使用Entity Framework 6和ViewModel从数据库表填充ASP.NET MVC中的DropDownList [英] Populate DropDownList in ASP.NET MVC from database table using Entity Framework 6 and ViewModel

问题描述

我整夜都在努力解决一个问题，我可以使用ajax/jquery和存储过程来快速完成此问题.我想

I have been scratching my head for a whole night on an issue I can do quickly using ajax/jquery and stored procedures. I want to

1)使用实体框架和视图模型，从从数据库表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.

1) Populate a drop down list from values obtained from a database table using Entity Framework and view model. I DO NOT WANT TO USE VIEWBAG OR VIEWDATA. Any help appreciated.

2)如何使用带有所有默认字段的视图模型生成创建视图?脚手架只能在模型上工作，而不能在视图模型上工作?

2) How can I generate a Create View using the View Model with the all the default fields ? The scaffholding works on a model but not on a view model ?

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);
    }
}

我的语境课

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 PAGE CSHTML

MY RAZOR PAGE 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" />
}

推荐答案

主要问题是，在视图中您具有new SelectList(Model.Grades, "ID", "Level")，但Grades是IEnumerable<SelectListItem>，并且SelectListItem不包含名为ID的属性和Level.

The main issue is that in the view you have new SelectList(Model.Grades, "ID", "Level") but Grades is IEnumerable<SelectListItem> and SelectListItem does not contain properties named ID and Level.

但是您的代码还有其他一些问题.首先，视图模型不应包含数据模型，而您的视图模型应为

However there are a a few other issues with your code. First a view model should not contain a data model, and instead your view model should be

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.请注意，我删除了构造函数(您似乎并没有使用它，但是如果您这样做了，那么您还需要包含一个无参数的构造函数，否则在提交给POST方法时将引发异常.我也假设由于您绑定到Grade的int ID属性，因此Level应该为type int.

and add display and validation attributes as required. Note that I deleted the constructor (you don't seem to be using it, but if you did, then you also need to include a parameter-less constructor, otherwise an exception will be thrown when submitting to the POST method. I also assume that Level should be typeof int since you binding to the int ID property of Grade.

GET方法中的代码应为

The the code in your GET method should be

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")

还请注意，在POST方法中，由于ModelState无效，因此如果您返回视图，则需要重新分配SelectList.

Note also that in the POST method, your need to reassign the SelectList if you return the view because ModelState is invalid.

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