Skip to main content

Digging through SignalR - Dependency Resolver

I’m continuing the series of post related to SignalR with dependency injection.
When having a complicated business you can start to group different functionalities in classes. Because of this you can end up very easily with classes that accept in constructor 4-5 or even 10 parameters.
public abstract class PersistentConnection
{
    public PersistentConnection(
        IMessageBus messageBus, IJsonSerializer jsonSerializer, 
        ITraceManager traceManager, IPerformanceCounterManager performanceCounterManager,
        IAckHandler ackHandler, IProtectedData protectedData, 
        IConfigurationManager configurationManager, ITransportManager transportManager,
        IServerCommandHandler serverCommandHandler, HostContext hostContext)
    {
            
    }
    ...
}
Of course you have a decoupled solution that can be tested very easily, but in the same time you have a fat constructor.
People would say: “Well, we have dependency injector, the resolver will handle the constructor and resolve all the dependencies”. This is true, the resolver will inject all the dependencies automatically.
In general, because you don’t want to have a direct dependency to a specific dependency injector stack, people tend to create a wrapper over dependency resolver. The same thing was done in SignalR also.
public interface IDependencyResolver : IDisposable
{
    object GetService(Type serviceType);
    IEnumerable<object> GetServices(Type serviceType);
    void Register(Type serviceType, Func<object> activator);
    void Register(Type serviceType, IEnumerable<Func<object>> activators);
}
Additionally, they done something more. In ctor, they don’t send all the dependencies that are already register in the IoC container. They send directly the dependency resolver, which will be used by the class itself to resolve all the external dependencies.
public abstract class PersistentConnection
{
    public PersistentConnection(IDependencyResolver resolver, HostContext hostContext)
    {
        Initialize(resolver, hostContext);
    }

    public virtual void Initialize(IDependencyResolver resolver, HostContext context)
    {
        ...
        MessageBus = resolver.Resolve<IMessageBus>();
        JsonSerializer = resolver.Resolve<IJsonSerializer>();
        TraceManager = resolver.Resolve<ITraceManager>();
        Counters = resolver.Resolve<IPerformanceCounterManager>();
        AckHandler = resolver.Resolve<IAckHandler>();
        ProtectedData = resolver.Resolve<IProtectedData>();

        _configurationManager = resolver.Resolve<IConfigurationManager>();
        _transportManager = resolver.Resolve<ITransportManager>();
        _serverMessageHandler = resolver.Resolve<IServerCommandHandler>();
        ...
    }

    ...
}
It is important to notify that you don’t need to inject everything through the resolver. You can have specific dependencies injected directly by constructor. For example, HostContext is something specific for each connection. Because of this is more natural to send this context using the constructor. Is something variable that is changing from one connection to another.
Why is the best approach to this problem?
It cannot say that one is better than another. Using this solution, the constructor itself will be lighter, but in the same time you add dependency to the resolver. In a perfect world you shouldn’t have constructors with 7-10 parameters… but when you have cases like this, this solution could be pretty interesting.

Comments

Popular posts from this blog

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

Run native .NET application in Docker (.NET Framework 4.6.2)

Scope
The main scope of this post is to see how we can run a legacy application written in .NET Framework in Docker.

Context
First of all, let’s define what is a legacy application in our context. By a legacy application we understand an application that runs .NET Framework 3.5 or higher in a production environment where we don’t have any more the people or documentation that would help us to understand what is happening behind the scene.
In this scenarios, you might want to migrate the current solution from a standard environment to Docker. There are many advantages for such a migration, like:

Continuous DeploymentTestingIsolationSecurity at container levelVersioning ControlEnvironment Standardization
Until now, we didn’t had the possibility to run a .NET application in Docker. With .NET Core, there was support for .NET Core in Docker, but migration from a full .NET framework to .NET Core can be costly and even impossible. Not only because of lack of features, but also because once you…