Re: Django Query to get max rating

From what I could understand, you are trying to fetch all the top ratings for each question in a group, correct?

The problem is that this query:

top_rated_list = Ratings.objects.get(rating = max_rating)

​

is returning more than one rating instance. "get" queries are supposed to return a single result, if you need more than one, you should be using a "filter" query.

This is happening because there are more than one rating with a max_rating in your database. What i think you really meant to be doing is to fetch the best for rating for a single question, so your query would look like this:

top_rated_list = Ratings.objects.get(rating = max_rating, question=i)

​

But, this can also lead to the same error when two users give a question the same rate.

In this case, if it doesn't mater if you pick one or the other, a fix for this can be:

top_rated_list = Ratings.objects.filter(rating = max_rating, question=i).first()

​

Now, the way you are doing this, the "top_rated_list" will only have one rating object everytime. To return a list of ratings, you should appending to the list:

question_top_rate =  Ratings.objects.filter(rating = max_rating, question=i).first()  top_rated_list.append(question_top_rate)  

​

Also, the way you are modelling the relationships, there is a many to many relationship from a Group to a Question, so a question belongs to multiple groups. If this is the behaviour you are looking for, you should be using a ManyToManyField as documented here:

https://docs.djangoproject.com/en/1.7/ref/models/fields/#manytomanyfield

also, take a look in the "through" parameter:

https://docs.djangoproject.com/en/1.7/ref/models/fields/#django.db.models.ManyToManyField.through

It what your really wanted was to a question belong to a single group, it would make more sense to have a ForeignKey to Group in the Question model.

You can also optimize the way you are doing the queries, but that's another topic.

--

Filipe Ximenes +55 (81) 8245-9204 Vinta Software Studio http://www.vinta.com.br

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