Lambda expression in dlinq attribute

[Andrus]

I need to use lambda expressions or other way to
specify default query for dlinq entity type.
Code below causes compile error shown in comment.
How to fix ?
Maybe to use [QueryAttribute( "Supplier", "d=>
d.Discriminator==""Domestics"" ")] ?

Andrus.

using System;
using System.Linq;

// '<' unexpected : attributes cannot be generic
[QueryAttribute<Supplier>(d=d.Discriminator=="Domes tics")]
class DomesticsSupplier {
public string Discriminator { get; set; };
public string Name { get; set; };
}

class QueryAttribute<TEntity: Attribute {
IQueryable<TEntityQuery;
internal QueryAttribute(IQueryable<TEntityquery) {
Query = query;
}
}

[Marc Gravell]

Well, the compiler message is clear enough; you would have to pass a
Type through, not a generic. Also, your lambda isn't an IQueryable<T>
- it is a Func<T, boolor an Expression<Func<T, bool>- but I doubt
you could use iether directly in an attribute.

I would suggest something like
[QueryAttrubute(Condition="SupplierDiscriminator",
Type=typeof(Supplier)]
....
public static Expression<Func<Supplier, bool>SupplierDiscriminator {
get {return d=d.Discriminator=="Domestics";}
}

(I would make Type optional, defaulting to the current)

Note that this usage is very different (as I understand it) to how
NHibernate uses QueryAttribute, and you'll need to code it up by
hand...

Marc

[Marc Gravell]

Additional; my unserstanding is that EF supports much better
inheritance than LINQ-to-SQL; a taster is here:
http://blogs.msdn.com/adonet/archive...framework.aspx

Marc

[Marc Gravell]

Also:
http://dotnetaddict.dotnetdevelopers...itancewoes.htm

[Marc Gravell]

Actually, it looks like LINQ to SQL supports
InheritanceMappingAttribute, and IsDiscriminator on ColumnAttribute.

[Marc Gravell]

Well, since .NET has single inheritance, you can't have two dimensions
of discriminator... could you perhaps simply map the two columns into
a single discriminator column? This sound like something EF could
handle (perhaps), or maybe a UDF when reading... but to be honest I
think two discriminators is making life hard...