实体框架核心中的一对多关系

Question

I have two tables News and Comments . The Comments table has two foreign key columns UserId and NewsId .

When I get a News item by id in Entity Framework Core, comments are null.

News model class:

public partial class News
{
    public News()
    {
        NewsComments = new HashSet<NewsComments>();
        NewsLikes = new HashSet<NewsLikes>();
    }

    public int Id { get; set; }
    public string Title { get; set; }
    public string Text { get; set; }
    public string Thumbnail { get; set; }
    public string Image { get; set; }
    public DateTime? Date { get; set; }
    public int CategoryId { get; set; }
    public int PublisherId { get; set; }
    public int? ViewCount { get; set; }
    public int? LikeCount { get; set; }
    public int? CommentCount { get; set; }

    public virtual NewsCategories Category { get; set; }
    public virtual NewsPublishers Publisher { get; set; }
    public virtual ICollection<NewsComments> NewsComments { get; set; }
    public virtual ICollection<NewsLikes> NewsLikes { get; set; }
}

Comments model class:

public partial class NewsComments
{
    public int Id { get; set; }
    public int UserId { get; set; }
    public int NewsId { get; set; }
    public string Text { get; set; }
    public DateTime? Date { get; set; }
    public bool? IsAccept { get; set; }

    public virtual News News { get; set; }
    public virtual Users User { get; set; }
}

Get news method:

public News GetNews(int id)
{
    return _db.News.Find(id);
}

Answer 1

In EF if you are set by default with eager loading so you need to include the model property of the relationship like so :

public News GetNews(int id)
{
    return _db.News.Include(n=>n.NewsComments).Find(id);
}

Unless you have have forced to lazy load but still you have to setup the relationship on the context

modelBuilder.Entity<NewsComments>(entity =>
{
    entity.HasOne(nc => nc.News)
    .WithMany(n => n.NewsComments)
    .HasForeignKey(nc => nd.NewsId);
 });