Question

我在尝试从导航属性中获取数据时收到NullReferenceException。

我正在尝试将 JSon 显示为导航属性＆＃39; EventImage＆＃39;中的数据。即使元素在属性内部并且所有内容都被引用，我也会得到null引用异常。我查询了数据库，得到了预期的结果，但是当我调用控制器的[get]动作方法时，只出现空引用异常。我猜即使没有合适的元素，并且由于一对一或一对一的关系，我应该实现＆＃39; EventImage：null＆＃39;作为JSon的结果。

域名模式：

public class EventDetail
{
    [DatabaseGenerated(DatabaseGeneratedOption.None), Key, ForeignKey("Event")]
    public int EventDetailId { get; set; }

    [DisplayFormat(NullDisplayText = "No information")]
    public string EventLocalization { get; set; }

    [DataType(DataType.Date),
     DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true,
         NullDisplayText = "No information")]
    public DateTime? EventDate { get; set; }

    [DisplayFormat(NullDisplayText = "No information")]
    public string EventDescription { get; set; }

    public virtual EventImage EventImage { get; set; }
    public virtual Event Event { get; set; }

    public virtual ICollection<EventPrice> EventPrices { get; set; }
}

public class EventImage
{
    [DatabaseGenerated(DatabaseGeneratedOption.None), Key, ForeignKey("EventDetail")]
    public int EventImageId { get; set; }

    public string EventImageBase64 { get; set; }

    public virtual EventDetail EventDetail { get; set; }
}

逻辑模型：

public class SingleEventDetail
{
    public int EventDetailId { get; set; }

    public string EventLocalization { get; set; }

    public DateTime? EventDate { get; set; }

    public string EventDescription { get; set; }

    public string EventImage { get; set; }
}

public class EventImage
{
    public int EventImageId { get; set; }

    public string EventImageBase64 { get; set; }
}

方法I调用内部控制器

public override SingleEventDetail GetById(int id)
    {
        var eventDetail = _eventDetailRepository.GetAll().Select(e => new SingleEventDetail
        {
            EventDetailId = e.EventDetailId,
            EventDate = e.EventDate,
            EventLocalization = e.EventLocalization,
            EventDescription = e.EventDescription,
            EventPrices =
                _eventDetailRepository.GetById(id)
                    .EventPrices.Select(ep => new EventPriceForSingleEventDetail
                    {
                        Amount = ep.Amount,
                        Currency = ep.Currency,
                        IsFullPrice = ep.IsFullPrice
                    }).ToList(),
            EventImage = e.EventImage.EventImageBase64
        }).SingleOrDefault(e => e.EventDetailId == id);

        return eventDetail;
    }

_eventDetailRepository.GetAll（）

public IEnumerable<EventDetail> GetAll()
    {
        return _context.EventDetail.ToList();
    }

_eventDetailRepository.GetById（int id）

public EventDetail GetById(int id)
    {
        return _context.EventDetail.ToList().SingleOrDefault(c => c.EventDetailId == id);
    }

Answer 1

我找到了解决方案。延迟加载不适用于这个特定的'EventImage'导航属性，但我不知道为什么。我已经将方法_eventDetailRepository.GetById（int id）更改为具有eager loagind的方法，现在一切正常。

public EventDetail GetById(int? id)
    {
        return _context.EventDetail.Include(e => e.EventPrices).Include(e => e.EventImage).SingleOrDefault(e => e.EventDetailId == id);
    }

从web-api 2中的navigation属性获取数据时出现NullReferenceException

1 个答案: