如何编写Django ORM查询，其中选择表与另一个表共享公共列？

Question

I'm using Django and Python 3.7. I have these two models. Note they both have a similar field

class Article(models.Model):
    publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE,)


class WebPageStat(models.Model):
    objects = WebPageStatManager()
    publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE, )
    score = models.BigIntegerField(default=0)

I would like to write a Django ORM query that selects one of the models but does a join on the shared column in order to do a comparison on the "score" field. I tried the below, but alas the error

Article.objects.filter(publisher=webpagestat.publisher, webpagestat.score__gte==100)
  File "<input>", line 1
SyntaxError: positional argument follows keyword argument

How do I include the "WebPageStat" table in my join?

Answer 1

What you want is easily done in Django by using lookups that span relations . In your example you need to add a way of referencing the related objects in the ORM. This is donde by setting the related_name attribute of the ForeignKey fields. Although this is not strictly necessary it is more clear in this way. You can read more about related_name and related_query_name here . In short, your models should look like:

class Article(models.Model):
    publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE, related_name='articles')


class WebPageStat(models.Model):
    objects = WebPageStatManager()
    publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE, related_name='stats')
    score = models.BigIntegerField(default=0)

Once this is done your query will be carried out by the following code:

Article.objects.filter(publisher__stats__score__gte=100)

What this query is doing in short is selecting every article whose publisher has at least one web page stat whose score is greater than or equal to 100.