问题
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) 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) 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 ?
MY MODELS
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; }
}
View Model
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);
}
}
MY CONTEXT CLASS
public class EmployeeContext : DbContext
{
public DbSet<Employee> Employees { get; set; }
public DbSet<Department> Departments { get; set; }
public DbSet<Grade> Grades { get; set; }
}
MY CONTROLLER
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);
}
}
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" />
}
回答1:
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
.
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; }
}
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
.
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);
and in the view
@Html.DropDownListFor(x => Model.Level, Model.Grades, "Select Level")
Note also that in the POST method, your need to reassign the SelectList
if you return the view because ModelState
is invalid.
回答2:
You can use the following approach that populates three DropDownListFor at the same View:
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; }
}
Controller:
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);
}
View:
@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" })
Hope this helps...
来源:https://stackoverflow.com/questions/42549622/populate-dropdownlist-in-asp-net-mvc-from-database-table-using-entity-framework