在 EF Core ASP.NET Core Razor Pages .NET6 中插入自动生成的桥 table

Question

我是 EF 的新手，需要帮助来理解以下内容：我在数据库中有一个 Class table 和一个学生 table。一个 Class 可以有很多学生，一个学生可以在很多 class 中。我有一个由 EF 核心自动生成的 table，名为 ClassModelStudent。它有以下字段：

我创建了一个 razor 页面来创建 class 并且在 post 事件中，按钮应该发送 ClassID 并重定向到 AddStudents 页面。

以下是 AddStudents Class 的代码：

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using TestProject.Model;

namespace TestProject.Pages.Classes
{
    public class EnrollmentModel : PageModel
    {
        private readonly TestProject.Data.TestProjectContext _context;

    public EnrollmentModel(TestProject.Data.TestProjectContext context)
    {
        _context = context;
    }
    [BindProperty]
   public Enrollment Enrollments { get; set; }   
    public SelectList Classes { get; set; }    
    public IList<Student> UserProfile { get; set; }
    [BindProperty(SupportsGet = true)]
    public string? SearchString { get; set; }
    public async Task OnGetAsync()
    {
        var students = from s in _context.User_Profile
                       select s;
        if (!string.IsNullOrEmpty(SearchString))
        {
            students = students.Where(s => s.FirstName.Contains(SearchString));
        }

        UserProfile = await students.ToListAsync();

        var classes = from i in _context.Class
                          orderby i.Description
                          select i;

        Classes = new SelectList(classes, "ClassID", 
"Description");

    }

    public async Task<IActionResult> OnPostAsync()
    {
        if (!ModelState.IsValid)
        {

            return Page();
        }
       //THIS IS WHERE I TRIED ACCESSING CLASSMODELSTUDENT TABLE 
      //AND THE CONTEXT DID NOT SEE IT
       // _context.e
        await _context.SaveChangesAsync();

        return RedirectToPage("./Index");
    }
}

}

我目前已将其连接到注册 table。我什至不确定是否应该将其写入自动生成的 table ClassModelStudents 或手动创建的注册？注册 table 如下所示：

在 AddStudents 页面中，我显示了 table 中的学生列表。我在 table 的每一行中创建了 'Add To Class' 按钮。我想在单击 'add to class' 按钮时将该学生添加到选定的 class。我应该写信给 ClassModelStudents table。请看下面的AddStudents页面截图：

我不明白的是如何为 ClassModelStudent 创建 class（模型）？因为我无法使用上下文直接访问此 table。如何访问此 table 以将 ClassID 和 StudentID 写入其中？

请指教.. 非常感谢您的帮助..

以下是我的模型 class for ClassModel:

 public class ClassModel

{
    [Key]
    [Required]
    [Display(Name ="Class ID")]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ClassID { get; set; }
    //[ForeignKey("UserProfile")]
    //[Display(Name = "User ID")]
    //public virtual int ID { get; set; }
    [Required]
    public string Description { get; set; } 
    [Required]
    public int Occurence { get; set; }
    [Required]
    [DataType(DataType.Date)]
    public DateTime Startdate { get; set; }
    [Required]
    [DataType(DataType.Time)]
    public DateTime From { get; set; }
    [Required]
    [DataType(DataType.Time)]
    //[GreaterThanOrEqualTo("From")]
    public DateTime To { get; set; }
    [Required]
    [DataType(DataType.Currency)]
    public double Fees { get; set; }

    [DisplayFormat(NullDisplayText = "No Instructor Assigned")]
    [ForeignKey("InstructorID")]
    public virtual int InstructorID { get; set; }
    public Instructor? Instructor { get; set; }

    [DisplayFormat(NullDisplayText = "No Student Assigned")]
    public ICollection<Student>? Students { get; set; }

    public ICollection<Enrollment>? Enrollment  { get; set; }
}

这是注册 class 型号：

public class Enrollment
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int EnrollmentID { get; set; }
    [Required]

    [ForeignKey("ClassID")]
    public virtual int ClassID { get; set; }
    [Required]
    [ForeignKey("StudentID")]
    public virtual int StudentID { get; set; }
    [Required]
    public ClassModel? Class { get; set; }
    [Required]
    public Student? Student { get; set; }

    

}

以下是学生模型：

public class Student
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Display(Name = "StudentID")]
    public int StudentID { get; set; }
    [Required]
      
    public string FirstName { get; set; }

    [Required]

    public string LastName { get; set; }
   
    
    [Required]
    public Boolean Status { get; set; }
    [DataType(DataType.Date)]
    public DateTime DateOfBirth { get; set; }
    [Required]
    [DataType(DataType.EmailAddress)]
    public string Email { get; set; }
    [Required]
    [Phone]
    [DataType(DataType.PhoneNumber)]
    public string PhoneNumber { get; set; }

    public string EmergencyContactName { get; set; }
    [Phone]
    [DataType(DataType.PhoneNumber)]
    public string EmergencyContactNumber { get; set; }

    [Required]
    public string Gender { get; set; }

    public string FullName
    {
        get { return LastName + ", " + FirstName; }
    }
    [DisplayFormat(NullDisplayText = "No Class Assigned")]
    public ICollection<ClassModel>? Classes { get; set; }

    public ICollection<Enrollment>? Enrollments { get; set; }    
}

我没有 ClassModelStudent 的代码，因为它是自动生成的。

Answer 1

当你在 TestProjectContext 中创建 many-to-many 关系时，你是否像这样编写代码：

    .......

    public Dbset<Class> classes;
    public Dbset<students> students;

ClassModelStudenttable是EF core自动生成的，所以不能用_context.ClassModelStudent插入任何数据？

如果你的问题像我上面提到的那样，你可以使用另一种方法来创建many-to-many关系，我写了一个简单的演示：

型号

 public class Group
    {
        public int Id { get; set; }
        public string GroupName { get; set; }
        public List<GroupMembers> GroupMembers { get; set; }
    }

public class User
    {
        public int Id { get; set; }
        public string UserName { get; set; }
        public List<GroupMembers> GroupMembers { get; set; }
    }

public class GroupMembers
    {
        public int Id { get; set; }
        public int UserId { get; set; }
        public User user { get; set; }

        public int GroupId { get; set; }
        public Group group { get; set; }
    }

DataContext

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

        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<GroupMembers>()
                .HasKey(gm => new { gm.UserId, gm.GroupId });
            modelBuilder.Entity<GroupMembers>()
                .HasOne(gm => gm.group)
                .WithMany(group=> group.GroupMembers)
                .HasForeignKey(gm => gm.GroupId);
            modelBuilder.Entity<GroupMembers>()
                .HasOne(gm => gm.user)
                .WithMany(user => user.GroupMembers)
                .HasForeignKey(gm => gm.UserId);
        }
        public DbSet<User> usertable { get; set; }
        public DbSet<Group> grouptable { get; set; }
        public DbSet<GroupMembers> GroupMembers { get; set; }
    }

通过这种方式在 DataContext 中创建多对多关系，您可以在 pagemodel 中使用 _context.(Relational tables)。

============================================= ==============

如果Enrollment table是ClassModel和Student的Relational table，则不需要让EF core创建其他关系table.

型号

public class ClassModel
    {
        [Key]
        public int ClassID { get; set; }
        public string Description { get; set; }
        public string ClassName { get; set; }
        
        public ICollection<Enrollment>? Enrollments { get; set; }
    }

public class Enrollment
    {
        [Key]
        public int EnrollmentID { get; set; }
        

        [ForeignKey("ClassID")]
        public virtual int ClassID { get; set; }
        [Required]
        [ForeignKey("StudentID")]
        public virtual int StudentID { get; set; }
        [Required]
        public ClassModel? Class { get; set; }
        [Required]
        public Student? Student { get; set; }
    }

public class Student
    {
        [Key]
        public int StudentID { get; set; }
        public string FirstName { get; set; }
        public string Email { get; set; }

        public ICollection<Enrollment>? Enrollments { get; set; }
    }

TestProjectContext

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

        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Enrollment>()
                .HasKey(gm => new { gm.ClassID, gm.StudentID });
            modelBuilder.Entity<Enrollment>()
                .HasOne(gm => gm.Class)
                .WithMany(group => group.Enrollments)
                .HasForeignKey(gm => gm.ClassID);
            modelBuilder.Entity<Enrollment>()
                .HasOne(gm => gm.Student)
                .WithMany(user => user.Enrollments)
                .HasForeignKey(gm => gm.StudentID);
        }

        public DbSet<ClassModel> ClassModels { get; set; }
        public DbSet<Student> students { get; set; }
        public DbSet<Enrollment> enrollments { get; set; }
    }

那么，你只有三个tables

您可以在 PageModel 中使用它们中的任何一个

在 EF Core ASP.NET Core Razor Pages .NET6 中插入自动生成的桥 table

Insert to autogenerated Bridge table in EF Core ASP.NET Core Razor Pages .NET6

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