how to pass parameters on resolve time in autofac

Question

I write following register type in autofac:

 builder.RegisterType<NoteBookContext>()
        .As<DbContext>()
        .WithParameter(ResolvedParameter.ForNamed<DbContext>("connectionstring"));

In fact I write this code for injecting NoteBookContext with a connectionstring parameter. (ie : new NoteBookContext(string connectionstring))

Now , How can I Pass value of parameter at runtime?

Answer 1

The WithParameter method has a overload that accept delegate for dynamic instanciation.

The first argument is a predicate selecting the parameter to set whereas the second is the argument value provider :

builder.RegisterType<NoteBookContext>()
       .As<DbContext>()
       .WithParameter((pi, c) => pi.Name == "connectionstring", 
                      (pi, c) => c.Resolve<IConnectionStringProvider>().ConnectionString);

See Passing Parameters to Register from Autofac documentation for more detail.

Answer 2

In order to pass the connection string value while resolving, we first need to pass the delegate of the constructor into the Register method, and then pass the value of connection string with the NamedParameter into the Resolve method.

For example:

ContainerBuilder builder = new ContainerBuilder();

builder.Register((pi, c) => new NoteBookContext(pi.Named<string>("connectionstring")))
            .As<DbContext>();

Now, on resolve time, we can assign to the resolved DBContext the conncetionstring value of Consts.MyConnectionString:

IContainer container = builder.Build();

NoteBookContext noteBookContext = container.Resolve<DbContext>(
    new NamedParameter(
        "connectionstring", Consts.MyConnectionString
    )
);