如何检查延迟加载属性是否返回null [英] How to check if a lazy loading propery returns null

问题描述

我的MVC视图具有以下代码-

My MVC view has the following code -

@foreach (var d in Model.ItineraryDays)
    {
        <tr>
            <td>
                @Html.DisplayFor(model => d.DayPlus1)
            </td>
            <td>
                @Html.ActionLink(d.Listing.Name, "Details", "Port", new { Id = d.ListingId }, null)
            </td>
            <td>
                @if (d.Listing.Port.Country != null)
                    {
                        @Html.ActionLink(d.Listing.Port.Country.Name, "Details", "Country", new { Id = d.Listing.Port.Country.Id }, null)
                    }              
            </td>

当(d.Listing.Port.Country！= null)遇到空值时，它将返回未设置为对象实例的对象引用".

When (d.Listing.Port.Country != null) encounters a null value it returns an 'Object reference not set to an instance of an object.' exception.

Port和Country都是延迟加载属性.如果'Country'！=仔细考虑，则'Port'必须有一个条目.(并非所有列表都在端口中都有一个条目，因此为空检查).

Both Port and Country are lazy loading properties. If 'Country' != mull, then 'Port' must have an entry. (Not all Listings have an entry in Port, hence the null check).

我的方法出了点问题，不确定是什么！

Something wrong with my approach, not sure what!

问候，盖伊

附录:存储库代码:

    public Itinerary GetItineraryFromId(int Id)
    {
        var itinerary = context.Itineraries
                .Include(i => i.ItineraryDays)
                .Include(i => i.ItineraryStartDates)
                .Where(i => i.Id == Id).FirstOrDefault();

        return(itinerary);
    }

• ItineraryDay具有导航.属性>>公共虚拟列表列表{设置；}
• 列表具有导航.属性>>公共虚拟端口Port {get;放;}
• 端口具有导航.属性>>公共虚拟国家(地区)国家{放;}

推荐答案

由于港口和国家/地区都是延迟加载的，因此您需要在港口级别开始有条件检查

Since both Port and Country are lazy loaded you would need to start your conditional check at the Port level

 @if (d.Listing.Port != null) {
      if (d.Listing.Port.Country != null) {
           ... Do Something
      }
 } else {
      ... Handle null scenario
 }

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