EDIT: Why DataReader opened error occurs in this map? [duplicate]

Question

I'm trying to pass a map to a view. Before that I populate it with data from some entities(Session, Movie, Theater). I start doing a selection in my sessions:

var sessions = from s in db.Sessions where s.TheaterID == id orderby s.MovieID, s.Time select s;

This is the method. Inside it I iterate over each session and verify if in my map I have a list with the movie name as a key. When execution reaches thie very point I'm receiving the infamous "There is already an open DataReader associated with this Command which must be closed first." exception. I can't cast to a list because of types:

public ActionResult MyAction(int id) { Theather theater = db.Theater.Find(id); ViewBag.TheaterName = theater.NomeCinema; var sessions = from s in db.Sessions where s.TheaterID == id orderby s.MovieID, s.Time select s; var mapMovies = new Dictionary<string, List<DateTime>>(); foreach (Session s in sessions) { if ( !mapMovies.ContainsKey( s.Movie.MovieName ) ) { mapMovies.Add( s.Movie.MovieName, new List<DateTime>() ); } mapMovies[s.Movie.MovieName].Add(s.Time); } ViewBag.MapMovies = mapMovies; return View(); }

The error occurs in this line:

if ( !mapMovies.ContainsKey( s.Movie.MovieName ) )

What do I need to do to pass this error?

In which line you get the exception?

Gusman
– Gusman

2017-07-28 02:47:45 +00:00
Commented Jul 28, 2017 at 2:47 — Gusman
– Gusman, Commented Jul 28, 2017 at 2:47
@Gusman Sorry, I forgot to put this. Inserting now.

learner
– learner

2017-07-28 02:51:03 +00:00
Commented Jul 28, 2017 at 2:51 — learner
– learner, Commented Jul 28, 2017 at 2:51

Gusman · Accepted Answer · 2017-07-28 02:57:42Z

You are using lazy load, so when you execute if ( !mapMovies.ContainsKey( s.Movie.MovieName ) ) the context tries to issue another query to retrieve the movie, but as you are in the middle of an enumeration (which holds a datareader open) you get the exception.

There are two solutions:

1-Materialize the query converting the result to a list:

var sessions = (from s in db.Sessions where s.TheaterID == id orderby s.MovieID, s.Time select s).ToList();

2-Include the Movie entity on the query so it does eager load instead of lazy load:

var sessions = from s in db.Sessions.Include(s => s.Movie) where s.TheaterID == id orderby s.MovieID, s.Time select s;

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