Question

我创建了一个应用程序，员工输入他们的名字/姓氏，从下拉列表中选择他们的部门和约会。 CRUD操作一切正常。

但是，我需要从Appointments下拉列表中删除已分配给员工的值。每个约会只能有一名员工。因此，我需要在用户选择一个约会后从约会下拉列表中删除约会。

我使用的是ASP.NET Core 2.0，C＃，EntityFrameworkCore Code First和SQL Server 2016.

如果有人可以提供帮助，我现在附上我现有的代码。提前谢谢！

模型

public class Employee
{
    public int EmployeeID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public int DepartmentID { get; set; }
    public Department Department { get; set; }

    public int AppointmentID { get; set; }
    public Appointment Appointment { get; set; }
}

public class Department
{
    public int DepartmentID { get; set; }
    public string Name { get; set; }

    public ICollection<Employee> Employees { get; set; }
}

public class Appointment
{
    public int AppointmentID { get; set; }
    public string TimeSlot { get; set; }

    public ICollection<Employee> Employees { get; set; }
}

的ViewModels

public class EmployeeFormVM
{
    public int EmployeeID { get; set; }

    [Required(ErrorMessage = "Please enter your First Name")]
    [Display(Name = "First Name")]
    [StringLength(50)]
    public string FirstName { get; set; }

    [Required(ErrorMessage = "Please enter your Last Name")]
    [Display(Name = "Last Name")]
    [StringLength(50)]
    public string LastName { get; set; }

    [Required(ErrorMessage = "Please select your Department")]
    [Display(Name = "Department")]
    public int DepartmentID { get; set; }

    public IEnumerable<Department> Departments { get; set; }

    [Required(ErrorMessage = "Please select your Appointment")]
    [Display(Name = "Appointment")]
    public int AppointmentID { get; set; }

    public IEnumerable<Appointment> Appointments { get; set; }
}

的DbContext

public class WinTenDbContext : DbContext
{
    public WinTenDbContext(DbContextOptions<WinTenDbContext> options) : base(options)
    {
    }

    public DbSet<Employee> Employees { get; set; }
    public DbSet<Department> Departments { get; set; }
    public DbSet<Appointment> Appointments { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Employee>()
            .HasKey(e => e.EmployeeID);

        modelBuilder.Entity<Employee>()
            .Property(e => e.FirstName)
            .HasColumnType("varchar(50)")
            .HasMaxLength(50)
            .IsRequired();


        modelBuilder.Entity<Employee>()
            .Property(e => e.LastName)
            .HasColumnType("varchar(50)")
            .HasMaxLength(50)
            .IsRequired();            

        modelBuilder.Entity<Department>()
            .HasKey(d => d.DepartmentID);

        modelBuilder.Entity<Department>()
            .Property(d => d.Name)
            .HasColumnType("varchar(50)")
            .HasMaxLength(50);

        modelBuilder.Entity<Appointment>()
            .HasKey(a => a.AppointmentID);

        modelBuilder.Entity<Appointment>()
            .Property(a => a.TimeSlot)
            .HasColumnType("varchar(50)")
            .HasMaxLength(50);
    }
}

EmployeesController

public class EmployeesController : Controller
{
    private readonly WinTenDbContext _context;

    public EmployeesController(WinTenDbContext context)
    {
        _context = context;
    }

    // GET: Employees and their Departments
    public async Task<IActionResult> Index()
    {
        var webAppDbContext = _context.Employees.Include(d => d.Department).Include(a => a.Appointment);
        return View(await webAppDbContext.ToListAsync());
    }

    // GET: Employees/Details/5
    public async Task<IActionResult> Details(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        var employee = await _context.Employees
            .SingleOrDefaultAsync(m => m.EmployeeID == id);
        if (employee == null)
        {
            return NotFound();
        }

        return View(employee);
    }

    // GET: Employees/Create
    public IActionResult Create()
    {
        var departments = _context.Departments.ToList();
        var appointments = _context.Appointments.ToList();

        var viewModel = new EmployeeFormVM
        {
            Departments = departments,
            Appointments = appointments
        };

        return View(viewModel);
    }

    // POST: Employees/Create
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create(EmployeeFormVM employee)
    {
        if (ModelState.IsValid)
        {
            var emp = new Employee();
            {
                emp.FirstName = employee.FirstName;
                emp.LastName = employee.LastName;
                emp.DepartmentID = employee.DepartmentID;
                emp.AppointmentID = employee.AppointmentID;
            }

            // Query DB to check if Employee exists with same First/Last Name
            Employee existingEmployee = await _context.Employees.SingleOrDefaultAsync(m => m.FirstName == employee.FirstName && m.LastName == employee.LastName);
            if (existingEmployee != null)
            {
                // Display Error if duplicate employee
                ModelState.AddModelError(string.Empty, "An employee with this name has already registered");
                employee.Departments = _context.Departments.ToList();
                employee.Appointments = _context.Appointments.ToList();
                return View(employee);
            }

            // Query DB to check if appointment has already been assigned to an employee
            Employee existingAppointment = await _context.Employees.SingleOrDefaultAsync(m => m.AppointmentID == employee.AppointmentID);
            if (existingAppointment != null)
            {
                // Display error if the appointment was already chosen
                ModelState.AddModelError(string.Empty, "This appointment has already been taken. Please select another timeslot.");
                employee.Departments = _context.Departments.ToList();
                employee.Appointments = _context.Appointments.ToList();
                return View(employee);
            }

            _context.Add(emp);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }
        return View(employee);
    }

    // GET: Employees/Edit/5
    public async Task<IActionResult> Edit(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        var employeevm = new EmployeeFormVM();
        {
            Employee employee = await _context.Employees.SingleOrDefaultAsync(m => m.EmployeeID == id);

            if (employee == null)
            {
                return NotFound();
            }

            employeevm.EmployeeID = employee.EmployeeID;
            employeevm.FirstName = employee.FirstName;
            employeevm.LastName = employee.LastName;

            // Retrieve list of Departments
            var departments = _context.Departments.ToList();
            employeevm.Departments = departments;
            // Set the selected department
            employeevm.DepartmentID = employee.DepartmentID;

            // Retrieve list of Appointments
            var appointments = _context.Appointments.ToList();
            employeevm.Appointments = appointments;
            // Set the selected department
            employeevm.AppointmentID = employee.AppointmentID;
        }   
        return View(employeevm);
    }

    // POST: Employees/Edit/5
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Edit(EmployeeFormVM vmEdit)
    {
        if (ModelState.IsValid)
        {
            Employee employee = _context.Employees.SingleOrDefault(e => e.EmployeeID == vmEdit.EmployeeID);

            if (employee == null)
            {
                return NotFound();
            }

            employee.FirstName = vmEdit.FirstName;
            employee.LastName = vmEdit.LastName;
            employee.DepartmentID = vmEdit.DepartmentID;
            employee.AppointmentID = vmEdit.AppointmentID;

            try
            {
                _context.Update(employee);
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!EmployeeExists(vmEdit.EmployeeID))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }
            return RedirectToAction(nameof(Index));
        }
        return View(vmEdit);
    }

    // GET: Employees/Delete/5
    public async Task<IActionResult> Delete(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        var employee = await _context.Employees
            .SingleOrDefaultAsync(m => m.EmployeeID == id);
        if (employee == null)
        {
            return NotFound();
        }

        return View(employee);
    }

    // POST: Employees/Delete/5
    [HttpPost, ActionName("Delete")]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> DeleteConfirmed(int id)
    {
        var employee = await _context.Employees.SingleOrDefaultAsync(m => m.EmployeeID == id);
        _context.Employees.Remove(employee);
        await _context.SaveChangesAsync();
        return RedirectToAction(nameof(Index));
    }

    private bool EmployeeExists(int id)
    {
        return _context.Employees.Any(e => e.EmployeeID == id);
    }
}

创建视图

@using (Html.BeginForm("Create", "Employees"))
    {
        @Html.ValidationSummary(true, "", new { @class = "validation-summary-errors" })
        //@Html.ValidationSummary(true, "", new { @style = "color: #cc0000" })
        //@Html.ValidationSummary(true)

        <div class="form-group">
            @Html.LabelFor(e => e.FirstName)
            @Html.TextBoxFor(e => e.FirstName, new { @class = "form-control" })
            @Html.ValidationMessageFor(e => e.FirstName)
        </div>

        <div class="form-group">
            @Html.LabelFor(e => e.LastName)
            @Html.TextBoxFor(e => e.LastName, new { @class = "form-control" })
            @Html.ValidationMessageFor(e => e.LastName)
        </div>

        <div class="form-group">
            @Html.LabelFor(d => d.DepartmentID)
            @Html.DropDownListFor(d => d.DepartmentID, new SelectList(Model.Departments, "DepartmentID", "Name"), "", new { @class = "form-control" })
            @Html.ValidationMessageFor(d => d.DepartmentID)
        </div>

        <div class="form-group">
            @Html.LabelFor(a => a.AppointmentID)
            @Html.DropDownListFor(a => a.AppointmentID, new SelectList(Model.Appointments, "AppointmentID", "TimeSlot"), "", new { @class = "form-control" })
            @Html.ValidationMessageFor(a => a.AppointmentID)
        </div>

        <div class="form-group">
            <button type="submit" class="btn btn-primary">Submit</button>
        </div>
    }

修改视图

@using (Html.BeginForm("Edit", "Employees"))
    {
        <div class="form-group">
            @Html.LabelFor(e => e.FirstName)
            @Html.TextBoxFor(e => e.FirstName, new { @class = "form-control" })
            @Html.ValidationMessageFor(e => e.FirstName)
        </div>

        <div class="form-group">
            @Html.LabelFor(e => e.LastName)
            @Html.TextBoxFor(e => e.LastName, new { @class = "form-control" })
            @Html.ValidationMessageFor(e => e.LastName)
        </div>

        <div class="form-group">
            @Html.LabelFor(d => d.DepartmentID)
            @Html.DropDownListFor(d => d.DepartmentID, new SelectList(Model.Departments, "DepartmentID", "Name"), "", new { @class = "form-control" })
            @Html.ValidationMessageFor(d => d.DepartmentID)
        </div>

        <div class="form-group">
            @Html.LabelFor(a => a.AppointmentID)
            @Html.DropDownListFor(a => a.AppointmentID, new SelectList(Model.Appointments, "AppointmentID", "TimeSlot"), "", new { @class = "form-control" })
            @Html.ValidationMessageFor(a => a.AppointmentID)
        </div>

        @Html.HiddenFor(e => e.EmployeeID)

        <div class="form-group">
            <button type="submit" class="btn btn-primary">Submit</button>
        </div>
    }

Answer 1

您可以使用如下的简单LINQ查询：

var appointments = _context.Appointments.Include(x=>x.Employees).Where(x=>!x.Em‌ployees.Any()).ToLis‌t();

如果您需要重用代码，可以使用repository pattern并将此代码提取到另一个类。

每当您需要过滤数据时，例如在GET方法中，您将需要应用该查询对于POST方法，您可以跳过它，除非：

您想要验证。如果您怀疑用户可能已经篡改了输入，并以某种方式提供了无效的ID，那么您可能希望再次检查该过滤后的数据。
您想要管理并发 - 假设两个用户同时请求了该页面，并且可以使用特定的约会时段。如果两个的员工选择了相同的时段，该怎么办？在这种情况下，检查POST将有助于防止无效数据

ASP.NET Core 2.0检索/删除DropDownList值

1 个答案: