使用 Entity Framework 6 和 ViewModel 从数据库 table 在 ASP.NET MVC 中填充 DropDownList

Question

为了一个可以使用 ajax/jquery 和存储过程快速解决的问题，我绞尽脑汁整整一夜。我要

1) 使用 Entity Framework 和视图模型从数据库 table 获得的值填充下拉列表。我不想使用 VIEWBAG 或 VIEWDATA。任何帮助表示赞赏。

2) 如何使用具有所有默认字段的视图模型生成创建视图？脚手架适用于模型但不适用于视图模型？

我的模型

public class Employee
{
    public int EmployeeID { get; set; }
    public string Name { get; set; }
    public string Gender { get; set; }
    public string City { get; set; }
    public string Level { get; set; }
    public int DepartmentId { get; set; }
}

public class Grade
{
    public int ID { get; set; }
    public string Level { get; set; }
}

查看模型

public class GradeSelectListViewModel
{

    public Employee Employee { get; set; }
    public IEnumerable<SelectListItem> Grades { get; set; }
    public GradeSelectListViewModel(Employee employee, IEnumerable grades)
    {
        Employee = employee;
        Grades = new SelectList(grades, "Grade", "Name", employee.Level);
    }
}

我的背景CLASS

public class EmployeeContext : DbContext
{
    public DbSet<Employee> Employees { get; set; }
    public DbSet<Department> Departments { get; set; }
    public DbSet<Grade> Grades { get; set; }
}

我的控制器

public ActionResult Edit (int? id)
{
    using (var db = new EmployeeContext())
    {
        var model = new GradeSelectListViewModel(db.Employees.Find(id), db.Grades);
        //model.Employee = db.Employees.Single(x => x.EmployeeID == id);
        model.Grades = db.Grades.ToList().Select(x => new SelectListItem
        {
            Value = x.ID.ToString(),
            Text = x.Level
        });
        return View(model);
    }
}

我的 RAZOR 页面 CSHTML

@model MVCDemo.ViewModels.GradeSelectListViewModel
....
@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()
    ....
    @Html.DropDownListFor(x => Model.Employee.Level,
        new SelectList(Model.Grades, "ID", "Level"),
        "Select Level")
    ....
    <input type="submit" value="Create" class="btn btn-default" />
}

Answer 1

主要问题是在视图中您有 new SelectList(Model.Grades, "ID", "Level") 但 Grades 是 IEnumerable<SelectListItem> 并且 SelectListItem 不包含名为 ID 和 Level.

但是您的代码还有一些其他问题。首先，视图模型不应包含数据模型，而您的视图模型应该是

public class GradeSelectListViewModel
{
    public int? ID { get; set; } // make this ID so you do not need an input for it
    public string Name { get; set; }
    .... // other properties of Employee that your editing
    [Required(ErrorMessage = "..")]
    public int? Level { get; set; } // make value types nullable to protect against under-posting attacks
    public IEnumerable<SelectListItem> Grades { get; set; }
}

并根据需要添加显示和验证属性。注意我删掉了构造函数（你好像没有用，但是如果你用了，那么你还需要包含一个无参数的构造函数，否则提交到POST方法时会抛出异常. 我还假设 Level 应该是 typeof int 因为你绑定到 Grade.

的 int ID 属性

GET 方法中的代码应该是

Employee employee = db.Employees.Find(id);
var model = new GradeSelectListViewModel()
{
    ID = employee.EmployeeID,
    Name = employee.Name,
    Level = employee.Level, // convert to int?
    ....
    Grades = db.Grades.Select(x => new SelectListItem
    {
        Value = x.ID.ToString(),
        Text = x.Level
    })
};
return View(model);

并在视图中

 @Html.DropDownListFor(x => Model.Level, Model.Grades, "Select Level")

另请注意，在 POST 方法中，如果 return 视图因为 ModelState 无效，则需要重新分配 SelectList。

Answer 2

您可以使用以下方法在同一视图中填充三个 DropDownListFor：

ViewModel:

public class GroupViewModel
{  
    public IEnumerable<SelectListItem> Schedules { get; set; }
    public int ScheduleId { get; set; }

    public IEnumerable<SelectListItem> Labs { get; set; }
    public int LabId { get; set; }

    public IEnumerable<SelectListItem> Terms { get; set; } 
    public int TermId { get; set; }
}

控制器：

public ActionResult Create()
{
    //Populate DropDownList binding values
    var model = new GroupViewModel
    {
        //Preselect the Lab with id 2
        //LabId = 2,

        Labs = repository.Labs.Select(c => new SelectListItem
        {
            Value = c.Id.ToString(),
            Text = c.Name
        }),
        Terms = repository.Terms.Select(c => new SelectListItem
        {
            Value = c.Id.ToString(),
            Text = c.Name
        }),
        Schedules = repository.Schedules.Select(c => new SelectListItem
        {
            Value = c.Id.ToString(),
            Text = c.Name
        })
    };
    return View("Create", model);
}

查看：

@Html.DropDownListFor(m => m.LabId, new SelectList(Model.Labs, "Value", "Text"), 
    "Select", new { @class = "selectpicker" })

@Html.DropDownListFor(m => m.ScheduleId, new SelectList(Model.Schedules, "Value", "Text"), 
    "Select", new { @class = "selectpicker" })

@Html.DropDownListFor(m => m.TermId, new SelectList(Model.Terms, "Value", "Text"), 
    "Select", new { @class = "selectpicker" })

希望这对您有所帮助...

使用 Entity Framework 6 和 ViewModel 从数据库 table 在 ASP.NET MVC 中填充 DropDownList

Populate DropDownList in ASP.NET MVC from database table using Entity Framework 6 and ViewModel

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