Dependency Injection / Singleton in RIA Domain Service

Many a times there are requirement to share a value/property between multiple Domain Service calls. Problem is on each call we have new instance of the DomainService. i.e. Each time a client calls into the DomainService endpoint, the RIA hosting layer uses the singleton DomainService.Factory to create a new instance of the requested DomainService type. The default IDomainServiceFactory implementation expects a DomainService type to provide a parameter-less constructor. So there is no possibility of injecting the shared property during the creation of Domain Service. In my case scenario was to share a unique instance of the following to multiple Domain Service call –

SerializationService and  SunixAuthService
 

See below the approach –

1.      Created my own custom DomainServiceFactory -

public class SunixDomainServiceProvider : IDomainServiceFactory

{

        private SerializationService _serializationService;

        private SunixAuthService _sunixAuthService;

        public SunixDomainServiceProvider()

        {

            _serializationService = new SerializationService();

            _sunixAuthService = new SunixAuthService();

        }

        public DomainService CreateDomainService(Type domainServiceType, DomainServiceContext context)

        {

            DomainService domainService;

            if (typeof(CustomDomainService) == domainServiceType)

            {

                domainService = new CustomDomainService(_serializationService, _sunixAuthService);

            }

            else

            {

                domainService = (DomainService)Activator.CreateInstance(domainServiceType);

            }

            domainService.Initialize(context);

            return domainService;

        }

        public void ReleaseDomainService(DomainService domainService)

        {

            domainService.Dispose();

        }

}

2. Registed the Factory in the Global.asax

Now that we have a custom factory, we’ll have to make sure it gets used to instantiate our DomainService. The easiest way to do this is to add a Global.asax file to our web site and bootstrap the factory there.

protected void Application_Start(object sender, EventArgs e)

{

    DomainService.Factory = new SunixDomainServiceProvider();

}

3. Now change your DomainService ctor to accept these values –

[EnableClientAccess()]

public class CustomDomainService : LinqToEntitiesDomainService<EntityTestDBEntities>

{

        public CustomDomainService(ISerializationService sss, ISunixAuthService acs)

        {

           

        }

        public IQueryable<School> GetSchools()

        {

            return this.ObjectContext.Schools;

        }

}

Now if you Test the Service you find the constructor of the SunixDomainServiceProvider is hitting only once irrespective of how many calls clients are making. 

        public SunixDomainServiceProvider()

        {

            _serializationService = new SerializationService();

            _sunixAuthService = new SunixAuthService();

        }

Conclusion: If you want to maintain a instance of some property/value then the CustomDomainServicePactory is appropriate place and can’t be achieved at the DomainService itself.