没有保存在数据库中也没有错误，多对多关系

Question

用户与 post 之间存在多对多关系。我想在 post table 和具有 postID 的关联 table 中创建新值并登录用户 ID。没有错误消息，看起来我可以在运行应用程序时创建一个 post，但任何 table 中都没有保存任何内容。当我运行调试时，我可以看到它完成了所有步骤，甚至保存到数据库中。怎么了？

Post 型号

public class Post
    {
        public Post()
        {
            this.ApplicationUser = new HashSet<ApplicationUser>();
        }

        public int PostId { get; set; }
        public string Message { get; set; }
        public DateTime MessageDate { get; set; }

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

IdentityModels

 public class ApplicationUser : IdentityUser
    {
       public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
        {
            // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
            var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
            // Add custom user claims here
            return userIdentity;
        }

       public ApplicationUser()
       {
           this.Posts = new HashSet<Post>();
       }

       public virtual ICollection<Post> Posts { get; set; }
    }

我的创建函数创建了一个新的post

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "PostId,Message,MessageDate")] Post post)
    {
        var manager = Request.GetOwinContext().GetUserManager<ApplicationUserManager>();
        var userId = User.Identity.GetUserId();
        var user = manager.FindById(userId);

        if (ModelState.IsValid)
        {
            user.Posts.Add(post);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        return View(post);
    }

我在用户（经理、用户 ID、用户）和三个 tables（Posts、AspNetUsers 和 ApplicationUserPost）的所有变量中都有值

更新

我尝试附加时出错（以及来自 CodeNotFound 的解决方案）。

Error 1 'System.Data.Entity.IDbSet' does not contain a definition for 'FindById' and no extension method 'FindById' accepting a first argument of type 'System.Data.Entity.IDbSet' could be found (are you missing a using directive or an assembly reference?)

Error 2 'FreePost.Models.ApplicationDbContext' does not contain a definition for 'Attach' and no extension method 'Attach' accepting a first argument of type 'FreePost.Models.ApplicationDbContext' could be found (are you missing a using directive or an assembly reference?)

第一个错误消息是我选择使用 userManager 的原因。

Answer 1

它不起作用，因为您的 db.SaveChanges 什么都不做。您的上下文什么都不做，因为它对您尝试添加的 Post 实例一无所知。

要解决此问题，您需要首先将 ApplicationUser 的当前实例附加到如下上下文：

var manager = Request.GetOwinContext().GetUserManager<ApplicationUserManager>();
var userId = User.Identity.GetUserId();
var user = manager.FindById(userId);

if (ModelState.IsValid)
{
    // Line below you tell your DbContext to take care of ApplicationUser instance. 
    db.Users.Attach(user); 
    user.Posts.Add(post);
    db.SaveChanges();
    return RedirectToAction("Index");
}

旁注：我将像这样重构您的代码：

if (ModelState.IsValid)
{
    // Move your code that query the database here so you query your database only if the model is valid.
    var userId = User.Identity.GetUserId();

    // You don't need ApplicationUserManager instance to get the ApplicationUser  instance. 
    // If your Post class have a UserId foreign key property then this line is uselesss.
    // Just set the UserId property of Post class.
    var user = db.Users.Find(userId);
    user.Posts.Add(post);
    db.SaveChanges();
    return RedirectToAction("Index");
}

没有保存在数据库中也没有错误，多对多关系

Nothing saved in database and no errors, many to many relation

asp.net-mvc

many-to-many

entity-framework

code-first

asp.net-mvc-4