What is the unit of work pattern in EF?

Question

I am learning EF and have seen many examples, and during my learning I came to know about using repository and unit of work patterns. I got why to use repository but I do not have understanding of unit of work really is.

Having no understanding is making DAL understanding difficult. Kindly guide me.

Thanks

Answer 1

The DataContext or ObjectContext is the Unit of Work.

So, your DAL will save, delete and retrieve objects and your DataContext/ObjectContext will keep track of your objects, manage transactions and apply changes.

This is an example just to illustrate the idea of the solution.

using(var context = new ObjectContext()) { // Unit of Work     var repo = new ProductRepository(context);     var product = repo.GetXXXXXXX(...);     ...      // Do whatever tracking you want to do with the object context. For instance:     // if( error == false) {      //     context.DetectChanges();     //     context.SaveChanges(SaveOptions.AcceptAllChangesAfterSave);     // } } 

And your repository will look like:

public abstract class Repository {      public Respository(ObjectContext context){         CurrentContext = context;     }      protected ObjectContext CurrentContext { get; private set; }  }  public class ProductRespository : Repository {     public ProductRespository(ObjectContext context) : base(context){     }      public Product GetXXXXXX(...){         return CurrentContext... ; //Do something with the context     } }     

Another way is to put the unit of work (Object context) globally:

You need to define what will be your unit of work scope. For this example, it will be a web request. In a real world implementation, I'd use dependency injection for that.

public static class ContextProvider {      public static ObjectContext CurrentContext {         get { return HttpContext.Items["CurrentObjectContext"];     }      public static void OpenNew(){         var context = new ObjectContext();         HttpContext.Items["CurrentObjectContext"] = context;      }      public static void CloseCurrent(){         var context = CurrentContext;         HttpContext.Items["CurrentObjectContext"] = null;         // Do whatever tracking you want to do with the object context. For instance:         // if( error == false) {          //     context.DetectChanges();         //     context.SaveChanges(SaveOptions.AcceptAllChangesAfterSave);         // }         context.Dispose();     } } 

In this example, ObjectContext is the unit of work and it will live in the current request. In your global asax you could add:

protected void Application_BeginRequest(object sender, EventArgs e){     ContextProvider.OpenNew(); }  protected void Application_EndRequest(object sender, EventArgs e){     ContextProvider.CloseCurrent(); } 

In your Repositories, you just call ContextProvider.CurrentContext