Global ObjectContext or local one?

I'm starting with the Entity Framework and the repository pattern. I'm confused about the ObjectContext. Is it better to instantiate it each time we need it? I'm using like that:

        private GenericRepository _genericRepository;

        public EmployeeDAO()
        {
            var _context = new NorthwindEntities();
            this._genericRepository = 开发者_开发知识库new GenericRepository(_context);
        }

        public Employee FindByID(int employeeID)
        {
            Employee _employee = this._genericRepository.Single<Employee>(x => x.EmployeeID == employeeID );
            return _employee;
        }

Not sure what exactly you mean by Global, but a singleton ObjectContext is not a good idea. The ObjectContext is a Unit of work, and should be pretty much short lived. The exact implementation details may depend on what kind of application you are developing. E.g. for a web application it is quite common to have one ObjectContext instance per web request.

You can also check out similar questions here:

Entity Framework 4 ObjectContext Lifetime

EF - and repository pattern - multiple contexts