How to make a query on related_name field?

Question

I have to models connected by a ForeignKey

class User(AbstractUser):
   ...

and

class PrivateMessage(models.Model):
    user_from = models.ForeignKey(
        User,
        verbose_name=u'From',
        related_name='sent_messages',
    )
    user_to = models.ForeignKey(
        User,
        verbose_name=u'To',
        related_name='received_messages',
    )

Is there any way to get all the addresses for a particular user. For example, if

u = User.objects.get(id=1)
messages = PrivateMessage.objects.filter(user_from=u)
for m in messages:
    users.add(m.user_to)

How to obtain a list of users that appear in user_to for these messages using only Django ORM methods?

Answer 1

I think a better idea would be to define ManyToManyField on the User model:

class User(AbstractUser):
    #...
    receivers = models.ManyToManyField('self', through='Message',
                                      symmetrical=False, related_name="senders")

class Message(models.Model):
    user_from = models.ForeignKey(MyUser, related_name='messages_from')
    user_to = models.ForeignKey(MyUser, related_name='messages_to')
    message = models.CharField(max_length=100, default="")
    #...

Then to retrieve users list on the other end you simply do:

User.objects.get(id=1).receivers.all()  # who I sent the message to
User.objects.get(id=1).senders.all()    # who sent me a message

This way you have a nice clear API.