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Vasile Tomoiaga
Vasile Tomoiaga

Reputation: 1747

How to use flags enums in Linq to Entities queries?

I have a [Flags] enum like this:

[Flags]
public enum Status
{
  None = 0,
  Active = 1,
  Inactive = 2,
  Unknown = 4
}

A Status enum may contain two values such as: 

Status s = Status.Active | Status.Unknown;

Now I need to create a linq query (LINQ to ADO.NET Entities) and ask for records whose status is s above, that is Active or Unknown;

var result = from r in db.Records
             select r
             where (r.Status & (byte)s) == r.Status

Of course I get an error, because LINQ to Entities only knows to handle primitive types in the Where clause.

The error is:

Unable to create a constant value of type 'Closure type'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

Is there a workable way? I may have a status Enum with 10 possible values and to query for 5 of the statuses. How do I construct the query using Flags enum in an elegant way?

Thanks.

Update

This seems to be a Linq to Entities problem. I think in LINQ to SQL it works (not sure, didn't tested).

Upvotes: 5

Views: 12546

Answers (7)

Gökhan CANGÜL
Gökhan CANGÜL

Reputation: 11

In DB Flags enum must be integer. After that you can try it like this:

Status s = Status.Active | Status.Unknown;

var result = from r in db.Records
where (s & r.Status) == r.Status
select r

Upvotes: 1

Eat at Joes
Eat at Joes

Reputation: 5019

Just use HasFlag()

var result = from r in db.Records
         where r.Status.HasFlag(s)
         select r

Upvotes: 10

Ann
Ann

Reputation:

The folloiwng works for me in C#

    public const StatusTypes ActiveAlert = StatusTypes.Accepted | StatusTypes.Delivered;

        int flags = (int)ActiveAlert;

        try
        {
            var query = from p in model.AlertsHistory
                        where (p.UserId == clientId
                        && (p.Status.HasValue && (p.Status.Value & flags) != 0))
                        select p;
            var aList = query.ToList();

            return (aList);


        }
        catch (Exception exc)
        {
            log.Error("Exception getting Alerts History for user.", exc);
            throw;
        }

Upvotes: 0

Yannick Motton
Yannick Motton

Reputation: 36031

I am unsure if a bitwise AND-operation will work, but try casting s to an int:

        int i = (int)s;
        var result = from r in db.Records
             select r
             where (r.Status & i) == r.Status

Which database engine are you using? Possibly the engine does not support bitwise operations.

Reference: http://www.matthidinger.com/archive/2008/02/26/entity-framework-comparison-frustration-explained.aspx

Upvotes: 0

LukeH
LukeH

Reputation: 269618

Try it like this:

byte status = (byte)(Status.Active | Status.Unknown);

var result = from r in db.Records
             select r
             where (r.Status & status) != 0

Upvotes: 0

iburlakov
iburlakov

Reputation: 4232

var result = from r in db.Records
             where r.Status == s
             select r

Upvotes: 1

erikkallen
erikkallen

Reputation: 34421

I don't know EF, but could inserting additional casts work?

var result = from r in db.Records
             where ((byte)r.Status & (byte)s) == (byte)r.Status
             select r

Upvotes: 0

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