這是我的兩個TABLE

我是採用code First來建立資料庫

這是相關的屬性

Categories

 public class Categories
    {
        public Categories()
        {
            this.Products = new HashSet<Products>();
        }
        public int Id { get; set; }
        [Column(TypeName = "nvarchar(50)")]
        public string Name { get; set; }

        public virtual ICollection<Products> Products { get; set; }
    }

Products

public class Products
    {
        public Products()
        {
            this.OrderDetails = new HashSet<OrderDetails>();
        }
        [Key]
        public int Id { get; set; }
        [Column(TypeName = "nvarchar(50)")]
        public string Name { get; set; }
        [Column(TypeName = "nvarchar(MAX)")]
        public string Description { get; set; }
        public int Category_Id { get; set; }
        [Column(TypeName = "decimal(18,2)")]
        public decimal Price { get; set; }
        [Column(TypeName = "nvarchar(300)")]
        public string PhotoUrl { get; set; }
        [Column(TypeName = "nvarchar(150)")]
        public string Author { get; set; }
        [Column(TypeName = "nvarchar(50)")]
        public string Publisher { get; set; }
        public System.DateTime PublishDT { get; set; }
        public bool IsPublic { get; set; }

        public virtual Categories Categories { get; set; }
        public virtual ICollection<OrderDetails> OrderDetails { get; set; }
    }

這是我相關的查詢方法

 public IEnumerable<Products> GetAll()
        {
            var query = (from x in _context.Products
                         join y in _context.Categories
                         on x.Category_Id equals y.Id
                         select x).ToList();           
            return query;
        }

不知道為什麼
我的Categories是null

如果我改成這樣

 public IEnumerable<Products> GetAll()
        {
            var query = (from x in _context.Products
                         join y in _context.Categories
                         on x.Category_Id equals y.Id
                         select x).ToList();
            foreach(var dto in query)
            {
                dto.Categories = FindCategories(dto.Category_Id);
            }
            return query;
        }

        private Categories FindCategories(int category_Id)
        {
            return _context.Categories.Where(x => x.Id == category_Id).FirstOrDefault();
        }

這樣反而能抓到

能否請問我錯在哪裡呢?
這是我建立的資料

更新
我好像找到原因了
我的外鍵好像是這個

想請問EFCORE那裏我該如何修改呢?
我的外鍵應該是要Category_Id才對
抱歉，我很少用code first所以問題稍微多一些也蠢一些QQ

再更
這個問題暫時用DTO處理掉
日後有機會我再回頭更新這個的解決辦法