Hello,
for the first time ever how to compile a query with the Django ORM :/
There are two Models: The second model has a foreign key to the first model
and a type, where the combination of "first model and second model's type"
is unique. Let's say type 1 are dogs, type 2 are cats and every model1 can
only have 0 or 1 dogs and cats. I know that it could have been implemented
as two seperate tables without types and one-to-ones, but I need to query
the whole model2 often and it's implemented in this way since years.
This is not a problem for single model1 objects, since it's just a second
objects.get(...)-call as a lazy property in the model1.
But now I need a query for *all* model1-objects with two additional
columns: Has this model1 a cat, has this model1 a dog?
Here's some code (Just pseudocode - doesn't work! My actual models would be
too complicated):
class Model1(Model):
name = CharField(...)
m2types = (cats, dogs)
class Model2(Model)
m1 = ForeignKey(Model1)
type = SmallIntegerField(..., choices=m2types)
class Meta:
unique_together = ('m1', 'type')
In SQL I would do it with left outer joins:
SELECT m1.id, m1.name, c.id, d.id
FROM model1 AS m1
LEFT OUTER JOIN model2 AS c ON c.m1_id = m1.id AND c.type = 1
LEFT OUTER JOIN model2 AS d ON d.m1_id = m1.id AND d.type = 2;
So, back to my questsion: Is this possible with the Django ORM without
using raw SQL?
Note: Speed is not important. Since it is a cronjob being done half a year
and my models are just hundrets, iterating over every model1 and using the
lazy property cat and dog would be okay, and also using raw SQL would be
okay since I'm tied to PostgreSQL. I'm explicitly searching for an elegant
solution with the Django ORM.
Thanks,
Sebastian
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