Question

edit #2: Question solved halfways. Look below

As a follow-up question, does anyone know of a non-intrusive way to solve what i’m trying to do below (namely, linking objects to each other without triggering infinite loops)?

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I try to create a asp.net-mvc web application, and get a StackOverFlowException. A controller triggers the following command:

    public ActionResult ShowCountry(int id)     {         Country country = _gameService.GetCountry(id);         return View(country);     } 

The GameService handles it like this (WithCountryId is an extension):

    public Country GetCountry(int id)     {         return _gameRepository.GetCountries().WithCountryId(id).SingleOrDefault();     } 

The GameRepository handles it like this:

    public IQueryable<Country> GetCountries()     {         var countries =  from c in _db.Countries                select new Country                {                    Id = c.Id,                    Name = c.Name,                    ShortDescription = c.ShortDescription,                    FlagImage = c.FlagImage,                    Game = GetGames().Where(g => g.Id == c.GameId).SingleOrDefault(),                    SubRegion = GetSubRegions().Where(sr => sr.Id == c.SubRegionId).SingleOrDefault(),                };         return countries;     } 

The GetGames() method causes the StackOverflowException:

    public IQueryable<Game> GetGames()     {         var games = from g in _db.Games                                   select new Game                {                    Id = g.Id,                    Name = g.Name                 };         return games;      } 

My Business objects are different from the linq2sql classes, that’s why I fill them with a select new.

An unhandled exception of type ‘System.StackOverflowException’ occurred in mscorlib.dll

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edit #1: I have found the culprit, it’s the following method, it triggers the GetCountries() method which in return triggers the GetSubRegions() again, ad nauseam:

    public IQueryable<SubRegion> GetSubRegions()     {         return from sr in _db.SubRegions                select new SubRegion                {                    Id = sr.Id,                    Name = sr.Name,                    ShortDescription = sr.ShortDescription,                    Game = GetGames().Where(g => g.Id == sr.GameId).SingleOrDefault(),                    Region = GetRegions().Where(r => r.Id == sr.RegionId).SingleOrDefault(),                    Countries = new LazyList<Country>(GetCountries().Where(c => c.SubRegion.Id == sr.Id))                };     } 

Might have to think of something else here 🙂 That’s what happens when you think in an OO mindset because of too much coffee

Answer 1

The problem might be this: countries have subregions and subregions have countries. I don’t know how you implement the lazy list, but that might keep calling GetCountries and then GetSubRegions and so on. To find that out, I would launch the debugger en set breakpoints on the GetCountries and GetSubRegions method headers.

I tried similar patterns with LinqToSql, but it’s hard to make bidirectional navigation work without affecting the performance to much. That’s one of the reasons I’m using NHibernate right now.