ASP.NET Core 2.0 防止重复条目答案

【问题标题】：ASP.NET Core 2.0 Prevent Duplicate EntriesASP.NET Core 2.0 防止重复条目
【发布时间】：2017-09-26 19:53:50
【问题描述】：

我对 ASP.NET Core MVC 非常陌生。我正在使用 ASP.NET Core 2.0、C#、EntityFrameworkCore Code First 和 SQL Server 2016。我设法让我的 CRUD 操作根据需要工作。

但是，我需要帮助来防止用户在我的表单上进行多次注册。如果可能的话，我想在控制器端的代码中检查/防止重复条目，而不是在数据库中。

如果有人可以提供帮助，我将附上我现在拥有的代码。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; }
}

视图模型

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; }
}

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
    public async Task<IActionResult> Index()
    {
        //return View(await _context.Employees.ToListAsync());

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

        else
        {
            employee.Departments = _context.Departments.ToList();
            employee.Appointments = _context.Appointments.ToList();
            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"))
    {
        <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>
    }

【问题讨论】：

标签： c# asp.net-core asp.net-core-mvc asp.net-core-2.0

【解决方案1】：

您当然可以从代码端检查重复条目，但您当然需要对数据库运行查询才能实现此目的。从您发布的代码中，您已经在EmployeesController.Edit 中做了类似的事情：

Employee employee = await _context.Employees.SingleOrDefaultAsync(
    m => m.EmployeeID == id);

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

您可以采用这种方法并将变体应用于EmployeesController.Create。例如：

Employee existingEmployee = await _context.Employees.SingleOrDefaultAsync(
    m => m.FirstName == employee.FirstName && m.LastName == employee.LastName);

if (existingEmployee != null)
{
    // The employee already exists.
    // Do whatever you need to do - This is just an example.
    ModelState.AddModelError(string.Empty, "This employee already exists.");
    employee.Departments = _context.Departments.ToList();
    employee.Appointments = _context.Appointments.ToList();
    return View(employee);
}

// Your existing code for creating a new employee.

我在SingleOrDefaultAsync 中使用的表达式只是一个示例：您需要根据自己的要求决定是什么让员工与众不同。

要查看我显示的控制器代码中添加的错误消息，您需要更新创建视图：

@using (Html.BeginForm("Create", "Employees"))
{
    @Html.ValidationSummary(true)
    ...

【讨论】：

感谢您的回复。我是否应该在我的原始发布代码中实现您提供的内容？我尝试将您提供的内容放入 [HttpPost]Create if(ModelState.IsValid) 代码中，但是当我尝试输入重复的名字和姓氏时，我收到此错误 ArgumentNullException: Value不能为空。参数名称：items 这行代码 @Html.DropDownListFor(d => d.DepartmentID, new SelectList(Model.Departments, "DepartmentID", "Name"), "", new { @ class= "表单控制" })
我已编辑答案以解决您的具体问题。您需要考虑对函数进行一些重组以删除此添加的重复项，但我认为这超出了您在此处的具体问题的范围。
谢谢你，成功了。但是，我没有看到错误消息 此员工已存在。 当我尝试输入重复条目时，我必须在创建视图中添加什么吗？另外，我是否有理由必须重组您提到的功能。
答案已更新。您不需要需要重新构造函数 - 这只是一个建议，考虑到您有重复填充 Departments 和 Appointments 列表的代码这一事实。
我建议您使用 .FirstOrDefaultAsync 而不是 SingleOrDefaultAsync，特别是如果数据库已经有数据并且可能已经存在重复。在这种情况下， SingleOrDefaultAsync 会抛出错误，但 FirstOrDefaultAsync 会按预期工作。如果是干净的项目，那么 SingleOrDefaultAsync 应该没问题，但还是 Single 更安全。