Peewee-async - How to do a simple JOIN (or subquery / prefetch) - python-3.x

Question

I'm stuck on a pretty simple issue with peewee-async regarding JOINs, or perhaps I need to use a subquery, or prefetch... I can't figure it out what kind of query I need to do.
I have 2 database tables (parent/child):
class Group(PeeweeModel):
id = peewee.AutoField()
name = peewee.TextField()
class Channel(PeeweeModel):
id = peewee.AutoField()
name = peewee.TextField()
group = peewee.ForeignKeyField(Group, backref="channels")
I need to fetch 1 group object, and this object has multiple channel objects.
I tried:
q = Group.select(Group, Channel).join(Channel)
But my backref 'channels' is always a ModelQuery instance, not the actual resultset.
Full code
import asyncio
import peewee
import peewee_async
from peewee_async import Manager, PooledPostgresqlDatabase
database = PooledPostgresqlDatabase('test', max_connections=4, user='postgres', password='', host='127.0.0.1')
objects = peewee_async.Manager(database)
class PeeweeModel(peewee.Model):
class Meta:
database = database
class Group(PeeweeModel):
id = peewee.AutoField()
name = peewee.TextField()
class Channel(PeeweeModel):
id = peewee.AutoField()
name = peewee.TextField()
group = peewee.ForeignKeyField(Group, backref="channels")
Group.create_table()
Channel.create_table()
database.set_allow_sync(False)
async def handler():
# create 1 group object
group = await objects.create(Group, name="TestGroup")
# create 2 channel objects, assign to group
await objects.create(Channel, name="TestName1", group=group)
await objects.create(Channel, name="TestName2", group=group)
# Query 1 group, and hopefully it will have the channels
q = Group.select(Group, Channel).join(Channel)
results = await objects.execute(q)
for result in results:
print(result.channels) # problem: Channels is not a list of channel objects, but a `ModelSelect` instead
with objects.allow_sync():
Channel.drop_table(True)
Group.drop_table(True)
loop = asyncio.get_event_loop()
loop.run_until_complete(handler())
loop.close()

Answer 1

I was able to get help from an expert™ and the solution is to use prefetch():
async def handler():
# create 1 group object
group = await objects.create(Group, name="TestGroup")
# create 2 channel objects, assign to group
await objects.create(Channel, name="TestName", group=group)
await objects.create(Channel, name="TestName", group=group)
# Query 1 group, and hopefully it will have the channels
q = Group.select(Group)
groups = await objects.prefetch(q, Channel.select(Channel))
for group in groups:
print(group, group.channels) # channels is a list of channels.
with objects.allow_sync():
Channel.drop_table(True)
Group.drop_table(True)
Peewee will figure out the relationship (backref) by itself.