message_set of Django model

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i'm new with Django and as I read the code, I don't understand the message_set attribute of Django model(called Room):

def room(request, pk):
    room = Room.objects.get(id=pk)
    **room_messages = room.message_set.all()**
    participants = room.participants.all()

portion of Models:

class Room(models.Model):
host = models.ForeignKey(User, on_delete=models.SET_NULL, null=True)
topic = models.ForeignKey(Topic, on_delete=models.SET_NULL, null=True)
name = models.CharField(max_length=200)
description = models.TextField(null=True, blank=True)
participants = models.ManyToManyField(
    User, related_name='participants', blank=True)
updated = models.DateTimeField(auto_now=True)
created = models.DateTimeField(auto_now_add=True)

class Message(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
room = models.ForeignKey(Room, on_delete=models.CASCADE)
body = models.TextField()
updated = models.DateTimeField(auto_now=True)
created = models.DateTimeField(auto_now_add=True)
model django python
1 Answers

If you define a ForeignKey from Message to Room, Django will add a relation in reverse to the from the Room model to its related Messages. By default this relation is named modelname_set with modelname the name of the origin of the model. You can specify another name by overriding the related_name=… parameter [Django-doc].

If you thus access the relation in reverse, you get all Message objects with room as there room, an equivalent query to room.message_set.all() is thus Message.objects.filter(room=room).

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