Enum as Class Property

问题:

I have a class for something simple, Status, and it contains two properties. I want to use an Enum for one of the Properties(StatusID) so that I can eliminate a bunch of Magic Strings.

My question is how I then work with it, for example: I have a Method that returns a List for binding in a dropdown box that looks like this -->

public static IList<Status> GetAdminStatuses()
{
  IQueryable<Status> stat=context.tblAdminStatus
       .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
       .Select(s => new Status()
       {
         StatusID=s.StatusID,
         StatusDescription=s.StatusDesc
       });
   return stat.ToList();
}

It obviously does not like my StatusID=s.StatusID part as the DB stores it as a varchar. Am I missing something simple here or have I stumbled into noob territory and should not be doing it this way?

For reference here is the Class and Enum:

public class Status
{
  public string StatusID {get; set;}
  public string StatusDescription {get; set;}
}

public enum MyStatusID
{
  draft, pending, declined, accepted, close 
}

---

EDIT

So taking the advice here I was able to get my method to compile however at runtime I get the following --> Method 'System.Object Parse(System.Type, System.String)' has no supported translation to SQL.

Thoughts?

---

EDIT - Method in it's entirety by request, thanks (NOTE that NoaStatusID == MyStatusID)

   public static IList<Status> GetAdminStatuses(NoaStatusID currentStatus = NoaStatusID.draft)
    {
        using (var context = MemberDataContext.Create())
        {
            IQueryable<Status> stat=context.tblAdminStatus
                   .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
                   .Select(s => new Status()
                     {
                       StatusID=NoaStatusID)Enum.Parse(typeof(NoaStatusID),s.StatusID),
                       StatusDescription=s.StatusDesc
                     });

            switch (currentStatus)
            {
                case NoaStatusID.draft:
                    stat=stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending));                                                     
                    break;
                case NoaStatusID.pending:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.accepted || s.StatusID ==NoaStatusID.declined || s.StatusID ==NoaStatusID.pending));
                    break;                        
                case NoaStatusID.declined:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending || s.StatusID == NoaStatusID.declined));
                    break;
                case NoaStatusID.accepted:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.accepted));
                    break;
                case NoaStatusID.mailed:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal));
                    break;
                case NoaStatusID.monitor:
                case NoaStatusID.appeal:
                case NoaStatusID.close:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal));   
                    break;                    
            }


            return stat.ToList();
        }
    }

回答1:

i believe what you're searching for is:

StatusID = (MyStatusID)Enum.Parse(typeof(MyStatusID), s.StatusID),

in .Net 4.0 there is also a Enum.TryParse(string, out enum) but that is not so useful inside your .Select()

Alternatively: albeit less efficient in most cases, you can keep the Status.StatusID as a string and add a readonly property StatusEnum that outputs the Enum value on the fly:

public MyStatusID StatusEnum {
    get {
        return (MyStatusID)Enum.Parse(typeof(MyStatusID), StatusID)
    }

    private set;
}

in .Net 4.0:
public MyStatusID StatusEnum {
    get {
        MyStatusID value;
        if(!Enum.TryParse(StatusID, out value)
          value = MyStatusID.Default; // default value, instead of Exception throwing

        return value;
    }

    private set;
}

this alternative re-parses the value everytime instance.StatusEnum is read, so I don't recommend it unless LINQ hates the first approach

---

Responding to your last EDIT:

The Enum.Parse() is translating to SQL fine in your example. The problem is in the switch statement where you're adding on a .Where() clause that has a comparison with an Enum. LINQ doesn't know how to turn an Enum == Enum into SQL but it does know to do it with C# objects. So the easiest solution is to ToList() them and do the comparison locally. Unfortunately, that means it's downloading rows of -all- Status types from the database and then filters them locally. If you have millions of records this may not be reasonable:

   public static IList<Status> GetAdminStatuses(NoaStatusID currentStatus = NoaStatusID.draft)
    {
        using (var context = MemberDataContext.Create())
        {
            List<Status> stat=context.tblAdminStatus
                   .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
                   .Select(s => new Status()
                     {
                       StatusID=NoaStatusID)Enum.Parse(typeof(NoaStatusID),s.StatusID),
                       StatusDescription=s.StatusDesc
                     })
                   .ToList();

            switch (currentStatus)
            {
                case NoaStatusID.draft:
                    stat=stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending)).ToList();                                                     
                    break;
                case NoaStatusID.pending:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.accepted || s.StatusID ==NoaStatusID.declined || s.StatusID ==NoaStatusID.pending)).ToList();
                    break;                        
                case NoaStatusID.declined:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.draft || s.StatusID == NoaStatusID.pending || s.StatusID == NoaStatusID.declined)).ToList();
                    break;
                case NoaStatusID.accepted:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.accepted)).ToList();
                    break;
                case NoaStatusID.mailed:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.mailed || s.StatusID == NoaStatusID.monitor || s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal)).ToList();
                    break;
                case NoaStatusID.monitor:
                case NoaStatusID.appeal:
                case NoaStatusID.close:
                    stat = stat.Where(s => (s.StatusID == NoaStatusID.close || s.StatusID == NoaStatusID.appeal)).ToList();   
                    break;                    
            }


            return stat;
        }
    }

回答2:

Isn't what you are looking for?

 Colors colorValue = (Colors) Enum.Parse(typeof(Colors), colorString);

回答3:

If you make the backing field* an int, it will work just fine.

In fact you can even use byte enums (with a smallint backing field).

There is a problem with the designer however. IIRC, the enum declaration needs to be in the same namespace.

Note: By backing field, I mean the database table column type.

回答4:

My guess is that you want the String equivalent of the enum value, but it isn't very clear:

public static IList<Status> GetAdminStatuses()
{
  IQueryable<Status> stat=context.tblAdminStatus
       .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
       .Select(s => new Status()
       {
         StatusID=Enum.GetName(typeof(MyStatusID),s.StatusID),
         StatusDescription=s.StatusDesc
       });
}

EDIT: Given the comments, sounds like you want:

public static IList<Status> GetAdminStatuses()
{
  IQueryable<Status> stat=context.tblAdminStatus
       .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
       .Select(s => new Status()
       {
         StatusID=(MyStatusID)s.StatusID,
         StatusDescription=s.StatusDesc
       });
}

EDIT: Given the (further) comments, sounds like you want:

public static IList<Status> GetAdminStatuses()
{
  IQueryable<Status> stat=context.tblAdminStatus
       .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
       .Select(s => new Status()
       {
         // If database is storing 'draft' (as a varchar)
         StatusID=Enum.Parse(typeof(MyStatusID), s.StatusID),
         StatusDescription=s.StatusDesc
       });
}

Or maybe

public static IList<Status> GetAdminStatuses()
{
  IQueryable<Status> stat=context.tblAdminStatus
       .Where(s => s.InactiveDate > DateTime.Now || s.InactiveDate == null)
       .Select(s => new Status()
       {
         // If database is storing '0' (as a varchar)
         StatusID=(MyStatusID)int.Parse(s.StatusID),
         StatusDescription=s.StatusDesc
       });
}