Enums in Model Classes

One application of enum types is to represent categories of objects. We will take this approach in our CodingEvents application to categorize events based on their type, such as conference or meetup.

To follow along in CodingEvents, make sure that you have forked and cloned our repo . Your code at the beginning of this chaper should look like the viewmodels branch and at the end, your code should look like the enums branch.

Enum Types in Models

Create an Enum Class

In your Models directory within CodingEvents, create a new class called EventType. Replace the class keyword with enum and delete the default constructor.

Each value is demarcated with a comma.

EventType:

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   public enum EventType
   {
      Conference,
      Meetup,
      Workshop,
      Social
   }

Add an Enum Property to a Model Class

Other objects can have enum type properties. To add an EventType property to our model Event, we create a Type property in Event amongst the other properties declared:

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   // other Event property declarations

   public EventType Type { get; set; }

   // Event methods

Once we have added an EventType property to our model, we need to add an EventType property to our ViewModel.

Add an Enum Property to a ViewModel

The first thing we need to do is add an EventType property to AddEventViewModel.

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   // other AddEventViewModel property declarations

   public EventType Type { get; set; }

Now that we have a property to hold the event type that the user selects, we need to create a list of all of the possible event types. We will use this list to populate the select element in a later step.

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   public List<SelectListItem> EventTypes { get; set; } = new List<SelectListItem>
   {
      new SelectListItem(EventType.Conference.ToString(), ((int)EventType.Conference).ToString()),
      new SelectListItem(EventType.Meetup.ToString(), ((int)EventType.Meetup).ToString()),
      new SelectListItem(EventType.Social.ToString(), ((int)EventType.Social).ToString()),
      new SelectListItem(EventType.Workshop.ToString(), ((int)EventType.Workshop).ToString())
   };

Because the EventType options are not changing, we can populate this property with a default value. We add each of the constants to the EventTypes list. SelectListItem is an ASP.NET-provided class that represents each <option> element in a <select> element. The SelectListItem constructor requires a Text and Value property assignment. The Text property sets the displayed text in the <option> tag. This is created by getting each EventType and casting it to a string type. The Value property sets the value attribute on the <option> tag. This is created by getting each EventType, casting it to its implicit int value, and then casting that to a string type.

This list only exists in AddEventViewModel because we need it only for the purposes of displaying all of the options. We do not need a list of the different event types in our Event model. We just need the type of one event. This is another great reason to use a ViewModel!

Pass Enum Values Through the Controller

In EventsController, the Add() action method that responds to POST requests uses model binding to create an AddEventViewModel object. So like any other field on the model, the controller does not necessarily need to know about the addition of AddEventViewModel.Type in order to create an AddEventViewModel instance from a form. However, we need to make sure that we are properly setting the Type property of our Event object using the value from the Type property of our AddEventViewModel object.

In EventsController:

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   Event newEvent = new Event
   {
      Name = addEventViewModel.Name,
      Description = addEventViewModel.Description,
      ContactEmail = addEventViewModel.ContactEmail,
      Type = addEventViewModel.Type
   };

Use Enum Value in a select Element

The list of constants returned from EventType lends itself well to a select-type form input. We’ll update our form so that a user will have the option to choose one of the provided event types from a dropdown menu.

In Events/Add.cshtml:

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   <div class="form-group">
      <label asp-for="Type">Event Type</label>
      <select asp-for="Type" asp-items="Model.EventTypes"></select>
   </div>

As with the other form inputs on the page, the asp-for attribute determines the name and id attributes for the select tag. We also use asp-items to access all of the items stored in the list of our different enum values.

View the Event Type in the Events Table

Once an event is created, to display its Type property in the table of all events, we’ll modify Events/Index.cshtml to include another column:

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   <table class="table">
      <tr>
         <th>
            Id
         </th>
         <th>
            Name
         </th>
         <th>
            Description
         </th>
         <th>
            Contact Email
         </th>
         <th>
            Event Type
         </th>
      </tr>
      @foreach (var evt in Model)
      {
         <tr>
            <td>@evt.Id</td>
            <td>@evt.Name</td>
            <td>@evt.Description</td>
            <td>@evt.ContactEmail</td>
            <td>@evt.Type</td>
         </tr>
      }
   </table>