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.D iscriminator==" Domestics")]
class DomesticsSuppli er {
public string Discriminator { get; set; };
public string Name { get; set; };
}

class QueryAttribute< TEntity: Attribute {
IQueryable<TEnt ityQuery;
internal QueryAttribute( IQueryable<TEnt ityquery) {
Query = query;
}
}

[Marc Gravell]

Re: Lambda expression in dlinq attribute

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="Supp lierDiscriminat or",
Type=typeof(Sup plier)]
....
public static Expression<Func <Supplier, bool>SupplierDi scriminator {
get {return d=d.Discriminat or=="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]

Re: Lambda expression in dlinq attribute

Additional; my unserstanding is that EF supports much better
inheritance than LINQ-to-SQL; a taster is here:

http://blogs.msdn.com/adonet/archive/2007/03/15/inheritance-in-the-entity-framework.aspx

Marc

[Marc Gravell]

Re: Lambda expression in dlinq attribute

Also:

http://dotnetaddict.dotnetdevelopersjournal.com/adoef_entityinheritancewoes.htm

[Marc Gravell]

Re: Lambda expression in dlinq attribute

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

[Marc Gravell]

Re: Lambda expression in dlinq attribute

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...