进入编辑视图前，需要获取此学生的ClassId，MajorId，GradeId以在进入视图后下拉列表能处于正确的选项。

添加GetWithClass方法

在StudentRepo中添加GetWithClass方法：

代码如下：

public Student? GetWithClass(Guid id)
{
    return DbSet.Include(s => s.Class).SingleOrDefault(s => s.Id == id);
}

这样获取的学生实体附带Class的数据。

添加GetEditModel方法

在StudentService中添加GetEditModel方法以获取学生实体及下拉列表数据。

代码如下：

public StudentViewModel GetEditModel(Guid id)
{
    Student? student = studentRepo.GetWithClass(id);
    if (student == null)
    {
        throw new NullReferenceException();
    }

    StudentViewModel model = new StudentViewModel()
    {
        Id = student.Id,
        Number = student.Number,
        Name = student.Name,
        Gender = student.Gender,
        Birthday = student.Birthday,
        ClassId = student.ClassId,
        MajorId = student.Class.MajorId,
        GradeId = student.Class.GradeId,

    };

    StudentViewModel selectListModel = GetSelectListModel();
    model.Majors = selectListModel.Majors;
    model.Grades = selectListModel.Grades;

    return model;
}

创建Edit动作

在StudentController中创建Edit动作，代码如下：

public IActionResult Edit(Guid id)
{
    StudentViewModel model;
    try
    {
        model = studentService.GetEditModel(id);
    }
    catch (NullReferenceException)
    {
        return NotFound();
    }
    return View(model);
}

创建Edit视图

创建Edit.cshtml，代码如下：

@{
    ViewBag.Title = "编辑学生";
}
@model StudentViewModel

<form method="post" class="mx-auto" style="width:320px;">
    <div asp-validation-summary="All" class="has-text-danger mb-4"></div>
    <input asp-for="Id" hidden>
    <div class="field">
        <label asp-for="MajorName" class="label"></label>
        <div class="control">
            <div class="select is-fullwidth">
                <select asp-for="MajorId" asp-items="Model.Majors"
                        hx-get="/Student/GetClassSelectPartial"
                        hx-target="#ClassId"
                        hx-include="#GradeId,#ClassId"
                        hx-swap="outerHTML">
                    <option value="">请选择</option>
                </select>
            </div>
        </div>
    </div>
    <div class="field">
        <label asp-for="GradeName" class="label"></label>
        <div class="control">
            <div class="select is-fullwidth">
                <select asp-for="GradeId" asp-items="Model.Grades"
                        hx-get="/Student/GetClassSelectPartial"
                        hx-target="#ClassId"
                        hx-include="#MajorId,#ClassId"
                        hx-swap="outerHTML">
                    <option value="">请选择</option>
                </select>
            </div>
        </div>
    </div>
    <div class="field">
        <label asp-for="ClassName" class="label"></label>
        <div class="control">
            <div class="select is-fullwidth">
                <input asp-for="ClassId" hx-get="/Student/GetClassSelectPartial"
                        hx-trigger="load"
                        hx-include="#MajorId,#GradeId"
                        hx-swap="outerHTML">
            </div>
        </div>
    </div>
    <div class="field">
        <label asp-for="Number" class="label"></label>
        <div class="control">
            <input asp-for="Number" class="input">
        </div>
    </div>
    <div class="field">
        <label asp-for="Name" class="label"></label>
        <div class="control">
            <input asp-for="Name" class="input">
        </div>
    </div>
    <div class="field">
        <label asp-for="Birthday" class="label"></label>
        <div class="control">
            <input asp-for="Birthday" class="input">
        </div>
    </div>
    <div class="field">
        <label asp-for="Gender" class="label"></label>
        <div class="control">
            <label class="radio">
                <input type="radio" asp-for="Gender" value="false">
                男
            </label>
            <label class="radio">
                <input type="radio" asp-for="Gender" value="true" >
                女
            </label>
        </div>
    </div>
    <div class="field">
        <button class="button is-primary is-fullwidth">提交</button>
    </div>
</form>

添加Update方法

在StudentService中添加Update方法，代码如下：

public void Update(StudentViewModel model)
{
    Student student = new()
    {
        Id = model.Id,
        ClassId = model.ClassId,
        Number = model.Number,
        Name = model.Name,
        Gender = model.Gender,
        Birthday = model.Birthday,
    };
    studentRepo.Update(student);
}

创建post请求的Edit动作

和Add动作类似，只不过调用了Update方法，代码如下：

[HttpPost]
public IActionResult Edit(StudentViewModel model)
{
    if (ModelState.IsValid)
    {
        try
        {
            studentService.Update(model);
            return RedirectToAction("Index");
        }
        catch (DbUpdateException)
        {
            ModelState.AddModelError(nameof(Student.Number), "学号不能重复");
        }
    }
    if (model.ClassId == Guid.Empty)
    {
        ModelState.Remove(nameof(Student.ClassId));
        ModelState.AddModelError(nameof(Student.ClassId), "请选择班级");
    }
    StudentViewModel studentViewModel = studentService.GetSelectListModel();
    model.Majors = studentViewModel.Majors;
    model.Grades = studentViewModel.Grades;
    return View(model);
}