How to query flags stored as enum in NHibernate

Question

How to do either a HQL or a Criteria search (the latter is preferred) involving an enum that is used as flags. In other words, I have a persisted enum property that stores some kind of flags. I want to query all the records that have one of these flags set. Using Eq won't work of course because that will only be true, if that is the only flag set.

Solving this using the Criteria API would be the best, but if this is only doable using HQL that is good too.

Hygrometry

Answer 1

Here's how you could do it with the criteria API:

[Flags]
enum Bar{
   A = 0x01,
   B = 0x02,
   C = 0x04
}

var criteria = this.Session.CreateCriteria<Foo>()
            .Add( BitwiseFlags.IsSet( "Bar", Bar.A | Bar.C ) );

using:

public class BitwiseFlags : LogicalExpression
{
    private BitwiseFlags( string propertyName, object value, string op ) :
        base( new SimpleExpression( propertyName, value, op ),
        Expression.Sql( "?", value, NHibernateUtil.Enum( value.GetType() ) ) )
    {
    }

    protected override string Op
    {
        get { return "="; }
    }

    public static BitwiseFlags IsSet(string propertyName, Enum flags)
    {
        return new BitwiseFlags( propertyName, flags, " & " );
    }
}

should generate the following output where clause:

 FROM _TABLE
 WHERE  (this_.Bar & 5 = 5)

which should give you rows that have flags Bar.A and Bar.C set (excluding everything else). You should be able to use it with conjunction and disjunction too.

Ible

How can i do this with QueryOver? – Pucida

Found the perfect QueryOver solution at github.com/AndreasJilvero/NHibernate.Bitwise. Very grateful to have found that so could add to existing QueryOver queries as opposed to switching them over. Nice and clean implementation. – Trilby

Answer 2

HQL is easy:

var matching = session.CreateQuery(@"
                       from MyEntity
                       where FlagsProperty & :flag = :flag
                       ")
                      .SetParameter("flag", MyEnum.FlagValue)
                      .List<MyEntity>();

Lectureship

Is there a way of achieving the same using NHibernate LINQ ? I am trying to do something like this .... from obj in Session.Linq<MyEntity>() where ( obj.FlagsProperty & flag ) == ( flag ) select obj); ...where flag is the parameter but it is throwing exception "System.NullReferenceException : Object reference not set to an instance of an object" – Asta

Steve just answered this in the forum, deleting my previous reply – Lectureship

@Asta Did you find a way to do this with Linq? Thanks. – Grigson

Answer 3

Here is how I solved using Criteria:

Expression.Eq(
  Projections.SqlProjection("({alias}." + propertyname + " & " + 
    ((int)value).ToString() + ") as " + propertyname + "Result",
    new[] { propertyname + "Result" },
    new IType[] { NHibernateUtil.Int32 }
  ), value );

Hygrometry

Answer 4

You are looking for Expression.Or if you are querying 2 values or Expression.Disjunction if you are querying for more than 2 values:

criteria.Add(
  Expression.Disjunction()
    .Add(Expression.Eq("property", value1))
    .Add(Expression.Eq("property", value2))
    .Add(Expression.Eq("property", value3))
)

Emblematize