流畅的非hibernate可空外键“空引用异常”

本文关键字：引用 异常 空引用异常 hibernate | 更新日期: 2023-09-27 18:15:36

我刚刚开始使用nHibernate Fluent，我的关联都很顺利，直到我碰到一个位置，它的StateID(这是一个外键，见下文)为null。然后我得到一个错误"null reference exception"

Console.WriteLine(location。地址 + ", " + location.State.state);

: 

public static void LoadLocationsFromDatabase()
{
    using (var session = NHibernateHelper.OpenSession())
    {
        // retreive all stores and display them
        using (session.BeginTransaction())
        {
            var locations = session.CreateCriteria(typeof(Location))
                .List<Location>();
            var i = 0;
            foreach (var location in locations)
            {
                i++;
                Console.WriteLine(location.address + ", " + location.State.state);
            }
        }
    }
}
public LocationMap()
{
    Id(x => x.locationID).Column("ID");
    Map(x => x.address).Column("Address");
    References(x => x.State)
  .Column("StateID")
      .Cascade.All();
}
public class State
{
    public virtual int ID { get; set; }
    public virtual String state { get; set; }
    public virtual IList<Location> Locations { get; set; }
}

我猜这个值可能不应该在DB中为空。StateID是状态表上ID的外键，所以我猜它不应该是空的?

无论如何，我觉得我的代码应该能够允许这样或那样的方式，那么我怎么才能绕过这个呢?

流畅的非hibernate可空外键“空引用异常”

Console.WriteLine(location.address + ", " + (location.State == null ? "Unknown" : location.State.state));
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