I need some help with the select tag helper in ASP.NET Core.
I have a list of employees that I'm trying to bind to a select tag helper. My employees are in a List<Employee> EmployeesList
and selected value will go into EmployeeId
property. My view model looks like this:
public class MyViewModel
{
public int EmployeeId { get; set; }
public string Comments { get; set; }
public List<Employee> EmployeesList {get; set; }
}
My employee class looks like this:
public class Employee
{
public int Id { get; set; }
public string FullName { get; set; }
}
My question is how do I tell my select tag helper to use the Id
as the value while displaying FullName
in the drop down list?
<select asp-for="EmployeeId" asp-items="???" />
I'd appreciate some help with this. Thanks.
In your GET action, create an object of your view model, load the EmployeeList
collection property and send that to the view.
public IActionResult Create()
{
var vm = new MyViewModel();
vm.EmployeesList = new List<Employee>
{
new Employee { Id = 1, FullName = "Shyju" },
new Employee { Id = 2, FullName = "Bryan" }
};
return View(vm);
}
And in your create view, create a new SelectList
object from the EmployeeList
property and pass that as value for the asp-items
property.
@model MyViewModel
<form asp-controller="Home" asp-action="Create">
<select asp-for="EmployeeId"
asp-items="@(new SelectList(Model.EmployeesList,"Id","FullName"))">
<option>Please select one</option>
</select>
<input type="submit"/>
</form>
And your HttpPost action method to accept the submitted form data.
[HttpPost]
public IActionResult Create(MyViewModel model)
{
// check model.EmployeeId
// to do : Save and redirect
}
Or
If your view model has a List<SelectListItem>
as the property for your dropdown items.
public class MyViewModel
{
public int EmployeeId { get; set; }
public string Comments { get; set; }
public List<SelectListItem> Employees { set; get; }
}
And in your get action,
public IActionResult Create()
{
var vm = new MyViewModel();
vm.Employees = new List<SelectListItem>
{
new SelectListItem {Text = "Shyju", Value = "1"},
new SelectListItem {Text = "Sean", Value = "2"}
};
return View(vm);
}
And in the view, you can directly use the Employees
property for the asp-items
.
@model MyViewModel
<form asp-controller="Home" asp-action="Create">
<label>Comments</label>
<input type="text" asp-for="Comments"/>
<label>Lucky Employee</label>
<select asp-for="EmployeeId" asp-items="@Model.Employees" >
<option>Please select one</option>
</select>
<input type="submit"/>
</form>
The class SelectListItem
belongs to Microsoft.AspNet.Mvc.Rendering
namespace.
Make sure you are using an explicit closing tag for the select element. If you use the self closing tag approach, the tag helper will render an empty SELECT element!
The below approach will not work
<select asp-for="EmployeeId" asp-items="@Model.Employees" />
But this will work.
<select asp-for="EmployeeId" asp-items="@Model.Employees"></select>
The above examples are using hard coded items for the options. So i thought i will add some sample code to get data using Entity framework as a lot of people use that.
Let's assume your DbContext object has a property called Employees
, which is of type DbSet<Employee>
where the Employee
entity class has an Id
and Name
property like this
public class Employee
{
public int Id { set; get; }
public string Name { set; get; }
}
You can use a LINQ query to get the employees and use the Select method in your LINQ expression to create a list of SelectListItem
objects for each employee.
public IActionResult Create()
{
var vm = new MyViewModel();
vm.Employees = context.Employees
.Select(a => new SelectListItem() {
Value = a.Id.ToString(),
Text = a.Name
})
.ToList();
return View(vm);
}
Assuming context
is your db context object. The view code is same as above.
Some people prefer to use SelectList
class to hold the items needed to render the options.
public class MyViewModel
{
public int EmployeeId { get; set; }
public SelectList Employees { set; get; }
}
Now in your GET action, you can use the SelectList
constructor to populate the Employees
property of the view model. Make sure you are specifying the dataValueField
and dataTextField
parameters.
public IActionResult Create()
{
var vm = new MyViewModel();
vm.Employees = new SelectList(GetEmployees(),"Id","FirstName");
return View(vm);
}
public IEnumerable<Employee> GetEmployees()
{
// hard coded list for demo.
// You may replace with real data from database to create Employee objects
return new List<Employee>
{
new Employee { Id = 1, FirstName = "Shyju" },
new Employee { Id = 2, FirstName = "Bryan" }
};
}
Here I am calling the GetEmployees
method to get a list of Employee objects, each with an Id
and FirstName
property and I use those properties as DataValueField
and DataTextField
of the SelectList
object we created. You can change the hardcoded list to a code which reads data from a database table.
The view code will be same.
<select asp-for="EmployeeId" asp-items="@Model.Employees" >
<option>Please select one</option>
</select>
Sometimes you might want to render a select element from a list of strings. In that case, you can use the SelectList
constructor which only takes IEnumerable<T>
var vm = new MyViewModel();
var items = new List<string> {"Monday", "Tuesday", "Wednesday"};
vm.Employees = new SelectList(items);
return View(vm);
The view code will be same.
Some times,you might want to set one option as the default option in the SELECT element (For example, in an edit screen, you want to load the previously saved option value). To do that, you may simply set the EmployeeId
property value to the value of the option you want to be selected.
public IActionResult Create()
{
var vm = new MyViewModel();
vm.Employees = new List<SelectListItem>
{
new SelectListItem {Text = "Shyju", Value = "11"},
new SelectListItem {Text = "Tom", Value = "12"},
new SelectListItem {Text = "Jerry", Value = "13"}
};
vm.EmployeeId = 12; // Here you set the value
return View(vm);
}
This will select the option Tom in the select element when the page is rendered.
If you want to render a multi select dropdown, you can simply change your view model property which you use for asp-for
attribute in your view to an array type.
public class MyViewModel
{
public int[] EmployeeIds { get; set; }
public List<SelectListItem> Employees { set; get; }
}
This will render the HTML markup for the select element with the multiple
attribute which will allow the user to select multiple options.
@model MyViewModel
<select id="EmployeeIds" multiple="multiple" name="EmployeeIds">
<option>Please select one</option>
<option value="1">Shyju</option>
<option value="2">Sean</option>
</select>
Similar to single select, set the EmployeeIds
property value to the an array of values you want.
public IActionResult Create()
{
var vm = new MyViewModel();
vm.Employees = new List<SelectListItem>
{
new SelectListItem {Text = "Shyju", Value = "11"},
new SelectListItem {Text = "Tom", Value = "12"},
new SelectListItem {Text = "Jerry", Value = "13"}
};
vm.EmployeeIds= new int[] { 12,13} ;
return View(vm);
}
This will select the option Tom and Jerry in the multi select element when the page is rendered.
If you do not prefer to keep a collection type property to pass the list of options to the view, you can use the dynamic ViewBag to do so.(This is not my personally recommended approach as viewbag is dynamic and your code is prone to uncatched typo errors)
public IActionResult Create()
{
ViewBag.Employees = new List<SelectListItem>
{
new SelectListItem {Text = "Shyju", Value = "1"},
new SelectListItem {Text = "Sean", Value = "2"}
};
return View(new MyViewModel());
}
and in the view
<select asp-for="EmployeeId" asp-items="@ViewBag.Employees">
<option>Please select one</option>
</select>
It is same as above. All you have to do is, set the property (for which you are binding the dropdown for) value to the value of the option you want to be selected.
public IActionResult Create()
{
ViewBag.Employees = new List<SelectListItem>
{
new SelectListItem {Text = "Shyju", Value = "1"},
new SelectListItem {Text = "Bryan", Value = "2"},
new SelectListItem {Text = "Sean", Value = "3"}
};
vm.EmployeeId = 2; // This will set Bryan as selected
return View(new MyViewModel());
}
and in the view
<select asp-for="EmployeeId" asp-items="@ViewBag.Employees">
<option>Please select one</option>
</select>
The select tag helper method supports grouping options in a dropdown. All you have to do is, specify the Group
property value of each SelectListItem
in your action method.
public IActionResult Create()
{
var vm = new MyViewModel();
var group1 = new SelectListGroup { Name = "Dev Team" };
var group2 = new SelectListGroup { Name = "QA Team" };
var employeeList = new List<SelectListItem>()
{
new SelectListItem() { Value = "1", Text = "Shyju", Group = group1 },
new SelectListItem() { Value = "2", Text = "Bryan", Group = group1 },
new SelectListItem() { Value = "3", Text = "Kevin", Group = group2 },
new SelectListItem() { Value = "4", Text = "Alex", Group = group2 }
};
vm.Employees = employeeList;
return View(vm);
}
There is no change in the view code. the select tag helper will now render the options inside 2 optgroup items.