I apologize in advance if this is the wrong forum to post this in, didn't see any forum's description mentioning LINQ.

I am getting the following exception:

The member '[MyBusinessClass].ID' has no supported translation to SQL.

For starters, this isn't even a Linq to Sql class. Am I wrong to assume that I can plug an object into an IQueryable collection and query it as I would a database?

Edit: When I try the following line of code everything works fine
this._repository.GetNewsPosts().ToList().AsQueryable().WithID(someGuid);
But this still does not:
this._repository.GetNewsPosts().WithID(someGuid);
See below for the meat of the GetNewsPosts and WithID methods.

The whole of what is happening makes it more odd.  I am running some unit tests on a website I am working on.  I wanted to do it all in LINQ to learn the new language features in 3.5.  I have a Service class and a Repository class.  The service has convenience methods like GetItemsById(guid id) which maps to a call to repository that gets an IQueryable of business objects (NOT the objects in my dbml file, but a translation of one of those) using an extension method (WithId(this IQueryable<BizObj> objects, guid id))  It's all set up with interfaces (IService and IRepository) for my IoC container. When I unit test the Service using a mock repository everything works fine.  When I unit test the actual repository the WithID method throws an exception.  Here are some snippets of the code I am working with:

///This is the extension method
public static IQueryable WithID(this IQueryable businessObjects, Guid postID)
{
    return from n in businessObjects
           where n.ID == postID
           select n;
}

///This is the method in my Linq to SQL Repository
public IQueryable GetNewsPosts()
{
    return from n in _context.NewsPosts
           select new Business.NewsPost(n);
}

///Same method implementation but in my Mock Repository
public IQueryable GetNewsPosts()
{
     if (this.newsList == null)
     {
        this.newsList = new List()
        {
           new NewsPost() { Body = "News Post 1", Title = "Test1", CategoryID = Guid.NewGuid() },
           new NewsPost() { Body = "News Post 2", Title = "Test2", CategoryID = Guid.NewGuid() },
           new NewsPost() { Body = "News Post 3", Title = "Test3", CategoryID = Guid.NewGuid() }
        };
    }
    return this.newsList.AsQueryable();
}

The error comes when I call everything like so:

Again, it only fails when calling the real repository.  It works fine when using the Mock Code. Any help is greatly appreciated!

Well, changing 

chris.wall:

<code>

///This is the method in my Linq to SQL Repository
public IQueryable GetNewsPosts()
{
    return from n in _context.NewsPosts
           select new Business.NewsPost(n);
}

</code>

To be

<code>

    return from n in _context.NewsPosts
           select new Business.NewsPost

            {

ID = n.ID,

Title = n.Title,

Body = n.Body

};

 </code>

It all works as expected now, I'm just not sure why it wouldn't work by passing "n" into the business object's constructor.  Any ideas?  at least I found a way to get it working..