Fluent NHibernate - 'failed to lazily initialize a collection' - Querying Over a Collection

Question

I have a self-referential model class:

public class Word
{
    public virtual int Id { get; set; }
    public virtual string Text { get; set; }
    public virtual IList<Word> Synonyms { get; set; }
    public virtual int Extra { get; set; }
}

I am trying to query for all synonyms of a word where Extra is 1 and returning the list of words in JSON format in my MVC 3 app:

[HttpPost]
public JsonResult Synonyms(string wordText)
{
    using (var session = ...)
    {
        using (var tx = session.BeginTransaction())
        {
            var word = session.QueryOver<Word>()
                              .Where(w => w.Text == wordText)
                              .SingleOrDefault();

            var results = new SynonymsResults()
            {
                Words = word.Synonyms
                            .Where(x => x.Extra == 1)
                            .Select(x => x.Text)
            };

            return Json(results);
        }

    }
}

I'm getting an error that it fails to lazily initialize the collection. I'm not sure why though, since I am still in the same session here and even using a transaction.

Answer 1

The result executes much later, after the action has finished running and outside of the session. The fact that you have returned Json(results) doesn't mean that these results will be immediately serialized into JSON. The action will first finish executing, then the ASP.NET MVC pipeline will handle the execution to the result (OnResultExecuting) and it is at this point that the JavaScriptSerializer will touch the collection. At that point of time sessions and transactions are long gone.

So either instruct your ORM to eagerly fetch the dependent collections or even better take a look at the following series of blog posts and use view models.