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