Architecture abstraction problem in Repository ASP.NET MVC - asp.net-mvc

Question

I'm working with MVC ASP.NET 3.5 SP1 on VS2008.
I'm looking for a way to abstract this three methods I have in my Users repository.
public User GetUser(Log log)
{
return db.Users.FirstOrDefault(u => u.Logs.Any(l => l.id.Equals(log.id)));
}
public User GetUser(Product product)
{
return db.Users.FirstOrDefault(u => u.Products.Any(pr => pr.id.Equals(product.id)));
}
public User GetUser(Photo photo)
{
return db.Users.FirstOrDefault(u => u.Photos.Any(ph => ph.id.Equals(photo.id)));
}
My DB.edmx contains the models
User [id, username, ...]
Product [id, name, ...]
Photo [id, name, ...]
Log [id, data, ...]
Is it possible to have only ONE method for all of these (and future) methods based upon model.id search?

Answer 1

public User GetUser(Expression<Func<User, bool>> restriction)
{
return db.Users.Where(restriction).FirstOrDefault();
}
Now use it:
var u = Repository.GetUser(u => u.Logs.Any(l => l.id.Equals(log.id)));
You can also use MS DynamicQuery:
using System.Linq.Dynamic;
//...
public User GetUser(string propertyName, int id)
{
var restriction = propertyName + ".Any(id = #0)";
return db.Users.Where(restriction, id).FirstOrDefault();
}
var u = Repository.GetUser("Logs", log.id);
I may not have the syntax quite correct, but you get the idea.

Answer 2

If all the associated entities (Log, Product and Photo) will be searched by a common property (id INT) then maybe you could try something like this...
First, create an interface:
public interface IUserAssociation
{
int id { get; }
}
Then each of the three classes would implement this interface like so:
public partial class Product : IUserAssociation
{
}
The the GetUser method would look like so:
public User GetUser<T>(T entity) where T : IUserAssociation
{
var type = typeof(T);
if (type == typeof(Log))
{
return db.Users.FirstOrDefault(u => u.Logs.Any(l => l.id.Equals(entity.id)));
}
else if (type == typeof(Product))
{
return db.Users.FirstOrDefault(u => u.Products.Any(pr => pr.id.Equals(entity.id)));
}
else if (type == typeof(Photo))
{
return db.Users.FirstOrDefault(u => u.Photos.Any(ph => ph.id.Equals(entity.id)));
}
else
{
throw new ArgumentException();
}
}
Then you should be able to call GetUser and pass it a Log, Photo or Product entity from one method. It is not very elegant but would work for this specific situation.

Answer 3

I like Craig's solution better but I'd suggest this:
Repository.GetUser(u => u.Logs, log);
Which will be possible if all your entities derive from
public interface IEntity { public int Id { get; } }
Then method will be like
public User GetUser<T, Y>(Func<T, IList<Y>> getlist, Y sample)
where T: IEntity
where Y: IEntity
{
return db.Users.Select(x => getlist(x).Any(y => y.Id == sample.Id)).FirstOrDefault();
}
Also if we take idea of S#arp Architecture that if entity1.Id == entity2.Id (for persistent entities) then Equals(entity1, entity2) - we can use getlist(x).Contains(sample).