Include nested entities using LINQ

Question

I'm messing around with LINQ for the first time, and I'm using EF 4.1 code first.

I have entities containing nested Lists of other entities, for example:

class Release
{
    int ReleaseID { get; set; }
    string Title { get; set; }
    ICollection<OriginalTrack> OriginalTracks { get; set; }
}

class OriginalTrack
{
    int OriginalTrackID { get; set; }
    string Title { get; set; }
    ICollection<Release> Releases { get; set; }
    ICollection<OriginalArtist> OriginalArtists { get; set; }
}

class OriginalArtist
{
    int OriginalArtistID { get; set; }
    string Name { get; set; }
    ICollection<OriginalTrack> OriginalTracks { get; set; }
}

I'm wondering what is the quickest way, in one LINQ query, to obtain all the information for where ReleaseID == some value.

I've done my homework, but have found solutions that require implicit rebuilding of an object (usually anonymous) with the required data. I want the data out of the database in the exact format that it is held within the database, i.e. pulling a Release object with relevant ReleaseID pulls and populates all the OriginalTrack and OriginalArtist data in the Lists.

I know about Include(), but am not sure how to apply it for multiple entities.

All help greatly appreciated.

Answer 1

Use Include. This is the purpose of Include, and there's no reason to write a bunch of nested select statements.

context.Releases.Include("OriginalTracks.OriginalArtist")
    .Where(release => release.ReleaseID == id);

This is simpler to write, simpler to read, and preserves your existing data structure.

To use Include you need to specify the name of the property you want to return - this means the name as it exists in your code, not in the database. For example:

• .Include("OriginalTracks") will include the OriginalTracks property on each Release
• .Include("OriginalTracks.OriginalArtist") will include OriginalTracks property on each Release, and the OriginalArtist on each Track (note that it's not possible - syntactically or logically - to include an OriginalArtist within including the OriginalTrack)
• .Include("OriginalTracks").Include("OtherProperty") will include the OriginalTracks and OtherProperty objects on each Release.

You can chain as many of these as you like, for example:

.Include("Tracks.Artist").Include("AnotherProperty")
    .Include("ThirdProperty.SomeItems").Where(r => r.something);

is perfectly valid. The only requirement is that you put the Include on the EntitySet, not on a query - you can't .Where().Include().

Answer 2

Don't worry about using include here

just do something like the following

var query = 
    from release in ctx.Releases
    select new {
        release,
        originalTracks = from track in release.OriginalTracks
                         select new {
                               track,
                               releases = track.Releases,
                               orignialArtist = from artist in track.OriginalArtists
                                                select new {
                                                     artist,
                                                     artist.OriginalTracks
                                                }
                         }
        }

var Releases = query.Select(x => x.Release);

Should load all of your data

I worked with information from this post here.

http://blogs.msdn.com/b/alexj/archive/2009/10/13/tip-37-how-to-do-a-conditional-include.aspx

Answer 3

To include the nested entities without using string literals, use Select, like this:

context.Releases.Include(r => r.OriginalTracks.Select(t => t.OriginalArtist))
    .Where(release => release.ReleaseID == id);