在多对多关联表上执行标准SQL语句，以在编辑方法中删除多对多关联条目。可以通过使用DbContext来执行SQL语句。

以下是示例代码：

public async Task Edit(int id, StudentViewModel model)
{
    if (ModelState.IsValid)
    {
        var student = await _context.Students
            .Include(s => s.StudentCourses)
            .SingleOrDefaultAsync(s => s.Id == id);

        if (student != null)
        {
            //delete all existing student courses
            var deleteSql = $"DELETE FROM StudentCourses WHERE StudentId = '{id}'";
            await _context.Database.ExecuteSqlCommandAsync(deleteSql);

            //update student properties
            student.Name = model.Name;
            student.Age = model.Age;

            //add newly selected student courses
            foreach (var courseId in model.SelectedCourseIds)
            {
                var studentCourse = new StudentCourse
                {
                    StudentId = id,
                    CourseId = courseId
                };

                _context.Add(studentCourse);
            }

            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }
    }

    return View(model);
}