EF Core 在多对多表中插入

Question

我用 Razor Pages 搭建了我的用户模型，并在创建页面上我想在联结表 UserRoles 上插入用户角色。

这是我的模特

[Table("Users")]
public class User
{
    public User()
    {
        IsActivo = true;          
    }

    public int Id { get; set; }

    [Required]
    [Display(Prompt = "Username")]
    public string Username { get; set; }
    [Display(Name = "Último Acesso")]
    public DateTime? DataSessao { get; set; }
    [Display(Name = "Activo")]
    public bool IsActivo { get; set; } 
    public Colaborador Colaborador { get; set; }

    public ICollection<UserRoles> UserRoles { get; set; }
}

这是创建模型

public class CreateModel : PageModel
{
    private readonly HutIS.Models.HutISContext _context;

    public CreateModel(HutISContext context)
    {
        _context = context;
    }

    public IActionResult OnGet()
    {
        DepartamentosOptions = _context.Departamento.Select(d =>
              new SelectListItem
                  {
                       Value = d.Id.ToString(),
                       Text = d.Nome
                  }).ToList();


        RolesOptions = _context.Roles.Select(d =>
                  new SelectListItem
                      {
                         Value = d.Id.ToString(),
                         Text = d.Type
                       }).ToList();

        return Page();
    }

    [BindProperty]
    public User User { get; set; }
    public List<SelectListItem> DepartamentosOptions { get; set; }
    public List<SelectListItem> RolesOptions { get; set; }

    public async Task<IActionResult> OnPostAsync()
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        _context.User.Add(User);

        await _context.SaveChangesAsync();

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

在 html 上

<div class="form-group">
    <label asp-for="User.UserRoles" class="control-label"></label>
    <select asp-for="User.UserRoles" asp-items="Model.RolesOptions" class="form-control form-control-sm">
        <option value="">Selecione um Departamento...</option>
    </select>
    <span asp-validation-for="User.UserRoles" class="text-danger"></span>
</div>

我不确定我该怎么做，当然我在这里遇到了一个异常，但是如果它是 User 中的一个集合，我该如何绑定 UserRoles 呢？

编辑

我解决了异常问题，它与模型属性有关。现在的问题是 UserRoles 表上没有插入任何内容，我不太确定这样做的方法是什么，因为与 Departments 不同，它的 User 没有 UserRoles 的导航属性。

你可以看到关系是正确的

Answer 1

对于<select multiple="multiple" asp-for="User.RoleIds" asp-items="Model.RolesOptions" class="form-control form-control-sm">，它将提交RoleId值而不是Role Object，您需要定义public ICollection<int> UserRoleIds { get; set; }来接受RoleIds。

按照以下步骤操作：

1. 用UserRoleIds定义一个ViewModel

   public class UserVM
   {
       public UserVM()
       {
           IsActivo = true;
       }
   
       public int Id { get; set; }
   
       [Required]
       [Display(Prompt = "Username")]
       public string Username { get; set; }
       [Display(Name = "Último Acesso")]
       public DateTime? DataSessao { get; set; }
       [Display(Name = "Activo")]
       public bool IsActivo { get; set; }
   
       public ICollection<int> RoleIds { get; set; }
   }
   

2. 剃须刀型号

   public class CreateModel : PageModel
   {
       private readonly TestRazorContext _context;
   
       public CreateModel(TestRazorContext context)
       {
           _context = context;
       }
   
       public IActionResult OnGet()
       {
           RolesOptions = _context.Role.Select(d =>
                   new SelectListItem
                   {
                       Value = d.Id.ToString(),
                       Text = d.Type
                   }).ToList();
           return Page();
       }
   
       [BindProperty]
       public UserVM User { get; set; }
       public List<SelectListItem> RolesOptions { get; set; }
   
       public async Task<IActionResult> OnPostAsync()
       {
           if (!ModelState.IsValid)
           {
               return Page();
           }
           //create user
           var user = new User {
               Username = User.Username,
               //rest properties
           };
           _context.User.Add(user);
           await _context.SaveChangesAsync();
           //set user role
           var userRoles = new List<UserRoles>();
           foreach (var roleId in User.RoleIds)
           {
               userRoles.Add(new UserRoles
               {
                   UserId = user.Id,
                   RoleId = roleId
               });
           }
           _context.UserRole.AddRange(userRoles);
           await _context.SaveChangesAsync();
           return RedirectToPage("./Index");
       }
   }
   

3. 剃刀视图

   <form method="post">
       <div class="form-group">
           <label asp-for="User.Username" class="control-label"></label>
           <input asp-for="User.Username" />
       </div>    
       <div class="form-group">
           <label asp-for="User.RoleIds" class="control-label"></label>
           <select multiple="multiple" asp-for="User.RoleIds" asp-items="Model.RolesOptions" class="form-control form-control-sm">
               <option value="">Selecione um Departamento...</option>
           </select>
           <span asp-validation-for="User.RoleIds" class="text-danger"></span>
       </div>
       <input type="submit" value="Submit"/>
   </form>