使用Entity Framework 6和ViewModel从数据库表填充ASP.NET MVC中的DropDownList

Question

对于我可以使用ajax/jquery和存储过程快速完成的问题,我一直在摸不着头脑.我想要

1)使用Entity Framework和视图模型从数据库表中获取的值填充下拉列表.我不想使用VIEWBAG或VIEWDATA.任何帮助赞赏.

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？

我的模特

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);
    }
}

我的上下文课程

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

@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

主要的问题是,在视图中,您有new SelectList(Model.Grades, "ID", "Level"),但Grades就是IEnumerable<SelectListItem>和SelectListItem不包含命名属性ID和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,而应该是视图模型

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构造函数,否则在提交POST方法时会抛出异常.我还假设这Level应该TYPEOF int因为您有约束力的int ID财产Grade.

你的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,SelectList如果返回视图,ModelState则需要重新分配,因为它无效.