Question

I m trying migrating an existing web application to use RavenDB.

I currently have pages in my web application which allow you to view Categories, SubCategories and Resources based on an id in the querystring.

However I notice that RavenDB generates ids for aggregate roots, but not for child entities.

I don t think subcategory is an aggregate root (a Category has SubCategories), so am making it a sub-document of my Category document.

Am I wrong to make it a sub-document as I m accessing it directly by its id passed in on the querystring? But if not, how should I access individual SubCategories as RavenDB does not seem to generate ids for entities that are not aggregate roots?

Answer 1

There s a long but interesting discussion over on the Raven mailing list about this exact situation.

The short answer is that Raven isn t designed to do this, only root entities get an id, everything else is treated as a value type. But you can implement it yourself, see the code sample at the end of the thread for info.

Answer 2

I ran into this problem but wasn t comfortable with letting the documents generate the ID s as I didn t feel it was thread safe, particularly for web based environments.

Eventually I decided to let the server generate the id s for me using a the GenerateDocumentKey method like so:

using (var session = Store.OpenSession())
{
    if(category.SubCategories != null)
    {
       var newSubCategories = data.BankAccounts.Where(x => string.IsNullOrEmpty(x.Id));
        foreach (var sc in newSubCategories)
            sc.Id = session.Advanced.Conventions.GenerateDocumentKey(sc);    
    }

    session.Store(data);
    session.SaveChanges();
}

This way I m allowing the database to generate the child Id s and can ensure that I won t have to cater for race conditions etc in the actual class itself.

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