Attention to the NoSQL movement is growing within the Microsoft .NET Framework community as we continue to hear of companies sharing their implementation experiences of it in applications that we know and use. With this heightened awareness comes the curiosity to dig in and identify how a NoSQL data store could provide benefits or other potential solutions to the software that developers are currently crafting. But where do you start, and how hard is the learning curve? Maybe an even more relevant concern: How much time and effort are required to fire up a new data storage solution and start writing code against it? After all, you have the setup process of SQL Server for a new application down to a science, right?
Word has reached the .NET community on the wings of a raven about a new option for a NoSQL-type data-layer implementation. RavenDB (
ravendb.net) is a document database designed for the .NET/Windows platform, packaged with everything you need to start working with a nonrelational data store. RavenDB stores documents as schema-less JSON. A RESTful API exists for direct interaction with the data store, but the real advantage lies within the .NET client API that comes bundled with the install. It implements the Unit of Work pattern and leverages LINQ syntax to work with documents and queries. If you’ve worked with an object-relational mapper (ORM)—such as the Entity Framework (EF) or NHibernate—or consumed a WCF Data Service, you’ll feel right at home with the API architecture for working with documents in RavenDB.
The learning curve for getting up and running with an instance of RavenDB is short and sweet. In fact, the piece that may require the most planning is the licensing strategy (but even that’s minimal). RavenDB offers an open source license for projects that are also open source, but a commercial license is required for closed source commercial projects. Details of the license and the pricing can be found at ravendb.net/licensing. The site states that free licensing is available for startup companies or those looking to use it in a noncommercial, closed source project. Either way, it’s worthwhile to quickly review the options to understand the long-term implementation potential before any prototyping or sandbox development.
RavenDB Embedded and MVC
RavenDB can be run in three different modes:
- As a Windows service
- As an IIS application
- Embedded in a .NET application
The first two have a fairly simple setup process, but come with some implementation strategy overhead. The third option, embedded, is extremely easy to get up and running. In fact, there’s a NuGet package available for it. A call to the following command in the Package Manager Console in Visual Studio 2010 (or a search for the term “ravendb” in the Manage NuGet Packages dialog) will deliver all of the references needed to start working with the embedded version of RavenDB:
Install-Package RavenDB-Embedded
Details of the package can be found on the NuGet gallery site at
bit.ly/ns64W1.
Adding the embedded version of RavenDB to an ASP.NET MVC 3 application is as simple as adding the package via NuGet and giving the data store files a directory location. Because ASP.NET applications have a known data directory in the framework named App_Data, and most hosting companies provide read/write access to that directory with little or no configuration required, it’s a good place to store the data files. When RavenDB creates its file storage, it builds a handful of directories and files in the directory path provided to it. It won’t create a top-level directory to store everything. Knowing that, it’s worthwhile to add the ASP.NET folder named App_Data via the Project context menu in Visual Studio 2010 and then create a subdirectory in the App_Data directory for the RavenDB data (see
Figure 1).
.png "App_Data Directory Structure")
Figure 1 App_Data Directory Structure
A document data store is schema-less by nature, hence there’s no need to create an instance of a database or set up any tables. Once the first call to initialize the data store is made in code, the files required to maintain the data state will be created.
Working with the RavenDB Client API to interface with the data store requires an instance of an object that implements the Raven.Client.IDocumentStore interface to be created and initialized. The API has two classes, DocumentStore and EmbeddedDocumentStore, that implement the interface and can be used depending on the mode in which RavenDB is running. There should only be one instance per data store during the lifecycle of an application. I can create a class to manage a single connection to my document store that will let me access the instance of the IDocumentStore object via a static property and have a static method to initialize the instance (see
Figure 2).
Figure 2 Class for DocumentStore
public class DataDocumentStore
{
private static IDocumentStore instance;
public static IDocumentStore Instance
{
get
{
if(instance == null)
throw new InvalidOperationException(
"IDocumentStore has not been initialized.");
return instance;
}
}
public static IDocumentStore Initialize()
{
instance = new EmbeddableDocumentStore { ConnectionStringName = "RavenDB" };
instance.Conventions.IdentityPartsSeparator = "-";
instance.Initialize();
return instance;
}
}
The static property getter checks a private static backing field for a null object and, if null, it throws an InvalidOperationException. I throw an exception here, rather than calling the Initialize method, to keep the code thread-safe. If the Instance property were allowed to make that call and the application relied upon referencing the property to do the initialization, then there would be a chance that more than one user could hit the application at the same time, resulting in simultaneous calls to the Initialize method. Within the Initialize method logic, I create a new instance of the Raven.Client.Embedded.EmbeddableDocumentStore and set the ConnectionStringName property to the name of a connection string that was added to the web.config file by the install of the RavenDB NuGet package. In the web.config, I set the value of the connection string to a syntax that RavenDB understands in order to configure it to use the embedded local version of the data store. I also map the file directory to the Database directory I created in the App_Data directory of the MVC project:
<connectionStrings>
<add name="RavenDB " connectionString="DataDir = ~\App_Data\Database" />
</connectionStrings>
The IDocumentStore interface contains all of the methods for working with the data store. I return and store the EmbeddableDocumentStore object as an instance of the interface type IDocumentStore so I have the flexibility of changing the instantiation of the EmbeddedDocumentStore object to the server version (DocumentStore) if I want to move away from the embedded version. This way, all of my logic code that will handle my document object management will be decoupled from the knowledge of the mode in which RavenDB is running.
RavenDB will create document ID keys in a REST-like format by default. An “Item” object would get a key in the format “items/104.” The object model name is converted to lowercase and is pluralized, and a unique tracking identity number is appended after a forward slash with each new document creation. This can be problematic in an MVC application, as the forward slash will cause a new route parameter to be parsed. The RavenDB Client API provides a way to change the forward slash by setting the IdentityPartsSeparator value. In my DataDocumentStore.Initialize method, I’m setting the IdentityPartsSeparator value to a dash before I call the Initialize method on the EmbeddableDocumentStore object, to avoid the routing issue.
Adding a call to the DataDocumentStore.Initialize static method from the Application_Start method in the Global.asax.cs file of my MVC application will establish the IDocumentStore instance at the first run of the application, which looks like this:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
DataDocumentStore.Initialize();
}
From here I can make use of the IDocumentStore object with a static call to the DataDocumentStore.Instance property to work on document objects from my embedded data store within my MVC application.
RavenDB Objects
To get a better understanding of RavenDB in action, I’ll create a prototype application to store and manage bookmarks. RavenDB is designed to work with Plain Old CLR Objects (POCOs), so there’s no need to add property attributes to guide serialization. Creating a class to represent a bookmark is pretty straightforward.
Figure 3 shows the Bookmark class.
Figure 3 Bookmark Class
public class Bookmark
{
public string Id { get; set; }
public string Title { get; set; }
public string Url { get; set; }
public string Description { get; set; }
public List<string> Tags { get; set; }
public DateTime DateCreated { get; set; }
public Bookmark()
{
this.Tags = new List<string>();
}
}
RavenDB will serialize the object data into a JSON structure when it goes to store the document. The well-known “Id” named property will be used to handle the document ID key. RavenDB will create that value—provided the Id property is empty or null when making the call to create the new document—and will store it in a @metadata element for the document (which is used to handle the document key at the data-store level). When requesting a document, the RavenDB Client API code will set the document ID key to the Id property when it loads the document object.
The JSON serialization of a sample Bookmark document is represented in the following structure:
{
"Title": "The RavenDB site",
"Url": "http://www.ravendb.net",
"Description": "A test bookmark",
"Tags": ["mvc","ravendb"],
"DateCreated": "2011-08-04T00:50:40.3207693Z"
}
The Bookmark class is primed to work well with the document store, but the Tags property is going to pose a challenge in the UI layer. I’d like to let the user enter a list of tags separated by commas in a single text box input field and have the MVC model binder map all of the data fields without any logic code seeping into my views or controller actions. I can tackle this by using a custom model binder for mapping a form field named “TagsAsString” to the Bookmark.Tags field. First, I create the custom model binder class (see
Figure 4).
Figure 4 BookmarkModelBinder.cs
public class BookmarkModelBinder : DefaultModelBinder
{
protected override void OnModelUpdated(ControllerContext controllerContext,
ModelBindingContext bindingContext)
{
var form = controllerContext.HttpContext.Request.Form;
var tagsAsString = form["TagsAsString"];
var bookmark = bindingContext.Model as Bookmark;
bookmark.Tags = string.IsNullOrEmpty(tagsAsString)
? new List<string>()
: tagsAsString.Split(',').Select(i => i.Trim()).ToList();
}
}
Then I update the Globals.asax.cs file to add the BookmarkModelBinder to the model binders at application startup:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
ModelBinders.Binders.Add(typeof(Bookmark), new BookmarkModelBinder());
DataDocumentStore.Initialize();
}
To handle populating an HTML text box with the current tags in the model, I’ll add an extension method to convert a List<string> object to a comma-separated string:
public static string ToCommaSeparatedString(this List<string> list)
{
return list == null ? string.Empty : string.Join(", ", list);
}
Unit of Work
The RavenDB Client API is based on the Unit of Work pattern. To work on documents from the document store, a new session needs to be opened; work needs to be done and saved; and the session needs to close. The session handles change tracking and operates in a manner that’s similar to a data context in the EF. Here’s an example of creating a new document:
using (var session = documentStore.OpenSession())
{
session.Store(bookmark);
session.SaveChanges();
}
It’s optimal to have the session live throughout the HTTP request so it can track changes, use the first-level cache and so on. I’ll create a base controller that will use the DocumentDataStore.Instance to open a new session on
action executing, and on
action executed will save changes and then dispose of the session object (see
Figure 5). This allows me to do all of the work desired during the execution of my action code with a single open session instance.
Figure 5 BaseDocumentStoreController
public class BaseDocumentStoreController : Controller
{
public IDocumentSession DocumentSession { get; set; }
protected override void OnActionExecuting(ActionExecutingContext filterContext)
{
if (filterContext.IsChildAction)
return;
this.DocumentSession = DataDocumentStore.Instance.OpenSession();
base.OnActionExecuting(filterContext);
}
protected override void OnActionExecuted(ActionExecutedContext filterContext)
{
if (filterContext.IsChildAction)
return;
if (this.DocumentSession != null && filterContext.Exception == null)
this.DocumentSession.SaveChanges();
this.DocumentSession.Dispose();
base.OnActionExecuted(filterContext);
}
}
MVC Controller and View Implementation
The BookmarksController actions will work directly with the IDocumentSession object from the base class and manage all of the Create, Read, Update and Delete (CRUD) operations for the documents.
Figure 6 shows the code for the bookmarks controller.
Figure 6 BookmarksController Class
public class BookmarksController : BaseDocumentStoreController
{
public ViewResult Index()
{
var model = this.DocumentSession.Query<Bookmark>()
.OrderByDescending(i => i.DateCreated)
.ToList();
return View(model);
}
public ViewResult Details(string id)
{
var model = this.DocumentSession.Load<Bookmark>(id);
return View(model);
}
public ActionResult Create()
{
var model = new Bookmark();
return View(model);
}
[HttpPost]
public ActionResult Create(Bookmark bookmark)
{
bookmark.DateCreated = DateTime.UtcNow;
this.DocumentSession.Store(bookmark);
return RedirectToAction("Index");
}
public ActionResult Edit(string id)
{
var model = this.DocumentSession.Load<Bookmark>(id);
return View(model);
}
[HttpPost]
public ActionResult Edit(Bookmark bookmark)
{
this.DocumentSession.Store(bookmark);
return RedirectToAction("Index");
}
public ActionResult Delete(string id)
{
var model = this.DocumentSession.Load<Bookmark>(id);
return View(model);
}
[HttpPost, ActionName("Delete")]
public ActionResult DeleteConfirmed(string id)
{
this.DocumentSession.Advanced.DatabaseCommands.Delete(id, null);
return RedirectToAction("Index");
}
}
The IDocumentSession.Query<T> method in the Index action returns a result object that implements the IEnumerable interface, so I can use the OrderByDescending LINQ expression to sort the items and call the ToList method to capture the data to my return object. The IDocumentSession.Load method in the Details action takes in a document ID key value and de-serializes the matching document to an object of type Bookmark.
The Create method with the HttpPost verb attribute sets the CreateDate property on the bookmark item and calls the IDocumentSession.Store method off of the session object to add a new document record to the document store. The Update method with the HttpPost verb can call the IDocumentSession.Store method as well, because the Bookmark object will have the Id value already set. RavenDB will recognize that Id and update the existing document with the matching key instead of creating a new one. The DeleteConfirmed action calls a Delete method off of the IDocumentSession.Advanced.DatabaseCommands object, which provides a way to delete a document by key without having to load the object first. I don’t need to call the IDocumentSession.SaveChanges method from within any of these actions, because I have the base controller making that call on
action executed.
All of the views are pretty straightforward. They can be strongly typed to the Bookmark class in the Create, Edit and Delete markups, and to a list of bookmarks in the Index markup. Each view can directly reference the model properties for display and input fields. The one place where I’ll need to vary on object property reference is with the input field for the tags. I’ll use the ToCommaSeparatedString extension method in the Create and Edit views with the following code:
@Html.TextBox("TagsAsString", Model.Tags.ToCommaSeparatedString())
This will allow the user to input and edit the tags associated with the bookmark in a comma-delimited format within a single text box.
Searching Objects
With all of my CRUD operations in place, I can turn my attention to adding one last bit of functionality: the ability to filter the bookmark list by tags. In addition to implementing the IEnumerable interface, the return object from the IDocumentSession.Query method also implements the IOrderedQueryable and IQueryable interfaces from the .NET Framework. This allows me to use LINQ to filter and sort my queries. For example, here’s a query of the bookmarks created in the past five days:
var bookmarks = session.Query<Bookmark>()
.Where( i=> i.DateCreated >= DateTime.UtcNow.AddDays(-5))
.OrderByDescending(i => i.DateCreated)
.ToList();
Here’s one to page through the full list of bookmarks:
var bookmarks = session.Query<Bookmark>()
.OrderByDescending(i => i.DateCreated)
.Skip(pageCount * (pageNumber – 1))
.Take(pageCount)
.ToList();
RavenDB will build dynamic indexes based on the execution of these queries that will persist for “some amount of time” before being disposed of. When a similar query is rerun with the same parameter structure, the temporary dynamic index will be used. If the index is used enough within a given period, the index will be made permanent. These will persist beyond the application lifecycle.
I can add the following action method to my BookmarksController class to handle getting bookmarks by tag:
public ViewResult Tag(string tag)
{
var model = new BookmarksByTagViewModel { Tag = tag };
model.Bookmarks = this.DocumentSession.Query<Bookmark>()
.Where(i => i.Tags.Any(t => t == tag))
.OrderByDescending(i => i.DateCreated)
.ToList();
return View(model);
}
I expect this action to be hit on a regular basis by users of my application. If that’s indeed the case, this dynamic query will get turned into a permanent index by RavenDB with no additional work needed on my part.
A Raven Sent to Awaken Us
With the emergence of RavenDB, the .NET community appears to finally have a NoSQL document store-type solution catered toward it, allowing Microsoft-centric shops and developers to glide through the nonrelational world that so many other frameworks and languages have been navigating for the past few years. Nevermore shall we hear the cries of a lack of nonrelational love for the Microsoft stack. RavenDB is making it easy for .NET developers to start playing and prototyping with a nonrelational data store by bundling the install with a clean client API that mimics data-management techniques that developers are already employing. While the perennial argument between relational and nonrelational surely won’t die out, the ease of trying out something “new” should help lead to a better understanding of how and where a nonrelational solution can fit within an application architecture.
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