When is the best time to load lookup tables using prism/unity?

Question

I am looking for some advice on a good design for loading lookup tables such as state codes using Prism Unity? My view libraries are domain focused and I have modules that pass in an IUnityContainer. In the initialize section I register with the container the RegisterType such as IStateCode, StateCode.

Should I registerType, then load the state object and then use RegisterInstance? Should this be done in each domain (dll) or should I centrally load the tables once, and where? I thought about loading the lookup tables in the Load of the mainwindow, but I would have to reference all of the lookup classes in that module. If I use a central location to load the lookup tables, I don't have to worry about lookup tables being null and it's located in one area. How say yee?

Answer 1

The approach that I have taken with this sort of thing is to create a central project in the solution; that could be called Core.UI (or whatever you like). There, I create a class that I register with the container as a singleton, which loads the data it needs at application start up (via the Initialize call; see code). This is commonly referred to as a service.

You could make when the data is loaded as flexible as you like. At application load time, or the first time the property is accessed. I do mine up front, since the data is not huge, and it doesn't change that often. You may even want to consider some sort of caching mechanism here, too.

I have done something similar for products, too. Below is for US state codes.

public class StateListService : IStateListService // The interface to pass around
{
    IServiceFactory _service_factory;
    const string country = "United States";
    public StateListService(IServiceFactory service_factory)
    {
        _service_factory = service_factory;
        Initialize();
    }

    private void Initialize()
    {
        // I am using WCF services for data
        // Get my WCF client from service factory
        var address_service = _service_factory.CreateClient<IAddressService>();
        using (address_service)
        {
            try
            {
                // Fetch the data I need
                var prod_list = address_service.GetStateListByCountry(country);
                StateList = prod_list;
            }
            catch
            {
                StateList = new List<AddressPostal>();
            }
        }
    }

    // Access the data from this property when needed
    public List<AddressPostal> StateList { get; private set; }
}

EDIT:

To register the above as a singleton in Prism 6, add this line of code to the method you use to initialize your container. Usually in the bootstapper.

RegisterTypeIfMissing(typeof(IStateListService), typeof(StateListService), true);