

using (UnitOfWork.Begin("LinqToSql"))
{
    Guid? id1 = null;
    Guid? id2 = this.personRepository.GetAll().First().FavouriteProjectId;

    var all = this.personRepository.GetAll().Where(o => o.FavouriteProjectId == id1 || o.FavouriteProjectId == id2).ToArray();
}

for you, this should work too:

int? employerId = null;
int? employerType = null; /* OTHER Conditions */

var list = JobAds.Where(n => n.EmployerRef == employerId &&
                             n.EmployerTypeRef == employerType)).ToArray();