我最近开始使用ASP.NET，必须说我非常喜欢它。但是在每种关系中，您都必须在这里和那里遇到一些障碍。这是我的：
我的起始项目包括创建用于管理学生的简单学校系统。我有几个表（学生，学生地址，年级和课程）。
这是有问题的两个表：
1）学生桌：
public Student()
{
this.Courses = new HashSet<Course>();
}
public int StudentId { get; set; }
[Required]
[StringLength(50, MinimumLength = 2, ErrorMessage = "The name must have over 2 and under 50 characters!")] // stavlja ograničenje na duljinu stringa u bazi
public string Name { get; set; }
[Required]
[StringLength(50, MinimumLength = 2, ErrorMessage = "The name must have over 2 and under 50 characters!")]
public string Surname { get; set; }
public int CurrentGradeId { get; set; }
public Grade CurrentGrade { get; set; }
public virtual StudentAdress Address { get; set; }
public virtual ICollection<Course> Courses { get; set; }
2）StudentAddress表：
public int StudentId { get; set; }
public string Address1 { get; set; }
public string Adress2 { get; set; }
public string City { get; set; }
public int ZipCode { get; set; }
public string Country { get; set; }
public virtual Student Student { get; set; }
简而言之，当我在“学生”编辑“操作方法”时，我正在尝试更新StudentAddresses属性（更精确地说是Student的Address1属性）。
这是“编辑视图”学生：
@using (Html.BeginForm())
{
@Html.AntiForgeryToken()
<div class="form-horizontal">
<h4>Student</h4>
<hr />
@Html.ValidationSummary(true, "", new { @class = "text-danger" })
@Html.HiddenFor(model => model.StudentId)
<div class="form-group">
@Html.LabelFor(model => model.Name, htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.EditorFor(model => model.Name, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.Name, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
@Html.LabelFor(model => model.Surname, htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.EditorFor(model => model.Surname, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.Surname, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
@Html.LabelFor(model => model.CurrentGradeId, "CurrentGradeId", htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.DropDownList("CurrentGradeId", null, htmlAttributes: new { @class = "form-control" })
@Html.ValidationMessageFor(model => model.CurrentGradeId, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
@Html.LabelFor(model => model.Address.Address1, htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.EditorFor(model => model.Address.Address1, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.Address.Address1, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="Save" class="btn btn-default" />
</div>
</div>
</div>
最后是“ StudentsController”的“编辑操作方法”：
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit([Bind(Include = "StudentId,Name,Surname,CurrentGradeId")] Student student )
{
if (ModelState.IsValid)
{
// getting student id for current studentid
StudentAdress addresa = db.Addresses.Find(student.StudentId);
// trying to bind input value
addresa.Address1 = student.Address.Address1.ToString();
// saving new value in StudentAddresses field Address1
db.Entry(addresa).State = EntityState.Modified;
db.SaveChanges();
db.Entry(student).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
ViewBag.CurrentGradeId = new SelectList(db.Grades, "GradeId", "GradeName", student.CurrentGradeId);
return View(student);
}
因此，在Edit方法中，我想在Student表的Edit方法中保存Address1的新输入值。或更简单地说，我想在编辑Student类时更新StudentAddress类中的Address1字段
更新1
因此，可以说我已经弄清楚了，但是我仍然想知道这样做是否正确和正确。
在“学生编辑”操作方法中，我添加了
addresa.Address1 = Request.Form["Address.Address1"];，其中我使用属性name=Address.Address1更新了字段，这起到了技巧，但我想知道这样做是否正确？请记住，我已经尝试过
**addresa.Address1 = student.Address.Address1;**
但是使用这种“更清洁”的方法给了我：
System.NullReferenceException：对象引用未设置为实例
一个对象。
我可以使用其他方法更新Address.Address1字段吗？
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit([Bind(Include = "StudentId,Name,Surname,CurrentGradeId")] Student student )
{
if (ModelState.IsValid)
{
StudentAdress addresa = db.Addresses.Find(student.StudentId);
// newly added line
addresa.Address1 = Request.Form["Address.Address1"];
db.Entry(addresa).State = EntityState.Modified;
db.SaveChanges();
db.Entry(student).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
ViewBag.CurrentGradeId = new SelectList(db.Grades, "GradeId", "GradeName", student.CurrentGradeId);
return View(student);
}
最佳答案
你的关系错了。
在您的StudentAddress模型中，我们可以看到StudentId外键，这意味着Student和StudentAddress之间的关系是一对多的。但是在您的Student模型中，您有virtual StudentAdress Address应该是ICollection<StudentAdress> Addresses。
在添加/编辑中，您可以执行以下操作：
var student = context.Student.Find(1);
student.Addresses.Add(new StudentAdress {
Address1 = "Ul. Janka Leskovara",
City = "Pregrada",
ZipCode = 49218,
Country = "Hrvatska"
});
context.SaveChanges();
关于c# - 如何从ASP.NET MVC中的相关表更新表属性，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/48355226/