使用 Linq 时出现“System.NullReferenceException”错误

Question

I'm trying to learn one to many relations with EF Core.

In summary: I have two tables; Artists and Songs.

But when I try to reach songs which belongs that artist I am getting error.

Why I'm getting null reference error?

Answer 1

您必须手动将所需的相关实体包含在列表中，如下所示包含歌曲：

var theArtist = DB.Artists.Include("Songs").FirstOrDefault(a => a.ID==1);