在仅更新除图像以外的其他字段时，具有怪异的功能，其他字段（FirstName，LastName）成功更新，但是Image将其自身设置为null，但是当我根据其他字段（FirstName，LastName）选择它，它会成功更新。所以我想要的是当我不更新图像时将其保持原样，而无需将其自身设置为null。
这是我的New.cshtm文件，它同时处理创建和编辑数据：
<form asp-action="New" method="Post" asp-controller="Student" enctype="multipart/form-data">
<div asp-validation-summary="All"></div>
<input asp-for="Id" type="hidden"/>
<input name="IsEditMode" id="IsEditMode" value="@ViewBag.IsEditMode" type="hidden"/>
<div class="form-row">
<label>Upload Photo</label>
<input asp-for="ImageUrl" type="file" id="file" name="file" class="form-control"/>
</div>
<div class="form-row">
<div class="col">
<label asp-for="FirstName"></label>
<input asp-for="FirstName" class="form-control"/>
<span asp-validation-for="FirstName" class="text-danger"></span>
</div>
<div class="col">
<label asp-for="MiddleName"></label>
<input asp-for="MiddleName" class="form-control"/>
<span asp-validation-for="MiddleName" class="text-danger"></span>
</div>
</div>
</form>
然后这些是我的 controller Student.cs正在用来更新字段的方法：
public IActionResult New(Student student, string IsEditMode, IFormFile file)
{
if (!ModelState.IsValid)
{
ViewBag.IsEditMode = IsEditMode;
return View(student);
}
try
{
if (IsEditMode.Equals("false"))
{
_studentRepository.Create(student);
UploadFile(file, student.Id);
_toastNotification.AddSuccessToastMessage("Student has been created successfully.");
}
else
{
_studentRepository.Edit(student);
UploadFile(file, student.Id);
_toastNotification.AddSuccessToastMessage("Student has been edited successfully.");
}
return RedirectToAction(nameof(Index));
}
catch (Exception e)
{
return RedirectToAction(nameof(Index));
}
}
public IActionResult Edit(int id)
{
try
{
ViewBag.IsEditMode = "true";
var student = _studentRepository.GetSingleStudent(id);
return View("New", student);
}
catch (Exception ex)
{
return Content("Could not find Pet");
}
}
public void UploadFile(IFormFile file, long studentId)
{
var fileName = file.FileName;
var path = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot/images",fileName);
using (var fileStream = new FileStream(path, FileMode.Create))
{
file.CopyTo(fileStream);
}
var student = _studentRepository.GetSingleStudent(studentId);
student.ImageUrl = fileName;
_studentRepository.Edit(student);
}
然后，这就是我在存储库中更新的方式：
然后在我的存储库中，这就是我更新字段“：
public void Edit(Student student)
{
var existingStudent = _context.Students
.FirstOrDefault(s => s.Id == student.Id);
if (existingStudent != null)
{
// updating student.
_context.Entry(existingStudent).CurrentValues.SetValues(student);
_context.Entry(existingStudent).State = EntityState.Modified;
}
}
Index.cshtml，这是一个图像列表，其中包括名字和姓氏以及（动作按钮） Edit，Delete按钮：
<table class="table table-striped">
<thead class="thead-dark">
<tr>
<td ><b>Student Picture</b></td>
<td><b>FirstName</b></td>
<td><b>LastName</b></td>
<td colspan="2"> <b>Actions</b></td>
</tr>
</thead>
<tbody>
@foreach (var student in Model)
{
<tr>
<td>@student.StudentRegNo</td>
<td>
<div class="thumbnail">
<img src="/images/@student.ImageUrl" width="90" height="90"/>
</div>
</td>
<td>@student.FirstName</td>
<td>@student.LastName</td>
<d>
<td>
<a class="btn btn-warning" asp-action="Details" asp-controller="Student" asp-route-Id="@student.Id">Details</a>
</td>
<td>
<a class="btn btn-primary" asp-action="edit" asp-route-Id="@student.Id">Edit</a>
</td>
<td>
<a
class="btn btn-danger delete"
asp-route-Id="@student.Id"
asp-action="Delete">
Delete
</a>
</td>
</d>
</tr>
}
</tbody>
</table>
这是根据@Raul解决方案的当前逻辑，但它不起作用：
if (student.ImageUrl != null)
{
_context.Entry(existingStudent).CurrentValues.SetValues(student);
_context.Entry(existingStudent).State = EntityState.Modified;
}
else
{
_context.Entry(existingStudent).Property(x => x.ImageUrl).IsModified = false;
_context.Entry(existingStudent).CurrentValues.SetValues(student);
_context.Entry(existingStudent).State = EntityState.Modified;
}
答案 0 :(得分：1)
在您的Edit学生方法中，可以将ImageUrl IsModified的{{1}}设置为false，这不会更新数据库中的image字段：
Property当然，您需要在此检查您的public void Edit(Student student)
{
var existingStudent = _context.Students.FirstOrDefault(s => s.Id == student.Id);
if (existingStudent != null)
{
// updating student.
_context.Student.Attach(existingStudent);
_context.Entry(existingStudent).State = EntityState.Modified;
_context.Entry(existingStudent).Property(x => x.ImageUrl).IsModified=false;
_context.SaveChanges();
}
}
逻辑。如果获得新图像，则将相应地更新模型。
编辑：
您可以像这样合并if-else条件：
ImageUrl答案 1 :(得分：1)
您可以分别考虑这两种情况。在不更新图像而更新字段时，文件为null，则需要将现有学生的ImageUrl关联到发布的学生。
//...
try
{
if (IsEditMode.Equals("false"))
{
_studentRepository.Create(student);
UploadFile(file, student.Id);
_toastNotification.AddSuccessToastMessage("Student has been created successfully.");
}
else
{
//edit mode
if(file == null)//Updating fields without updating the image.
{
var existingStudent = _context.Students.FirstOrDefault(s => s.Id == student.Id);
if (existingStudent != null)
{
// updating student with previousImageUrl
student.ImageUrl = existingStudent.ImageUrl;
_context.Entry(existingStudent).CurrentValues.SetValues(student);
_context.Entry(existingStudent).State = EntityState.Modified;
_context.SaveChanges();
}
}
else//Updating the fields and the image
{
_studentRepository.Edit(student);
UploadFile(file, student.Id);
}
_toastNotification.AddSuccessToastMessage("Student has been edited successfully.");
}
return RedirectToAction(nameof(Index));
}
catch (Exception e)
{
return RedirectToAction(nameof(Index));
}
}
public void UploadFile(IFormFile file, long studentId)
{
var fileName = file.FileName;
var path = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot/images", fileName);
using (var fileStream = new FileStream(path, FileMode.Create))
{
file.CopyTo(fileStream);
}
var student = _studentRepository.GetSingleStudent(studentId);
student.ImageUrl = fileName;
_studentRepository.Edit(student);
}
public void Edit(Student student)
{
var existingStudent = _context.Students
.FirstOrDefault(s => s.Id == student.Id);
if (existingStudent != null)
{
// updating student.
_context.Entry(existingStudent).CurrentValues.SetValues(student);
_context.Entry(existingStudent).State = EntityState.Modified;
_context.SaveChanges();
}
}