ASP.NET MVC-无法在对象中插入重复的键行

Question

我有一个实体框架核心的问题。我有2个模型：category.cs

    public int Id { get; set; }
    [DisplayName("Category | ")]
    [Required(ErrorMessage = "Category Name is Required")]
    public string CategoryName { get; set; }

和LibraryItem.cs

    public int Id { get; set; }

    [DisplayName("Category Id")]
    [Required(ErrorMessage = "Category Id is Required")]
    public int CategoryId { get; set; }

    public Category Category { get; set; }
    [Required(ErrorMessage = "Title is Required")]
    public string Title { get; set; }

    [DisplayName("Author, Speaker or Director")]
    [Required(ErrorMessage = "Creator of the media is required")]
    public string Author { get; set; }

    public int? Pages { get; set; }

    [DisplayName("DVD or Audiobook Length")]
    public int? RunTimeMinutes { get; set; }

    [DisplayName("Available to borrow")]
    public bool IsBorrowable { get; set; }

    [DisplayName("Name of Borrower")]
    public string Borrower { get; set; }

    [DisplayName("Date of the Borrow")]
    public DateTime? date { get; set; }

    [DisplayName("Type of Media")]
    [Required(ErrorMessage = "Type of Media is Required")]
    public string Type { get; set; }

LibraryItem有一个外键CategoryId，它是Category表的主键。我想用相同的外键添加两个项目。所以这两个项目属于同一类别。但当我尝试添加具有相同CategoryId的另一个时，会出现以下错误

cannot insert duplicate key row in object

有人知道是什么导致了这个问题吗？多谢！

Answer 1

您必须通过在每个类上添加导航属性,让EF知道这两个实体以一对多的关系相关：

    public class Category {
        ...
        
        public virtual ICollection<LibraryItem> LibraryItems {get; set;}
    }


    public class LibraryItem {
        ...
        
        [DisplayName("Category Id")]
        [Required(ErrorMessage = "Category Id is Required")]
        public int CategoryId { get; set; }

        public Category Category { get; set; }
    }

如果添加了导航属性，则可以使用Fluent API手动配置DbContext的OnModelCreating方法中的关系

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<LibraryItem>()
            .HasOne(l => l.Category)
            .WithMany(c => c.LibraryItems);
    }

Answer 2

问题是您创建了一对一的关系，但您需要一对多

您必须修复您的类别类：

    public int Id { get; set; }
    [DisplayName("Category | ")]
    [Required(ErrorMessage = "Category Name is Required")]
    public string CategoryName { get; set; }

    [InverseProperty(nameof(Library.Category))]
    public virtual ICollection<LibraryItem> LibraryItems {get; set:}

修复后，您将不得不再次进行迁移