How can I join three Django Models to return a queryset? - django

Question

I want to create a queryset that references three related models, and allows me to filter. The SQL might look like this:
SELECT th.id, th.customer, ft.filename, fva.path
FROM TransactionHistory th
LEFT JOIN FileTrack ft
ON th.InboundFileTrackID = ft.id
LEFT JOIN FileViewArchive fva
ON fva.FileTrackId = ft.id
WHERE th.customer = 'ACME, Inc.'
-- AND ft.filename like '%storage%' --currently don't need to do this, but seeing placeholder logic would be nice
I have three models in Django, shown below. It's a bit tricky, because the TransactionHistory model has two foreign keys to the same model (FileTrack). And FileViewArchive has a foreign key to FileTrack.
class FileTrack(models.Model):
id = models.BigIntegerField(db_column="id", primary_key=True)
filename = models.CharField(db_column="filename", max_length=128)
class Meta:
managed = False
db_table = "FileTrack"
class TransactionHistory(models.Model):
id = models.BigIntegerField(db_column="id", primary_key=True)
customer = models.CharField(db_column="Customer", max_length=128)
inbound_file_track = models.ForeignKey(
FileTrack,
db_column="InboundFileTrackId",
related_name="inbound_file_track_id",
on_delete=models.DO_NOTHING,
null=True,
)
outbound_file_track = models.ForeignKey(
FileTrack,
db_column="OutboundFileTrackId",
related_name="outbound_file_track_id",
on_delete=models.DO_NOTHING,
null=True,
)
class Meta:
managed = False
db_table = "TransactionHistory"
class FileViewArchive(models.Model):
id = models.BigIntegerField(db_column="id", primary_key=True)
file_track = models.ForeignKey(
FileTrack,
db_column="FileTrackId",
related_name="file_track_id",
on_delete=models.DO_NOTHING,
null=True,
)
path = models.CharField(db_column="Path", max_length=256)
class Meta:
managed = False
db_table = "FileViewArchive"
One thing I tried:
qs1 = TransactionHistory.objects.select_related('inbound_file_track').filter(customer='ACME, Inc.')
qs2 = FileViewArchive.objects.select_related('file_track').all()
qs = qs1 & qs2 # doesn't work b/c they are different base models
And this idea to use chain doesn't work either because it's sending two separate queries an I'm not altogether sure if/how it's merging them. I'm looking for a single query in order to be more performant. Also it returns an iterable, so I'm not sure I can use this in my view (Django Rest Framework). Lastly x below returns a TransactionHistory object, so I can't even access the fields from the other two models.
from itertools import chain
c = chain(qs1 | qs2) # great that his this lazy and doesn't evaluate until used!
type(c) # this returns <class 'itertools.chain'> and it doesn't consolidate
x = list(c)[0] # runs two separate queries
type(x) # a TransactionHistory object -> so no access to the Filetrack or FileViewArchive fields
Any ideas how I can join three models together? Something like this?:
qs = TransactionHistory.objects.select_related('inbound_file_track').select_related('file_track').filter(customer='ACME, Inc.', file_track__filename__contains='storage')
More info: this is part of a view that will look like below. It returns a querysets that is used as part of a Django Rest Framework view.
class Transaction(generics.ListAPIView):
serializer_class = TransactionSerializer
def filter_queryset(self, queryset):
query_params = self.request.query_params.copy()
company = query_params.pop("company", [])[0]
filename = query_params.pop("filename", [])[0]
# need code here that generate filtered queryset for filename and company
# qs = TransactionHistory.objects.select_related('inbound_file_track').select_related('file_track').filter(customer='ACME, Inc.', file_track__filename__contains='storage')
return qs.order_by("id")

Answer 1

Based from the sql query you shared, you are filtering based on the inbound_file_track file name. So something like this should work:
TransactionHistory.objects.select_related(
'inbound_file_track',
).prefetch_related(
'inbound_file_track__file_track_id',
).filter(
customer='ACME, Inc.', inbound_file_track___filename__contains='storage',
)