RavenDB - Image Gallery Project (III) - The Application Lifecycle

The code for this and all other entries can be found here: http://github.com/robashton/RavenGallery/ 

As discussed in the previous entry, I have decided to host RavenDB within the application itself, this is a decision that lends itself very easily to the early stages of a development project against RavenDB, as there is no need to remember to run RavenDB before running the application, and it is a decision that providing you write your code properly can be changed later on in development when it becomes useful to have RavenDB running on another server or just as a separate process.

Before writing any code, we have to understand the basic components at play when communicating with RavenDB.

• IDocumentStore
  • This is the main port of call for communicating with a RavenDB server
  • This is also the main port of call for starting up a RavenDB server if running locally (DocumentStore)
  • One of these should exist per application – IE, create on start-up and persist
• IDocumentSession
  • This is created via IDocumentStore and provides interfaces for querying the document store
  • This controls the unit of work, tracks loaded documents, keeps a cache etc
  • This should be created per-unit-of-work (Typically one per HTTP request, or one per transaction)
  • NB: Whilst RavenDB supports transactions across requests, typically we avoid this and try to commit all changes once per unit of work

On start-up

So, on start-up we need to create a document store and make that available for creating document sessions when necessary (and maybe other purposes).

This is what I’ve come up with:

Bootstrapper.cs

   1:   public static class Bootstrapper

   2:      {

   3:          public static void Startup()

   4:          {

   5:              var documentStore = new EmbeddableDocumentStore

   6:              {

   7:                  Configuration = new RavenConfiguration

   8:                  {

   9:                      DataDirectory = "App_Data\\RavenDB",

  10:                  }

  11:              };

  12:              documentStore.Initialize();

  13:   

  14:              ObjectFactory.Initialize(config =>

  15:              {

  16:                  config.AddRegistry(new CoreRegistry(documentStore));

  17:              });

  18:          }

  19:      }

This is invoked from Global.asax.cs via Application_Start – we create the DocumentStore and pass it into a StructureMap registry which then sets up the container. If I wanted to switch to a different mechanism for dealing with RavenDB I could change it here and the rest of my application wouldn’t be any the wiser. I could even load the settings from a file here, but I’m not going to – so there.

Inside CoreRegistry.cs we have

   1:      public class CoreRegistry : Registry

   2:      {

   3:          public CoreRegistry(IDocumentStore documentStore)

   4:          {

   5:              For<IDocumentStore>().Use(documentStore);

   6:          }

   7:      }

Per request
Until we find a reason not to, we will create RavenDB sessions per request and secretly store them in the HttpContext.Items collection so they can be used through-out the rest of the request, of course we’ll use StructureMap to manage that for us.
CoreRegistry.cs now looks like this:

   1:  public CoreRegistry(IDocumentStore documentStore)

   2:   {

   3:    For<IDocumentStore>().Use(documentStore);

   4:    For<IDocumentSession>()

   5:       .HttpContextScoped()

   6:        .Use(x =>

   7:            {

   8:                var store = x.GetInstance<IDocumentStore>();

   9:                return store.OpenSession();

  10:            });

  11:  }

Of course this is leaking sessions because StructureMap won’t dispose of any of our created sessions unless we tell it to, so into Global.asax.cs I go once more and add the following line:

   1:          protected void Application_EndRequest()

   2:          {

   3:              ObjectFactory.ReleaseAndDisposeAllHttpScopedObjects();

   4:          }

This will do for now, I could have done this using a HttpModule or whatever I preferred, but that gets the concepts across.
In the next entry I’ll give a refresh on how documents are created/modified/queried in order to lay the groundwork for the structure of the rest of the application.

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