nested foreach - issue with logic - asp.net-mvc

Question

This has stumped me for the last 3 hours... I'm probably just tired but can't seem to get the logic correct. Would I'd like to do is;
get a list of survey topics and a list of rated survey topics.
if none of the topics have been rated, return the first to the user to rate.
if they've all been rated, return a view saying 'yay you completed the survey'
else identify which ones have not been rated and serve those up in a view.
All topics are served up 1 at a time, each time the topic is rated, its saved then i redirect them back to this controller.
I think my string.equals is not working but can't seem to figure out why. The controller just keeps serving up the same topic. (I'm assuming its the first record that matches vs the one that doesn't?)
public ActionResult Index(string page)
{
Rating rating = new Rating();
var surveyItems = (from s in db.Surveys
where s.Category.Name.Equals(page)
select s).ToList();
var ratedItems = (from r in db.Ratings
where r.Category.Equals(page) && r.UserName.Equals(User.Identity.Name)
select r).ToList();
if (ratedItems.Count() == 0 && surveyItems.Count() > 0)
{
ViewBag.Remaining = surveyItems.Count();
rating.Topic = surveyItems.Select(si => si.Topic).FirstOrDefault();
rating.Category = page;
return View(rating);
}
else if (ratedItems.Count() > 0 && ratedItems.Count() == surveyItems.Count())
{
return View("Finished");
}
else
{
foreach (var si in surveyItems)
{
foreach (var ri in ratedItems)
{
if (!si.Topic.Equals(ri.Topic))
{
rating.Topic = si.Topic;
rating.Category = page;
ViewBag.Total = surveyItems.Count();
ViewBag.Remaining = ViewBag.Total - ratedItems.Count();
return View(rating);
}
}
}
}

Answer 1

Firstly, to answer your question directly, your inner loop will always fail because the 2 lists are not ordered AND theres no gaurantee that item 1 in each list will be the same. Even if they are, the second item from the first list will not equal the first item from the second list (inner loop).
Best bet is to tackle this entirely with LINQ, and while the query is a little difficult to read, the code is a lot cleaner.
var rating = (from s in db.Surveys
join r in db.Ratingson s.Topic equals r.Topic into rated
from ri in rated.Where(x => x.Username == User.Identity.Name).DefaultIfEmpty()
where s.Category.Name.Equals(page) && ri.Topic == null
select new RatingViewModel {Topic = s.Topic, Category = s.Category, Total = db.SurveyItems.Count(), Rated = rated.Count()}).FirstOrDefault();
if (rating == null)
{
return View("Finished");
}
return View(rating);
The LINQ query is essentially the equivalent of the following SQL (give or take)
SELECT * FROM Surveys s
LEFT OUTER JOIN Ratings r ON s.Topic = r.Topic AND r.Username = 'user'
WHERE r.Topic IS NULL
You'll also note that the query projects to RatingsViewModel, I added this because I noticed you had a few references to ViewBag as well as your Rating entity.
RatingViewModel:
public class RatingViewModel
{
public string Topic { get; set; }
public string Category { get; set; }
public int Total { get; set; }
public int Rated { get; set; }
public int Remaining {
get { return Total - Rated; }
}
}
EDIT
Played around with the query a little more, and this is the closest I could get:
// define the where's here so we can use the IQueryable multiple times in LINQ
var surveys = db.Surveys.Where(x => x.Category.Name.Equals(page));
var ratedItems = db.Ratings.Where(y => y.Username == User.Identity.Name && y.Category.Name.Equals(page));
var rated = ratedItems.Count(); // get the rated count here, otherwise we end up with an exception inside the LINQ query
var surveyTopic =
(from s in surveys
// LEFT OUTER JOIN to ratings
join r in ratedItems on s.Topic equals r.Topic into ratedSurveys
from ri in ratedSurveys.DefaultIfEmpty()
// define variables
let total = surveys.Count()
//let rated = ratedItems.Count() -- this throws a NotSupportedException... which seems odd considering the line above
// get non-rated surveys, in this case the RIGHT side of the join (Ratings) is null if there is no rating
where ri.Topic == null
// projection
select new RatingViewModel
{
Topic = s.Topic,
Category = s.Category,
Rated = rated,
Total = total
}).FirstOrDefault();
return surveyTopic == null ? View("Finished") : View(surveyTopic);
Unfortunately this results in 2 DB queries which I was hoping to avoid, still this should be a little closer to what you are after.

Answer 2

Brent,
It didn't like your solution so I tried to revamp it a bit but it's still not happy. Here's my tweak;
var surveyTopic = (from s in db.Surveys.Where(x => x.Category.Name.Equals(page))
let total = s.Topic.Count()
join r in db.Ratings.Where(y => y.UserName == User.Identity.Name) on s.Topic equals r.Topic
let rated = r.Topic.Count()
where r.Topic == null
select new RatingViewModel
{
Topic = s.Topic,
Category = s.Category.Name,
Rated = rated+1,
Total = total
}).FirstOrDefault();