CODEWITHSUNDEEP
pythondjango
AARON DARDIK
AARON DARDIK

Reputation: 15

How can I construct a Django model whose fields are dependent upon another model's fields

I currently am making a simple newspaper Django application, and am working on the Articles model which looks as follows:

class Article(models.Model):
    title = models.CharField(max_length=255)
    body = models.TextField()
    #date = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey(
        get_user_model(),
        on_delete=models.CASCADE, 
    )
    topic = models.CharField(max_length=255)
    score_choices = [(-5,'-5'), (-4, '-4'), (-3,'-3'), (-2, '-2'), (-1,'-1'), 
    (0,'0'),(1,'1'), (2,'2'), (3,'3'), (4,'4'), (5,'5')]
    score = models.IntegerField(choices=score_choices, default=0)

I am attempting to create another model that looks something like this:

class Topic(models.Model):
    topic_name = models.CharField(max_length=255)
    average_score =

Within the topic model, what I would like to do is somehow query all the Articles that have topic_name as their topic, and then return a list of scores that have been entered for Articles with that topic.

I'm currently pretty lost on this issue and I'm not even sure anymore if using the Django models is the best route. I've been reading through the Django Documentation as well as Third-Party books for a while but I can't find any reference here.

To summarize, I have two models: Article and Topic. Article has a field called 'topic' as well and I would like to create a field for my Topic class that is a function of the score field for all Article objects whose 'topic' field agrees with that of my separate Topic class. I apologize if this is confusing and I don't know all the terminology as I am trying to teach myself.

I have read through Django Documentation's pages on Models, Queries, Many-to-Many Relationships and various other properties. I still am unsure as to the solution.

Upvotes: 0

Views: 93

Answers (1)

user2390182
user2390182

Reputation: 73470

Something like the following would work, using aggregation:

from django.db.models.aggregates import Avg

class Topic(models.Model):
    topic_name = models.CharField(max_length=255)

    def average_score(self):
        return Article.objects.filter(topic=self.topic_name).aggregate(avg=Avg('score')).get('avg')

Upvotes: 1

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