c# - .NET Core 2.0 - 来自 BlogItem 的 BlogCategory

Question

只是想让我的 @item.BlogCategories.CategoryName 显示类别，但它说对象未设置。我检查了数据库。 BlogCategoryId 是正确的。如果这是 MVC5，那将不是问题。 MVC 核心有什么不同？

它写入其余的 @items 正确，@item.Title，id 等。

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NullReferenceException: Object reference not set to an instance of an object.

<a href="#">@item.BlogCategories.CategoryName</a>

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public class BlogItem
{
    public int Id { get; set; }
    public string Title { get; set; }
    [MaxLength(100)]
    [Required]
    public string BodyText { get; set; }
    public string Image { get; set; }
    public DateTime DateCreated { get; set; }
    public int Views { get; set; }
    public string UserId { get; set; }
    public virtual ApplicationUser User { get; set; }

    public virtual IEnumerable<ImageTag> Tags { get; set; }

    public int BlogCategoryId { get; set; }
    public virtual BlogCategory BlogCategories { get; set; }
}

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    private readonly BlogDbContext db;

    public HomeController(BlogDbContext context)
    {
        db = context;
    }
    #endregion
    public IActionResult Index()
    {
        List<BlogItem> bi = db.BlogItems.OrderByDescending(m => m.DateCreated).ToList();
        return View(bi);
    }

Answer 1

Entity Framework Core 不执行延迟加载(至少 not yet )，因此您需要明确说明所需的子属性。例如:

List<BlogItem> bi = db.BlogItems
    .Include(bi => bi.BlogCategory)
    .OrderByDescending(m => m.DateCreated)
    .ToList();