Archives for: June 2010
25/06/10
Relationships in XPO
I’m replying to a post in the DevExpress XPO forum, where the question came up of how to use joins with XPO/LINQ and projection. Unfortunately, the forum system mangled my code snippets, so I thought I’d put the info up here as well.
Emilio Garcia wrote:
I trying to create a linq query to retrive some objects, this is the query:
var listadoSesiones = from u in usuariosjoin s in sesiones on u.ObjId equals s.UsuarioIdwhere s.Activa == true orderby s.FechaInicio ascending select new { u.NombreUsuario, u.NombreCompleto, s.FechaInicio, s.FechaFin };
I’m pretty sure this doesn’t have anything to do with the Guid type.
Instead, the problem is the projection you’re trying to do. Instead, you
should define your classes correctly and things should be much easier…
I’m roughly translating your names, and I’m coming up with classes that
look like this:
C#:
| public class User: XPObject { | |
| public User(Session session) : base(session) { } | |
| private string userName; | |
| public string UserName { | |
| get { return userName; } | |
| set { SetPropertyValue("UserName", ref userName, value); } | |
| } | |
| private string fullName; | |
| public string FullName { | |
| get { return fullName; } | |
| set { SetPropertyValue("FullName", ref fullName, value); } | |
| } | |
| [Association("User-Sessions")] | |
| public XPCollection Sessions { | |
| get { return GetCollection("Sessions"); } | |
| } | |
| } | |
| public class LoginSession: XPObject { | |
| public LoginSession(Session session) : base(session) { } | |
| private DateTime startTime; | |
| public DateTime StartTime { | |
| get { return startTime; } | |
| set { SetPropertyValue("StartTime", ref startTime, value); } | |
| } | |
| private DateTime endTime; | |
| public DateTime EndTime { | |
| get { return endTime; } | |
| set { SetPropertyValue("EndTime", ref endTime, value); } | |
| } | |
| private bool active; | |
| public bool Active { | |
| get { return active; } | |
| set { SetPropertyValue("Active", ref active, value); } | |
| } | |
| private User user; | |
| [Association("User-Sessions")] | |
| public User User { | |
| get { return user; } | |
| set { SetPropertyValue("User", ref user, value); } | |
| } | |
| } |
Note the two properties marked with [Association] - these are the ones
that implement the relationship for XPO. You should always set these
relationships up correctly, then it will be much easier to get to the
right data.
(As an aside - when working with legacy databases, you’ll sometimes need
to use the [Persistent(...)] attribute on properties like this to define
the name of the foreign key fields in your database.)
Once you’ve got your classes set up like this, you can easily query the
information you were looking for, utilizing these pre-configured
relationships:
C#:
| using (UnitOfWork unitOfWork = new UnitOfWork( )) { | |
| var activeSessions = | |
| from s in new XPQuery<LoginSession>(unitOfWork) | |
| where s.Active | |
| orderby s.StartTime | |
| select new { | |
| s.User.UserName, | |
| s.User.FullName, | |
| s.StartTime, | |
| s.EndTime // why this? session is active, no end time… | |
| }; | |
| foreach (var session in activeSessions) | |
| Console.WriteLine("Username: {0}, Full name: {1}, Start time: {2}", | |
| session.UserName, session.FullName, session.StartTime); | |
| } |
Of course on the other hand there’s no real need to do this either -
it’s so easy to get to the data you need through the relationship
properties, you don’t need to work with projection.
18/06/10
Training classes for DevExpress Silverlight products?
I’m thinking of a class for Silverlight components, later this year. It would probably be a two or three day class, covering the process of creating a Silverlight application with the help of the DevExpress components on that platform.
Right now I’m trying to gauge interest in the topic. If you think you might be interested in such a class sometime between October and December 2010, please let me know! I’m also interested in finding out what locations in the world would be most useful to you, so please mention that. And if you think Silverlight is a waste of your time, or mine, that’ll also be worth a mention…
Thank you for any feedback!
