django - eliminating duplicate related items

Question

Here's a snippet from my application:

class PortolioItem(models.Model):
    ...
    user = models.ForeignKey(User)
    contract = models.ForeignKey(Contract)
    quantity = models.IntegerField(...)
    ...

class Contract(models.Model):
    ...
    market = models.ForeignKey(Market)
    ...

You can see that a User has the same number of PortfolioItems as the number of different contracts he owns.

I want to email users who have any "contracts" of a specific "market" in their portfolios. And I want to email a user only once, regardless of how many different types of contracts of that market he may own. Here's what I do:

#get users that want to receive notices
users = User.active_users.investment_notices_users()
#get portfolio items for a specific market
market = Market.objects.get(pk=1)
portfolio_items = PortfolioItem.objects.filter(contract__in = market.contracts.all(), user__in = users)

Since a user can have different types of contracts of the same market, the queryset may contain a user for more than once. I can eliminate duplicate users in several ways (an easy solution seems to be: queryset-->list-->set-->list), but wonder if I am at an inefficient/non-elegant solution and there can be a better ORM way that will give me a unique User queryset.

Thanks in advance.

Answer 1

If you just want the users, then the best thing is to start off with the User table:

users = User.objects.filter(portfolioitem__contract__market=market)