Question

//创建下面提到的类是为了解问题，而这是通过Linq2Sql创建的。

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();

问题是我得到“Nullable对象必须有值”。在上面的那一行。做了一些调试后，我觉得n.EmployerRef == employerId.Value有些麻烦，但找不到任何好的东西。

Answer 1

在我当地的游乐场，类似的案例采用这种最简单的方法：

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();
}

对你而言，这也应该有效：

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

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

Answer 2

就这样写，你不必担心空值（因为NULL == NULL等于false）

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

或者您可以保留代码并删除“.value”

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

面对Linq到sql的问题

2 个答案: