Web API, Light Inject and Passing a Static Dictionary to the data layer

Question

We have a multi-database solution and are passing the connection string to a factory function like so:

container.Register<IDbContextFactory>(
    f => new DynamicDbContextFactory(ClientConfig.GetConnectionString()),
    new PerScopeLifetime());

ClientConfig contains a static dictionary that gets populated on app start that maps a sub domain to a connection string. It seems that this approach is causing a memory leak (not 100% sure about this causing the leak but there is a leak).

public class ClientConfig
{
    private static ConcurrentDictionary<string, string> ConnectionStringManager 
    { 
        get;
        set; 
    }

    // etc.
}

My question is in MVC what is the best way to hold a list of connection strings that can be easily looked up on each request in order to pass that down the chain.

Answer 1

Edit : The question was initially tagged with Autofac

---

With Autofac you don't have to use a dictionary and something like that to do what you want. You can use a custom parameter :

public class ConnectionStringParameter : Parameter
{
    public override Boolean CanSupplyValue(ParameterInfo pi, 
                                           IComponentContext context, 
                                           out Func<Object> valueProvider)
    {
        valueProvider = null;

        if (pi.ParameterType == typeof(String)
            && String.Equals(pi.Name, "connectionString", 
                             StringComparison.OrdinalIgnoreCase))
        {
            valueProvider = () =>
            {
                // get connectionstring based on HttpContext.Current.Request.Url.Host 
                return String.Empty;
            };
        }

        return valueProvider != null;
    }
}

Then register your Parameter using a Module

public class ConnectionStringModule : Autofac.Module
{
    protected override void AttachToComponentRegistration(
        IComponentRegistry componentRegistry, IComponentRegistration registration)
    {
        registration.Preparing += registration_Preparing;
    }

    private void registration_Preparing(Object sender, PreparingEventArgs e)
    {
        Parameter[] parameters = new Parameter[] { new ConnectionStringParameter() }; 
        e.Parameters = e.Parameters.Concat(parameters);
    }
}

Module you have to register inside your container using

ContainerBuilder builder = new ContainerBuilder();
builder.RegisterModule(new ConnectionStringModule());

Each time Autofac have to resolve a parameter of type String named connectionString it will used the custom parameter and get your connectionstring based on what you want.

---

By the way this code sample use HttpContext.Current. In case of a multithreaded process it may return null. I don't recommend using HttpContext.Current for such things. You can use an intermediate class instead of accessing it, for example a IConnectionstringProvider interface.

public interface IConnectionstringProvider
{
    String ConnectionString { get; }
}
public class ConnectionStringProvider : IConnectionstringProvider
{
    public ConnectionStringProvider(Strong host)
    {
        // get connectionstring based on host
        this._connectionString = String.Empty;
    }

    private readonly String _connectionString;

    public String ConnectionString
    {
        get { return this._connectionString; }
    }
}

Inside your Parameter you will have to change the valueProvider by

valueProvider = () =>
{
    return context.Resolve<IConnectionstringProvider>().ConnectionString; 
};

And finally you will have to register your IConnectionstringProvider at the beginning of the request lifetimescope :

class Program
{
    static void Main(string[] args)
    {
        ContainerBuilder builder = new ContainerBuilder();
        builder.RegisterModule(new ConnectionStringModule());

        IContainer container = builder.Build();
        container.ChildLifetimeScopeBeginning += container_ChildLifetimeScopeBeginning;
    }

    private static void container_ChildLifetimeScopeBeginning(
        Object sender, LifetimeScopeBeginningEventArgs e)
    {
        String host = HttpContext.Current.Request.Url.Host; 
        ContainerBuilder childLifetimeScopeBuilder = new ContainerBuilder();
        childLifetimeScopeBuilder.RegisterInstance(new ConnectionStringProvider(host))
                                 .As<IConnectionstringProvider>()
                                 .SingleInstance();
        childLifetimeScopeBuilder.Update(e.LifetimeScope.ComponentRegistry);
    }
}

Of course there is many way to do it but you have the idea