Question

In POCO, I am using explicit Loading via LoadProperty to load the data. I need to filter and sort the data from the property that’s loaded and return the main object.

Say, there is an album class of which photos is a collection. I need to return the “album” object from the DAL. So, the code would be

public Album GetPhotos()
    {
        using (var context = new Entities())
        {
            //....code for loading album....
            context.LoadProperty(album, "Photos");
            //I need to return ONLY the latest 10 photos
            // album.Photos = album.Photos.OrderByDescending(a=>a.CreateDate).Take(10); //DOES NOT WORK
            return album;
        }
    }

Now in the above code, I need to return only latest 10 photos, I cannot filter or sort the photos collection as shown in the code. What’s the best way to handle this? Even if we create a new object, how would we copy all the album information to the new album?

Answer 1

Like it’s mentioned, if you want to have any sort of customized navigation property loading (e.g. filtering or ordering) then you cannot use the built in explicit eager/deferred loading methods (e.g. Load). Since you are using POCOs, you only have 2 options to go for:

Filtered Projection with Anonymous Types:

var album = context.Albums.Where(a => a.AlbumId == 1).Select(a => new  
{
    a,
    Photos = a.Photos.OrderByDescending(alb => alb.CreateDate).Take(10)
});

This will returns an anonymous type Which might not always be desirable, in that case there is yet another way:

Two Tracked Queries:

Album album = context.Albums.Where(a => a.AlbumId == 1).Single();
List<Photo> photos = context.Photos
                            .Where(p => p.AlbumId == 1)
                            .OrderByDescending(a => a.CreateDate).Take(10)
                            .ToList();

foreach (Photo photo in photos)
{
    album.Photos.Add(photo);
}