如何在 ASP.NET 核心 MVC 代码优先方法中的多个 table 中添加外键？

Question

ApplicationDbContext.cs

public class ApplicationDbContext : DbContext
{
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
        {
        }

        public DbSet<BookReadingEvent> BookReadingEvents { get; set; }
        public DbSet<Register> RegisterAccount { get; set; }
        public DbSet<Login> LoginAccount { get; set; }
}

注册模型class:

namespace BookReadingEvents.Models
{
    [Index(nameof(Email), IsUnique = true)]
    public class Register
    {
        [Key]
        public int RegisterId { get; set; }

        [Required]
        [DataType(DataType.EmailAddress, ErrorMessage = "Please enter a valid e-mail address")]
        public string Email { get; set; }
        [Required]
        [Display(Name = "Full Name")]
        public string Name { get; set; }
        [Required]
        [DataType(DataType.Password)]
        [MinLength(5, ErrorMessage = "Password length cannot be less than 5")]
        public string Password { get; set; }

        [NotMapped] // Does not affect the database
        [Compare("Password")]
        [Required]
        [DataType(DataType.Password)]
        [Display(Name = "Confirm Password")]
        public string ConfirmPassword { get; set; }
    }
}

登录模式class:

public class Login
{
        [Key]
        public int LoginId { get; set; }
        
        [Required]
        [DataType(DataType.EmailAddress, ErrorMessage = "Please enter a valid e-mail address")]
        public string Email { get; set; }
        
        [Required]
        [DataType(DataType.Password)]
        [MinLength(5, ErrorMessage = "Password length cannot be less than 5")]
        public string Password { get; set; }

        public DateTime EntryDate { get; set; } = DateTime.Now;

        [ForeignKey("Registers")]
        public int RegisterId { get; set; }
        public virtual Register Registers { get; set; }

        // Here foreign key is working fine
}

读书活动模型class：

public class BookReadingEvent
{
    [Key]
    public int Id { get; set; }
    [Required]
    public string Title { get; set; }

    [Required]
    [DataType(DataType.Date)]
    public DateTime Date { get; set; }

    [Required]
    public string Location { get; set; }
    public string StartTime { get; set; }
    public string EventType { get; set; }

    [Range(1,9999)]
    public int Duration { get; set; }

    [StringLength(50, ErrorMessage = "Description length can't be more than 50.")]
    public string Description { get; set; }

    [StringLength(500, ErrorMessage = "Other Details length can't be more than 500.")]
    public string Details { get; set; }

    public string InviteByEmail { get; set; }

    [ForeignKey("Registers")]
    public int RegisterId { get; set; }
    public virtual Register Registers { get; set; }
       
    // Error: The ALTER TABLE statement conflicted with the FOREIGN KEY constraint 
    // "FK_BookReadingEvents_RegisterAccount_RegisterId". The conflict occurred in database 
    // "BookReadingEvents", table "dbo.RegisterAccount", column 'RegisterId'.
}

我也想将外键 RegisterId 添加到 BookReadingEventModel 中，但是当它在 Login 模型上正常工作时出现错误。如何使用代码优先方法将外键添加到读书事件 table？

Answer 1

如果您的数据库中有数据与您的更改相冲突，则会导致此错误。通过创建一个全新的迁移并运行它在一个新的空数据库上，可以很容易地对其进行测试。

您的数据库中很可能有无法引用的旧测试数据。

Answer 2

您在多个表中需要 RegisterId，这会导致错误。尝试使 RegisterId 在 classes

中都可以为空

        public int? RegisterId { get; set; }

        [ForeignKey("RegisterId")]
        public virtual Register Register { get; set; }

并将导航属性也添加到寄存器 class

public class Register
{
        [Key]
        public int RegisterId { get; set; }
         ....

      [InverseProperty(nameof(Login.Register))]
       public virtual ICollection<Register> LoginRegisters {get; set;}

       [InverseProperty(nameof(BookReadingEvent.Register))]
       public virtual ICollection<Register> BookReadingEventRegisters {get; set;}

}

如何在 ASP.NET 核心 MVC 代码优先方法中的多个 table 中添加外键？

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