5

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).

Vasile Tomoiaga
  • 1,727
  • 3
  • 16
  • 19
  • You're query (if it worked) would only return those records whose status is simultaneously `Active` *and* `Unknown`. Is that what you want? – LukeH Sep 15 '09 at 11:40
  • No, it was a OR not an AND. So 'Status s = Status.Active | Status.Unknown;' is correct. Thanks! – Vasile Tomoiaga Sep 15 '09 at 11:42
  • @Vasi: That part is correct, but "`Status.Active|Status.Unknown`" is equivalent to "`1|4`" which is `5`. So your `where` clause is effectively saying "`where (r.Status & 5) == r.Status`", which is the same as "`where r.Status == 5`", which is the same as saying (in English) "where `r.Status` is both `Active` *and* `Unknown`"! – LukeH Sep 15 '09 at 11:50
  • You can convert your entities to enumerables. See : http://stackoverflow.com/a/13954549/616274 – Eric Bole-Feysot Dec 20 '12 at 10:16
  • As of EF6.1 `HasFlag` is supported in LINQ-to-Entities. See: http://data.uservoice.com/forums/72025-entity-framework-feature-suggestions/suggestions/3951293-support-enum-hasflag and https://entityframework.codeplex.com/workitem/1497 – Shay Feb 17 '15 at 02:00

7 Answers7

10

Just use HasFlag()

var result = from r in db.Records
         where r.Status.HasFlag(s)
         select r
Eat at Joes
  • 4,937
  • 1
  • 40
  • 40
2

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
Alicia
  • 1,152
  • 1
  • 23
  • 41
Gökhan CANGÜL
  • 21
  • 1
1
var result = from r in db.Records
             where r.Status == s
             select r
iburlakov
  • 4,164
  • 7
  • 38
  • 40
0

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
erikkallen
  • 33,800
  • 13
  • 85
  • 120
  • r.Status is byte already, and I added the cast in te question also. This is not the problem, the problem is that it will not run. It compiles but doesn't run. See the error in the question. – Vasile Tomoiaga Sep 15 '09 at 11:38
0

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
LukeH
  • 263,068
  • 57
  • 365
  • 409
  • I think the evaluation in Where is not translatable to esql or somethong like that. That's why I get the exception: "Unable to create a constant value of type 'Closure type'. Only primitive types ('such as Int32, String, and Guid') are supported in this context." – Vasile Tomoiaga Sep 15 '09 at 11:40
0

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

Yannick Motton
  • 34,761
  • 4
  • 39
  • 55
  • Using LINQ to Entities over a MS SQL Server. – Vasile Tomoiaga Sep 15 '09 at 12:25
  • No, it is a problem that it cannot translate the result of the enum to a native SQL type. Thus using an integer comparison might work. – Yannick Motton Sep 15 '09 at 12:39
  • I think it cannot translate the bit comparison into eSql. I used the cast to byte in my code before posting this question, but I missed it when I wrote the short example here. So it is not a cast problem, I think it is a bit comparison problem, not being supported bu EF. – Vasile Tomoiaga Sep 15 '09 at 14:02
  • what is the datatype of the Status column? – Yannick Motton Sep 15 '09 at 14:54
  • Still, please try a cast to `int`. This is really all about finding a workaround for EF LINQ->SQL translator deficiency... you have to try the corner cases. – Pavel Minaev Sep 16 '09 at 20:14
0

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;
        }