如何检查用户名是否已经被占用

本文关键字：是否 用户 何检查 检查 | 更新日期: 2023-09-27 18:09:57

我使用数据库优先，并通过ViewModel验证我的输入。但是，我想检查是否已经在db中采取了UserName。我怎么做呢?这是我设法得到的程度(我可以验证和保存):

[Required]
[StringLength(50)]
[MinLength(3, ErrorMessage = "You must at least have 3 letters")]
public string UserName { get; set; }

和以下是我的寄存器代码在控制器:

    [HttpGet]
    public ActionResult Register() {
        return View();
    }
    [HttpPost]
    public ActionResult Register(UserVIewModel reg) {
        if (ModelState.IsValid)
        {
            var m = new User {
                UserName = reg.UserName,
                Email = reg.Email,
                FirstName = reg.FirstName,
                LastName = reg.LastName,
                Password = reg.Password
            };
            db.Users.Add(m);
            db.SaveChanges();
            return RedirectToAction("Login");
        }
        return View();
    }

如何检查用户名是否已经被占用

这就是如何在Register()方法中检查用户

[HttpPost]
public ActionResult Register(UserVIewModel reg) {
    if (ModelState.IsValid)
    {
        if (db.Users.Where(u => u.UserName == reg.UserName).Any())
        {
           //Do what do u need to do...
        }
        else
        {
          var m = new User {
            UserName = reg.UserName,
            Email = reg.Email,
            FirstName = reg.FirstName,
            LastName = reg.LastName,
            Password = reg.Password
          };
          db.Users.Add(m);
          db.SaveChanges();
          return RedirectToAction("Login");
        }
    }
    return View();
}

这将查询并返回数据库中匹配条件或为空的第一个条目db.Users.FirstOrDefault(x => x.UserName == reg.UserName)

所以我只是检查查询是否返回值或null并设置bool(见下面的代码)

注意x，您可以使用其他字母或单词。可能是data => data.UserName....或row => row.UserName...或result => result.UserName...，它只是代表db的模型

类似这样的内容(也将代码重新排列了一下)

[HttpPost]
public ActionResult Register(UserVIewModel reg) {
    if (!ModelState.IsValid)
    {
         return View(model);
    }
    // here is the main answer to your question
    bool userExists = db.Users.FirstOrDefault(x => x.UserName == reg.UserName) != null;
    // and then use the bool to see if you need to return an error
    if (userExists) { 
        // I'm not 100% sure about this part so double-check this
        // but I think it's pretty close to this
        ModelState.AddModelError("UserName","UserName taken");
        return View(model);
    }

    // If the userExists = false then code continues here
    var m = new User {
        UserName = reg.UserName,
        Email = reg.Email,
        FirstName = reg.FirstName,
        LastName = reg.LastName,
        Password = reg.Password
    };
    db.Users.Add(m);
    db.SaveChanges();
    return RedirectToAction("Login");
}
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