C# generics with linq search criteria

Question

Hello. I'm trying to make tiny helper method for simplify routine operations But on the sample:

public static int getEntityId<Type, Entity>(String name) where Entity: class
{
    Type type = _db.GetTable<Entity>().SingleOrDefault(t => t.name == name);
    return 0;
}

i get error:

Error 1 'Entity' does not contain a definition for 'name' and no extension method 'name' accepting a first argument of type 'Entity' could be found (are you missing a using directive or an assembly reference?) c:\work\asutp_migration\asutp_migration\Program.cs 89 62 asutp_migration

Actually, this is expected error, but how to solve this? All tables/classes i will use with this method have "name" field/property.

UPD 1: according to advices i did this:

public partial class unit : IHasName
{
}

interface IHasName
{
    string name { get; }
    int id { get; }
}

public static int getEntityId<Type, Entity>(String name) where Entity: class, IHasName
{
    Type type = _db.GetTable<Entity>().SingleOrDefault(t => t.name == name);
    return (type == null) ? type.id : 0;
}

and with code:

int i = getEntityId<unit>("м");
Console.WriteLine(i);

i get exception:

Unhandled Exception: System.NotSupportedException: The mapping of interface member IHasName.name is not supported.

UPD 2: http://connect.microsoft.com/VisualStudio/feedback/details/344903/linq-to-sql-mapping-interface-member-not-supported-exception i can't believe. is it related to my issue?

UPD 3: yeah, seems it's VS issue: http://social.msdn.microsoft.com/Forums/en/linqtosql/thread/bc2fbbce-eb63-4735-9b2d-26b4ab8fe589

UPD 4:

public static int getEntityId<Type>(String name) where Type: class, IHasName
{
    Type type = _db.GetTable<Type>().SingleOrDefault(t => t.name.Equals(name));
    return (type != null) ? type.id : 0;
}

so this is a solution, thank you all :-)

Answer 1

Well, you will need to make a generic constraint that specifies something more specific than class. For example, if you said where Entity : IHasName and IHasName defined a property name, then you would be all set.

Answer 2

I'll guess you're looking for something like:

public static int getEntityID<T>(string name) where T : Entity {
    T obj = _db.GetTable<T>().SingleOrDefault(t => t.name == name);
    return obj != null ? obj.id : 0;
}

here, Entity would be some base class (or interface)

public abstract class Entity { 
    public int id { get; set;}
    public string name { get; set; }
}

and your types would derive from that.

Answer 3

Going off Jimmy's post and Zerk's answer:

public static int GetEntityID<T>(string name) 
    where T : IAnimal
{
    T obj = _db.GetTable<T>().SingleOrDefault(t => t.name == name);
    return obj != null ? obj.id : 0;
}

Edit2: Since you're new to this, here's an example of the above code usage:

/* You have a LinqToSql object of type Manatee */
int manateeId = MyClass.GetEntity<Manatee>("Jack");

It sounds like you're just trying to implement a repository pattern, which totally makes things easier. Here's an example of how to do it in LinqToSql: http://aspalliance.com/1672_Implementing_the_Repository_Pattern_with_LINQtoSQL.3

Once you learn how to do this, you can modify it to use for NHibernate or ADO.NET

Edit:

public interface IAnimal
{
  string name;
}

public Manatee : IAnimal
{
  public string name {get;set;}
  public int Age {get;set;}
  public strin Weight {get;set}
}