Validation message won't appear - accepts 'please select' as an entry - asp.net-mvc

Question

I am submiting a blank form and all of the other fields display their correct validation error message stating that the field cannot be empty, except for one.
Here is the model:
public enum Medium
{
[Description("Teleconference & Report")]
Teleconference_Report,
[Description("Email & Telephone")]
Email_Telephone
}
[Required]
[Display(Name = "Medium")]
public Medium Medium { get; set; }
Here is the field in the form:
<div class="form-group">
#Html.LabelFor(model => model.Medium, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-5">
#Html.DropDownList("MediumID", null, "Please select...", htmlAttributes: new { #class = "form-control" })
#Html.ValidationMessageFor(model => model.Medium, "", new { #class = "text-danger" })
</div>
</div>
The "MediumID" DropDownList is populated using a viewbag which is set to whatever the following returns:
// Puts all of the mediums of communication into a user friendly dropdownlist.
public List<SelectListItem> GetMediumList()
{
List<SelectListItem> mediumList = new List<SelectListItem>();
foreach (Medium state in EnumToList<Medium>())
{
mediumList.Add(new SelectListItem
{
Text = GetEnumDescription(state),
Value = state.ToString(),
});
}
return mediumList;
}
The issue is, is that when the default display of the drop down list of 'please select...' is left, this is accepted and the form gets submitted, which doesn't happen for any of my other fields. When looking at the new entry in the database, the 'Medium' field gets set to the first thing in the DropDownList which is 'Teleconference & Report'.
Any help is greatly appreciated.
EDIT:
Below shows the form section for another enum called 'Frequency', but these are not changed to user friendly strings.
<div class="form-group">
#Html.LabelFor(model => model.Frequency, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-5">
#Html.EnumDropDownListFor(model => model.Frequency, "Please select...", htmlAttributes: new { #class = "form-control" })
#Html.ValidationMessageFor(model => model.Frequency, "", new { #class = "text-danger" })
</div>
</div>
Below here, shows the two methods which turn the enums into user friendly strings:
// Returns a 'user friendly', readable version of the enum.
public static string GetEnumDescription(Enum value)
{
FieldInfo fi = value.GetType().GetField(value.ToString());
DescriptionAttribute[] attributes =
(DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attributes != null && attributes.Length > 0)
return attributes[0].Description;
else
return value.ToString();
}
// Puts all of the same enums into a list.
public static IEnumerable<T> EnumToList<T>()
{
Type enumType = typeof(T);
// Can't use generic type constraints on value types,
// so have to do check like this.
if (enumType.BaseType != typeof(Enum))
throw new ArgumentException("T must be of type System.Enum");
Array enumValArray = Enum.GetValues(enumType);
List<T> enumValList = new List<T>(enumValArray.Length);
foreach (int val in enumValArray)
{
enumValList.Add((T)Enum.Parse(enumType, val.ToString()));
}
return enumValList;
}

Answer 1

Add the EnumDataType attribute to the property on your view model:
[EnumDataType(typeof(Medium), ErrorMessage = "Submitted value is not valid for the enum")]
public Medium Medium { get; set; }
You should add this anyway, because an Enum can represent any numeric value and won't be validated automatically by the MVC framework.
I hope this helps!