Question

How can I achieve something like the following?

public interface IGenericRepository 
{
    int id { get; }

    T GetById<T>() where T : class
}

public class GenericRepository : IGenericRepository 
{
    //Some code here

    public T GetById<T>(int tid) where T : class 
    { 
        return from tbl in dataContext.GetTable<T> where tbl.id == tid select tbl;
    }
 }

And I would like to use this as follows:

GenericRepository gr = new GenericRepository();
Category cat = gr.GetById<Category>(15);

Of course, in this usage, tbl.id in the GenericRepository gives me an error.

SOLUTION

public class IHasId
{
    public int id { get; set; }
}

public interface IGenericRepository
{
    int id { get; }

    T GetById<T>(int id) where T : IHasId;
}

public class GenericRepository : IGenericRepository
{
    public int id
    {
        get { throw new NotImplementedException(); }
    } 

    public T GetById<T>(int id) where T : IHasId
    {
        return from tbl in dataContext.GetTable<T> where tbl.id == tid select tbl;
    }
}

And apart from these, DON’T forget to define this somewhere in your model:

public partial class Category : IHasId { }

And the usage is:

Repository rep = new Repository();
Category cat = rep.GetById<Category>(15);

Answer 1

public class IHasId
{
    public int id { get; set; }
}

public interface IGenericRepository<T>
{
    int id { get; }

    T GetById(int id);
}

public class GenericRepository<T> : IGenericRepository<T> where T : IHasId
{
    public int id
    {
        get { throw new NotImplementedException(); }
    }

    public T GetById(int id)
    {
        return from tbl in dataContext.GetTable<T> where tbl.id == tid select tbl;
    }
}