Hello,
i have just upgraded to Django 3.2 to use nested FilteredRelation, but i
have noticed strange behaviors, this is the code:
/from django.db.models import FilteredRelation, Q//
//from django.db import models//
//
//
/
///class A(models.Model):/
/// foo = models.IntegerField()/
//
///class B(models.Model):/
/// value = models.IntegerField()/
//
///class C(models.Model):/
/// a = models.ForeignKey('A', on_delete=models.CASCADE)/
/// b = models.ForeignKey('B', on_delete=models.CASCADE)/
/////
//>>> qs = A.objects.annotate(bla=FilteredRelation('c',
condition=Q(c__b__value=1))).select_related('bla')//
//>>> str(qs.query)//
//'SELECT "base_a"."id", "base_a"."foo", bla."id", bla."a_id",
bla."b_id" FROM "base_a" LEFT OUTER JOIN "base_c" bla ON ("base_a"."id"
= bla."a_id" AND ("base_b"."value" = 1))'/
_*PROBLEM 1:*_
It is not joining the model B. As you can see on the query there is
"base_b" without the join.
_*PROBLEM 2:*_
There is another strange behavior, if i "execute" the queryset i get this:
/>>> qs//
//Traceback (most recent call last)://
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/backends/utils.py",
line 84, in _execute//
// return self.cursor.execute(sql, params)//
//psycopg2.errors.UndefinedTable: ERRORE: elemento FROM per la tabella
"t4" mancante//
//LINE 1: ... "base_c" bla ON ("base_a"."id" = bla."a_id" AND
(T4."value"...//
//^//
//
//The above exception was the direct cause of the following exception://
//
//Traceback (most recent call last)://
// File "<console>", line 1, in <module>//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/models/query.py",
line 256, in __repr__//
// data = list(self[:REPR_OUTPUT_SIZE + 1])//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/models/query.py",
line 262, in __len__//
// self._fetch_all()//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/models/query.py",
line 1324, in _fetch_all//
// self._result_cache = list(self._iterable_class(self))//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/models/query.py",
line 51, in __iter__//
// results = compiler.execute_sql(chunked_fetch=self.chunked_fetch,
chunk_size=self.chunk_size)//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/models/sql/compiler.py",
line 1169, in execute_sql//
// cursor.execute(sql, params)//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/backends/utils.py",
line 98, in execute//
// return super().execute(sql, params)//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/backends/utils.py",
line 66, in execute//
// return self._execute_with_wrappers(sql, params, many=False,
executor=self._execute)//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/backends/utils.py",
line 75, in _execute_with_wrappers//
// return executor(sql, params, many, context)//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/backends/utils.py",
line 84, in _execute//
// return self.cursor.execute(sql, params)//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/utils.py",
line 90, in __exit__//
// raise dj_exc_value.with_traceback(traceback) from exc_value//
// File
"/home/damiano/.virtualenvs/myproj/lib/python3.8/site-packages/django/db/backends/utils.py",
line 84, in _execute//
// return self.cursor.execute(sql, params)//
//django.db.utils.ProgrammingError: ERRORE: elemento FROM per la
tabella "t4" mancante//
//LINE 1: ... "base_c" bla ON ("base_a"."id" = bla."a_id" AND
(T4."value".../
^
there is no T4 on the previous qs.query, but i try again and the sql
output is magically *_changed_*. (why?)
/>>> str(qs.query)//
//'SELECT "base_a"."id", "base_a"."foo", bla."id", bla."a_id",
bla."b_id" FROM "base_a" LEFT OUTER JOIN "base_c" bla ON ("base_a"."id"
= bla."a_id" AND (T4."value" = 1))'/
_*NOTE:*_
I also tested the code changing:
//.annotate(bla=FilteredRelation('c', condition=Q(c__b__value=1)))/
/
//with
/.annotate(bla=FilteredRelation('c__b', condition=Q(c__b__value=1)))/
In this case it works but it adds the B fields on the SELECT... i do not
need them i just need to add that model on the condition without having
its fields, _I just need fields of A and fields of __/C/_/
/
are they bugs?
D.
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