Get Display Enum in LINQ

Question

How get a display/description enum in LINQ query?

For example

 var query = dbo.Records.AsQueryable()
              .Select(x => new
              {
                  Id = x.Id,
                  Care = new
                  {
                      x.StartDate,
                      x.ForwardedBy,
                  },
                  Prescriptions = x.Prescriptions.Select(p => new
                  {
                      p.Medicament,
                      p.IntervalUse //My Enum, how get Display name?
                  }),
              }).OrderByDescending(x => x.Id);

This query is an exampleand I need to be AsQueryable to generate faster query in my database

Any reason you can't just keep it as the enum and get the display name in your view or in your form? That would, generally, be the preferred method. — Josh K
– Josh K, Commented Jul 27, 2016 at 21:42
What do you mean Display/description? do you have [DisplayNameAttribute]s on your enum, or are you talking about the enum's name — Sam I am says Reinstate Monica
– Sam I am says Reinstate Monica, Commented Jul 27, 2016 at 21:44
@SamIam Yes, i use DisplayNameAttribute and i can get DisplayName value in Linq query — user98498
– user98498, Commented Jul 27, 2016 at 21:53
Can't you just do a tostring that should return the name of the that enum value as a string? p.IntervalUse.ToString() — Charles McIntosh
– Charles McIntosh, Commented Jul 27, 2016 at 22:00

X3074861X · Accepted Answer · 2016-07-27 22:02:20Z

1

It may not be a bad idea to write an enum extension method if it's something you're going to need often :

public static string Describe(this Enum enumVal)
{
    var type = enumVal.GetType();
    var memInfo = type.GetMember(enumVal.ToString());
    var attributes = memInfo[0].GetCustomAttributes(typeof(DescriptionAttribute), false);
    return (attributes.Length > 0) ? ((DescriptionAttribute)(attributes[0])).Description : enumVal.ToString();
}

answered Jul 27, 2016 at 22:02

X3074861X

3,8296 gold badges34 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Josh K · Accepted Answer · 2016-07-27 22:51:36Z

Since LINQ doesn't know about that extension method, you will have to enumerate first, then get the attribute using reflection.

public static class EnumExtensions
{
    public static string GetDisplayName(this Enum value)
    {
        var attribute = (DisplayNameAttribute) value.GetType()
            .GetField(value.ToString())
            .GetCustomAttributes(false)
            .Where(a => a is DisplayNameAttribute)
            .FirstOrDefault();

        return attribute != null ? attribute.DisplayName : value.ToString();
    }
}

I can't test this right now, but you may try this and let us know if it works:

var query = dbo.Records.Include(x => x.Prescriptions).OrderByDescending(x => x.Id).AsEnumerable()
            .Select(x => new
            {
                Id = x.Id,
                Care = new
                {
                    x.StartDate,
                    x.ForwardedBy,
                },
                Prescriptions = x.Prescriptions.Select(p => new
                {
                    p.Medicament,
                    p.IntervalUse.GetDisplayName()
                }),
            });

You can't use it in a LINQ query unless you have already enumerated the IQueryable because there is no mapping in LINQ to Entities for this.
Wtf? why ef have enum support, if not have support a linq enum? :|
It has enum support, but it doesn't know anything about the attributes you have on the enum or enum values, so it cannot map the extension method I provided to SQL or whatever back end you are using.
Other solution Josh? I can generate my sql query for faster query, use ToList() or AsEnumerable is slow

Sam I am says Reinstate Monica · Accepted Answer · 2016-07-27 22:34:26Z

0

I'd use the System.Reflection libraries.

public static GetMyEnumDisplayName(MyEnumType value)
{
    var displayAttribute = value.GetType()
        .GetTypeInfo()
        .GetDeclaredField(result)
        .GetCustomAttribute(typeof(DisplayAttribute));

        if (displayAttribute != null)
        {
            var Name = ((DisplayAttribute)displayAttribute).Name;
        }
}

That's not supported in linq to entities, but you can instead make that a helper property in your view model.

Your first step is to select a view model instead of an anonymous object the next step is to add a function in the setter

public string EnumDisplayValue { get { return GetMyEnumDisplayName(MyEnumValue); } }

edited Jul 27, 2016 at 22:34

answered Jul 27, 2016 at 21:57

Sam I am says Reinstate Monica

31.3k12 gold badges74 silver badges101 bronze badges

3 Comments

user98498 Over a year ago

How i use in linq query?

Sam I am says Reinstate Monica Over a year ago

@user98498 make that code into a method and call that method from the linq query

Sam I am says Reinstate Monica Over a year ago

@user98498 what's happening?

Lucian Bumb · Accepted Answer · 2016-07-28 01:53:11Z

why you do not go for the simplest way:

public enum IntervalUse
    {
        Hourly,
        Daily,
        Weekly
    }

    public static class EnumExt
    {
        public static string GetDescription(this IntervalUse item)
        {
            switch (item)
            {
                case IntervalUse.Hourly:
                    return "Hour by hour";
                case IntervalUse.Daily:
                    return "Day by day";
                case IntervalUse.Weekly:
                    return "Each week ...";
                default:
                    throw new ArgumentOutOfRangeException(nameof(item), item, null);
            }
        }
    }

then you can call in your query : p.IntervalUse.GetDescription()

Collectives™ on Stack Overflow

Get Display Enum in LINQ

4 Answers 4

Comments

6 Comments

3 Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

6 Comments

3 Comments

Comments

Related