Filtering Django query filtering

Question

I'm doing some querying currently and I was wondering if I would be able to query something from these 3 models where the return would give me all the projects the users are working on. I know about the basic filtering however thats not really enough in this case, how would one go about querying through 2 foreign keys.

class User(models.Model):
    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)
    email = models.EmailField()

class ProjectUser(models.Model):
    project = models.ForeignKey("Project", on_delete=models.CASCADE)
    user = models.ForeignKey("User", on_delete=models.CASCADE)
    is_lead = models.BooleanField(default=False)

    class Meta:
        unique_together = (("project", "user"),)

class Project(models.Model):
    name = models.CharField(max_length=255)
    client = models.CharField(max_length=255)
    complete = models.BooleanField(default=False)

So you have a user and you want all the Projects that user is working on? — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jul 2, 2020 at 15:59
Yeah exactly, I wanted to get the query so then I can transform it into a JSON. — Karna
– Karna, Commented Jul 2, 2020 at 16:21

willeM_ Van Onsem · Accepted Answer · 2020-07-02 16:02:27Z

2

You can obtain the Projects a user is working on with:

Project.objects.filter(
    projectuser__user=user
)

The double underscores are used to look "through" relations. Furthermore the default related_query_name=… parameter [Django-doc] is, if not specified, the name of the model in lowercase.

answered Jul 2, 2020 at 16:02

willeM_ Van Onsem

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7 Comments

schillingt Over a year ago

You're missing the suffix _set for the default related_name.

willeM_ Van Onsem Over a year ago

@schillingt: no, the query does not use related_name, it uses related_query_name in the filtering :) The confusion comes from the fact that if you specify a related_name, and no related_query_name, then it will indeed use the related_name. But if you do not specify any of the two, it uses the name of the model in lowercase.

willeM_ Van Onsem Over a year ago

@schillingt: see docs.djangoproject.com/en/dev/ref/models/fields/… where it shows how related_query_name is used in queries, and related_name as the name of the reverse manager.

Karna Over a year ago

So for every double __ you're able to look further into the databse if the fields are connected?

willeM_ Van Onsem Over a year ago

@Karna: yes, basically you can think of __ as some sort of LEFT OUTER JOIN: dofactory.com/sql/left-outer-join

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