Creating GrainId

[jbockle]

I'm creating a library where I want the consumer to choose what the primary key type is - I see I can use GrainId for this, is there a better way of instiating one? I'm doing the following currently:

public interface IMyLibraryGrain : IGrain
{
    Task Foo();
}

// and user can create a a GrainId using an extension method something like below..
public static GrainId CreateMyLibraryGrainId(this IGrainFactory grainFactory, Guid|long|string key)
{
    return grainFactory.GetGrain(typeof(IMyLibraryGrain), key).GetGrainId();
}

[ReubenBond]

I'm not entirely sure what you're after, but perhaps I can supply a bit of detail:

A GrainId consists of two components, Type and Key, both are essentially strings.
Orleans treats the Key component as opaque.
The Type components has some meaning because it maps to grain implementation classes and if those classes are generic then the Type component will contain the encoded generic parameters (eg, my-grain`2[[int],[string]]).

Orleans.Runtime.GrainIdKeyExtensions is a static class with methods for creating Guid & long keys (encoded as strings)
You can use this to create Guid/long keys. For string keys, you can pass the string directly to GrainId.Create(...). These keys have no special meaning to Orleans - they're just strings.

The trickier part is the grain type. If you know what the name of the grain type you need is (eg, because it's using the default convention-based grain type where UserGrain => user, or because you put a [GrainType("user-profile")] attribute on the grain class), you can pass that as a string. Otherwise, you have to do a 2-step dance:

• Take your TInterface and resolve the corresponding GrainInterfaceType (also a string: the encoded name of the interface)
• Take your GrainInterfaceType and resolve the default GrainType which implements it (you can override the default by putting [DefaultGrainType("user-profile")] on the grain interface). To do this, you can use GrainInterfaceTypeToGrainTypeResolver.

Both of these types can be injected. So, a GrainId creator class might look like this:

public class GrainIdFactory
{
    private readonly GrainInterfaceTypeResolver _grainInterfaceTypeResolver;
    private readonly GrainInterfaceTypeToGrainTypeResolver _grainInterfaceTypeToGrainTypeResolver;

    public GrainIdFactory(
        GrainInterfaceTypeResolver interfaceTypeResolver,
        GrainInterfaceTypeToGrainTypeResolver interfaceToTypeResolver)
    {
        _grainInterfaceTypeResolver = interfaceTypeResolver;
        _grainInterfaceTypeToGrainTypeResolver = interfaceToTypeResolver;
    }

    public GrainId CreateGrainId<TInterface>(Guid grainKey) where TInterface : IAddressable
    {
        GrainType grainType = ResolveGrainType(typeof(TInterface));
        GrainId grainId = GrainId.Create(grainType, GrainIdKeyExtensions.CreateGuidKey(grainKey));
        return grainId;
    }

    public GrainId CreateGrainId<TInterface>(long grainKey) where TInterface : IAddressable
    {
        GrainType grainType = ResolveGrainType(typeof(TInterface));
        GrainId grainId = GrainId.Create(grainType, GrainIdKeyExtensions.CreateIntegerKey(grainKey));
        return grainId;
    }

    public GrainId CreateGrainId<TInterface>(string grainKey) where TInterface : IAddressable
    {
        GrainType grainType = ResolveGrainType(typeof(TInterface));
        GrainId grainId = GrainId.Create(grainType, grainKey);
        return grainId;
    }

    private GrainType ResolveGrainType(Type interfaceType)
    {
        GrainInterfaceType grainInterfaceType = _grainInterfaceTypeResolver.GetGrainInterfaceType(interfaceType);
        GrainType grainType = _grainInterfaceTypeToGrainTypeResolver.GetGrainType(grainInterfaceType);
        return grainType;
    }
}

One important thing to note: the mapping from GrainInterfaceType to GrainType is reliant on the silo being started, since it needs to build up that mapping. In the case of a client, it relies on the client being connected to the cluster, since it needs to fetch the mapping from the cluster (the type which does this is IClusterManifestProvider).

Hope that helps.

[jbockle]

thanks for the info