DB4O.cs

using Db4objects.Db4o;
using System.Linq;
using Db4objects.Db4o.Linq;
using System.Web;
using System.IO;
using System;
using System.Collections.Generic;

namespace NoSQL {

        public class Db4oSession : IDisposable, ISession {
        private IObjectContainer db;
        public IObjectContainer Container {
            get {
                return db;
            }
        }
        protected Db4oSession(IObjectServer server) {

            db= server.OpenClient();
        }

        /// <summary>
        /// Returns all T records in the repository
        /// </summary>
        public IQueryable<T> All<T>() {
            return (from T items in db
                    select items).AsQueryable();
        }

        /// <summary>
        /// Finds an item using a passed-in expression lambda
        /// </summary>
        public T Single<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression) {
            return All<T>().SingleOrDefault(expression);
        }

        /// <summary>
        /// Saves an item to the database
        /// </summary>
        /// <param name="item"></param>
        public void Save<T>(T item) {
            db.Store(item);
        }

        /// <summary>
        /// Deletes an item from the database
        /// </summary>
        /// <param name="item"></param>
        public void Delete<T>(T item) {
            db.Delete(item);
        }

        /// <summary>
        /// Deletes subset of objects
        /// </summary>
        public void Delete<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression) {
            var items = All<T>().Where(expression).ToList();
            items.ForEach(x => db.Delete(x));
        }

        /// <summary>
        /// Deletes all T objects
        /// </summary>
        public void DeleteAll<T>() {
            var items = All<T>().ToList();
            items.ForEach(x => db.Delete(x));
        }


        /// <summary>
        /// Commits changes to disk
        /// </summary>
        public void CommitChanges() {
            //commit the changes
            db.Commit();

        }
        public void Dispose() {
            //explicitly close
            db.Close();
            //dispose 'em
            db.Dispose();
        }
    }
}

Example.cs

    using (var session = NoSQL.SessionFactory.Current) {
       
        //create a category and save it
        var cat = new Category("cat 1");

        var cat2 = new Category("cat 2");

        Product p = new Product();
        p.SKU = "2354";
        p.Name = "Something peanuty";

        p.Categories.Add(cat);
        p.Categories.Add(cat2);
        
        session.Save(p);

        session.CommitChanges();
    }

ISession.cs

using System;
namespace NoSQL {
    public interface ISession:IDisposable {
        void CommitChanges();
        Db4objects.Db4o.IObjectContainer Container { get; }
        void Delete<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression);
        void Delete<T>(T item);
        void DeleteAll<T>();
        void Dispose();
        T Single<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression);
        System.Linq.IQueryable<T> All<T>();
        void Save<T>(T item);
    }
}

SessionFactory.cs

using Db4objects.Db4o;
using System.Linq;
using Db4objects.Db4o.Linq;
using System.Web;
using System.IO;
using System;
using System.Collections.Generic;

namespace NoSQL { 

   public class SessionFactory {
        static ISession _current;
        //this needs to stay static - can't have more than 
        //one server on the file
        static IObjectServer _server;

        public static ISession CreateSession() {

            if (_server == null) {
                string _dbPath = System.Configuration.ConfigurationManager
                    .ConnectionStrings["ObjectStore"].ConnectionString;

                //check to see if this is pointing to data directory
                //change as you need btw
                if (_dbPath.Contains("|DataDirectory|")) {

                    //we know, then, that this is a web project
                    //and HttpContext is hopefully not null...

                    _dbPath = _dbPath.Replace("|DataDirectory|", "");
                    string appDir = HttpContext.Current.Server.MapPath("~/App_Data/");
                    _dbPath = Path.Combine(appDir, _dbPath);
                }
                _server = Db4oFactory.OpenServer(_dbPath, 0);
            }

            return new Db4oSession(_server);
        }

        public static Db4oSession Current {
            get {
                if (_current == null)
                    _current = CreateSession();
                return (Db4oSession)_current;
            }
        }
    }
}