使用.SaveChanges()；保存电子邮件时出错

当我将电子邮件留空并提交注册表单时，它会将表单输入正确保存到数据库中。但是，当我包含一封电子邮件(例如：testemail@gmail.com)当db。SaveChanges((；被调用。

我收到的错误是：

EntityFramework.dll中发生类型为"System.Data.Entity.Validation.DbEntityValidationException"的异常，但未在用户代码中处理

附加信息：一个或多个实体的验证失败。有关详细信息，请参阅"EntityValidationErrors"属性。

控制器：

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Net;
using System.Web;
using System.Web.Mvc;
using Mkq.Models;
namespace Mkq.Controllers
{
    public class TeacherController : Controller
    {
        private MkqDbEntities db = new MkqDbEntities();
    [HttpPost]
    [AllowAnonymous]
    [ValidateAntiForgeryToken]
    public ActionResult Register([Bind(Include="teacher_id,subscription_id,teacher_fname,teacher_lname,username,password,email,teacher_credNumber,teacher_credST")] Teacher teacher)
    {
        teacher.subscription_id = 1;
        teacher.teacher_credNumber = null;
        teacher.teacher_credST = null;
        if (ModelState.IsValid)
        {
            db.Teachers.Add(teacher);
            db.SaveChanges();     //Error occurs when submitted
            return View();
        }
        // If we got this far, something failed, redisplay form
        return View(teacher);
    }

型号：

namespace Mkq.Models
{
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
public partial class Teacher
{
    public Teacher()
    {
        this.Quiz_info = new HashSet<Quiz_info>();
        this.Students = new HashSet<Student>();
    }
    [DisplayName("Teacher ID")]
    public int teacher_id { get; set; }
    [DisplayName("Subscription ID")]
    public int subscription_id { get; set; }
    [DisplayName("First Name")]
    public string teacher_fname { get; set; }
    [DisplayName("Last Name")]
    public string teacher_lname { get; set; }
    [DisplayName("Username")]
    public string username { get; set; }
    [DisplayName("Password")]
    public string password { get; set; }
    [RegularExpression("^[a-zA-Z0-9_''.-]+@([a-zA-Z0-9-]+''.)+[a-zA-Z]{2,6}$", ErrorMessage = "E-mail is not valid")]
    [DisplayName("Email")]
    public string email { get; set; }
    [DisplayName("Credential Number")]
    public string teacher_credNumber { get; set; }
    [DisplayName("Credential")]
    public string teacher_credST { get; set; }
    public virtual ICollection<Quiz_info> Quiz_info { get; set; }
    public virtual ICollection<Student> Students { get; set; }
    public virtual Subscription Subscription { get; set; }
}
}

视图：

@model Mkq.Models.Teacher
@{
    ViewBag.Title = "Teacher Registration";
}
<h2>@ViewBag.Title.</h2>
@using (Html.BeginForm("Register", "Account", FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
    @Html.AntiForgeryToken()
    <h4>Create a new account.</h4>
    <hr />
    @Html.ValidationSummary()
    <div class="form-group">
        @Html.LabelFor(m => m.teacher_fname, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.TextBoxFor(m => m.teacher_fname, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.teacher_lname, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.TextBoxFor(m => m.teacher_lname, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.username, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
           @Html.TextBoxFor(m => m.username, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.password, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.PasswordFor(m => m.password, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.email, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.TextBoxFor(m => m.email, new { @class = "form-control" })
            @Html.ValidationMessageFor(m => m.email)
        </div>
    </div>
    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" class="btn btn-default" value="Register" />
        </div>
    </div>
}
@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

catch (System.Data.Entity.Validation.DbEntityValidationException ex)
{
   foreach (var e in ex.EntityValidationErrors)
   {
      //check the ErrorMessage property
   }
}

try
{
  db.SaveChanges();
}
catch (DbEntityValidationException ex)
            {
                foreach (var entityValidationErrors in ex.EntityValidationErrors)
                {
                    foreach (var validationError in entityValidationErrors.ValidationErrors)
                    {
                        Response.Write("Property: " + validationError.PropertyName + " Error: " + validationError.ErrorMessage);
                    }
                }
            }