I am trying to run some code on objects that are loaded from RavenDB, and I need to do it just after the object has been loaded with its property values.
I've tried intercepting the deserialization process using a CustomCreationConverter and overriding ReadJson, but the object I can access at that point has all the properties set, except the one I need : the Id. Is there somewhere else I can slot into the pipeline in order to do this?
The reason you don't see the Id is because it's not part of the document, it's in the metadata as #id.
If you want to intercept client side, you can register a custom Conversion Listener. Create a class that implements IDocumentConversionListener and register it with documentStore.RegisterListener(). In the DocumentToEntity method, you can run your custom logic. The documentation is lacking on Listeners in general, but there is another topic that also uses them:
http://ravendb.net/kb/16/using-optimistic-concurrency-in-real-world-scenarios
The other option would be to add a bundle that intercepts on the server side. For that, you would use a Read Trigger.
Related
So, I have a viewmodel class in a xamarin project that I inject some dependencies into via ninject binding on app start. One of these is an IDialogService.
When my MainPage in my application changes it raises a property changed event and I rebind the implementation of the dialog service since it is tied to the MainPage.
If my viewmodel has already been created with lets say DialogServiceA and then when MainPage changes we rebind to DialogServiceB, will my viewmodel be using service A or B? I think it is using A and therefore does not display in the UI because it is tied to a MainPage that no longer exists.
So, if this is the case how can I dynamically change my dialog service but then update classes that have already been instantiated without changing everything to get the current dialog service from the container every time its used (therefore not injecting it at all really, and doing more of a servicelocator)
Also, if this approach is completely wrong, set me straight.
You're right. Re-configuration of the container does not affect already instanciated objects.
If you want to change dependencies without re-instanciating the dependent (parent ViewModel) there's a few possibilities for you:
use a factory to instanciate the service every time. Implement an Abstract Factory (Site by Mark Seeman) or use Ninject.Extensions.Factory to do so
instead of injecting a service directly, inject an adapter. The adapter then redirects the request to the currently appropriate service. To do so, either all service can be injected into the adapter, or you can use a factory as with the possibility above.
instead of inject a service directly, inject a proxy. The proxy is quite similar to the adapter, but instead of coding every method / property redirection specifically, you code a generic redirect by an interceptor. Here's a tutorial on castle dynamic proxy
At the end of the day, however, i believe you'll also need a way to manage when to change the service / which it should be. There's probably a design alternative which doesn't rely on exchanging objects in such a manner.. which would make it an easier (and thus better?) design.
Edit: i just saw that you also tagged the question as xamarin-forms. In that case it most likely won't be an option to use either a dynamic proxy nor ninject.extensions.factory (it relies on dynamic proxies, too). Why? dynamic proxy / IL emitting is not supported on all platforms, AFAIR specifically on Apple devices this can't be done.
I am using the NamedScoped Ninject extension in an attempt to create object graphs that are constructed everytime a command handler is constructed by the container. In other words, I want a fresh object graph for every command that might get processed by its corresponding handler.
I have used the .DefinesNamedScope("TopLevelOrhcestrator") binding when registering my "command handlers" as they are the top level for command processing.
A type in this named scope needs to be injected with the result of a method call on a type already registered in this named scope. I thought the best way to do this would be with a ninject provider.
Inside the provider I attempt to resolve the type in hopes I can call a method on it to pass into another object I am creating within this named scope. The problem I'm having is that when I ask the IContext for the instance inside the customer provider I get an exception that says "No matching scopes are available, and the type is declared InNamedScope(TopLevelOrchestrator).
context.Kernel.Get<TypeAlreadyRegisteredInScope>().MethodThatGetsAnotherDependency()
Is it possible to get types from the container inside a Ninject provider when they are registered inside a named scope?
EDIT
I apologize if the use case seems a bit odd, I am experimenting with some ideas about how to manage my units of work and other services/managers that may need a handle to the uow to complete a business usecase. I know its common for the unit of work to be "started" and then passed into all dependencies that may need to take part in a larger process. I was thinking I'd rather let my orchestrator take a unit of work factory so that it could deterministically destroy the UOW and it would be clear who the owner of a usecase is. What would get supplied to the managers/services would be a proxy to the unit of work that would be null until a real unit of work was started by the orchestrator. That's why I was attempting to link the proxy from the already registered type in my provider. This is all very experimental at this point and was testing some ideas.
I'd be happy to hear any further thoughts.
For MethodThatGetsAnotherDependency() to be able to .Get<>() an instance that is bound .InNamedScope(...) you will need to add the Context Preservation Extension.
This is because NamedScope is adding a parameter to the request context of the binding that has .DefinesNamedScope(...). As soon as that request is over, that context and it's parameters are forgotten. Now with the ContextPreservation extension the context is kept and reused for late / factory creations (Func<>, interface factory with .ToFactory() binding...). It think it should also work with providers.
If not, just switch to a factory instead of a provider.
However i have to admit that i don't fully understand why/what you are trying to achieve. There might be simpler ways.
I have a WCF service application (actually, it uses WCF Web API preview 5) that intercepts each request and extracts several header values passed from the client. The idea is that the 'interceptor' will extract these values and setup a ClientContext object that is then globally available within the application for the duration of the request. The server is stateless, so the context is per-call.
My problem is that the application uses IoC (Unity) for dependency injection so there is no use of singleton's, etc. Any class that needs to use the context receives it via DI.
So, how do I 'dynamically' create a new context object for each request and make sure that it is used by the container for the duration of that request? I also need to be sure that it is completely thread-safe in that each request is truly using the correct instance.
UPDATE
So I realize as I look into the suggestions below that part of my problem is encapsulation. The idea is that the interface used for the context (IClientContext) contains only read-only properties so that the rest of the application code doesn't have the ability to make changes. (And in a team development environment, if the code allows it, someone will inevitably do it.)
As a result, in my message handler that intercepts the request, I can get an instance of the type implementing the interface from the container but I can't make use of it. I still want to only expose a read-only interface to all other code but need a way to set the property values. Any ideas?
I'm considering implementing two interfaces, one that provides read-only access and one that allows me to initialize the instance. Or casting the resolved object to a type that allows me to set the values. Unfortunately, this isn't fool-proof either but unless someone has a better idea, it might be the best I can do.
Read Andrew Oakley's Blog on WCF specific lifetime managers. He creates a UnityOperationContextLifetimeManager:
we came up with the idea to build a Unity lifetime manager tied to
WCF's OperationContext. That way, our container objects would live
only for the lifetime of the request...
Configure your context class with that lifetime manager and then just resolve it. It should give you an "operation singleton".
Sounds like you need a Unity LifetimeManager. See this SO question or this MSDN article.
I am interested in the best practice of the following scenario. I have a CustomAction method that hits a web service and returns some information that I use to populate a combo box. Later in the install process in another CustomAction method, I need to access some of the meta data returned from that first web service call.
In the first method, I create a List that is a public static member of my CustomAction class. In my second method when I access the list its empty.
My thoughts were to serialize it using xaml serialization into a session variable then deserialize it in my second method.
Am I way off here? Is there a better way?
I will assume that your second custom action is making configuration changes to the machine and running in the execute sequence as deferred with no impersonation. This means it can only access the CustomActionData property.
This means your first custom action will have to serialize the CustomActionData property for the second one to deserialize. Now the CustomActionData is a Key:Value collection and what you do with it ( including have a Key with a Value that is yet another serialized datatype ) is completely up to you.
Be sure to read the DTF documentation to understand how to use the CustomActionData type and members off the Session class to your advantage.
If I have an object that holds the parameters for my method. I need to change the Object to have an additional property. I have full control over the server, but not over all of the clients. Will this change make those clients break?
I am using a self-hosted service with a binary endpoint.
I am new to WCF so my apologies if this is a silly question.
I guess you are asking about a class that represents your DataContract.
Learn about DataContract versioning and how various changes in your DataContract affect the compatibility in MSDN
In short the answer is No, it will not break the client code. The serialized graph of the data contract will deserialize to the available data members matching by their names and assigned through the property setter method. Obviously in this case, your newly added data member will not have value. Since you have full control on the server side code, you just have to make sure this newly added member need to be dealt in such a way that it is meaningful in the new implementation and allow for default/unassigned value.