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How to get table alias for inner join in django

I'm using django 2.1, python 3.6 and SQL Server 2012 as backend. I have following models:
class ModelA(models.Model):
name = models.CharField(...)
value = models.PositiveIntegerField(...)
class ModelB(models.Model):
name = models.CharField(...)
values = models.ManyToManyField(ModelA, through='ModelC')
class ModelC(models.Model):
model_a = models.ForeignKey(ModelA, ...)
model_b = models.ForeignKey(ModelB, ...)
info_a = models.CharField(...)
info_b = models.CharField(...)
How can I achieve following SQL query:
SELECT t1.model_a_id AS a_id, t3.value AS a_value
FROM ModelB AS t0
INNER JOIN ModelC t1 ON t1.model_b_id = t0.id
INNER JOIN ModelC t2 ON t2.model_b_id = t0.id
INNER JOIN ModelA t3 ON t3.id = t2.model_a_id
INNER JOIN ModelC t4 ON t4.model_b_id = t0.id
WHERE t1.model_a_id in (1,2) AND t2.model_a_id in (8,9,10,11) AND t4.model_a_id in (21,22)
What I have so far:
ModelB.objects.filter(values__in=[1,2]).filter(values__in=[8,9,10,11]).filter(values__in=[21,22])
Which produces the correct filtered QuerySet. But how can I get the correct fields?
I tried to use annotate function but I failed. Using django's Subquery as described in the docs generates database error, because SQL Server does not support subqueries in the SELECT part.
Any recommendations? Thanks!

I solved it without falling back to raw sql. I used django's FilteredRealtion objects in combination of additional annotate like this:
from django.db.models import Q, F, FilteredRelation
qs = ModelB.objects.filter(values__in=[21,22])
qs = qs.filter(values__in=[1,2])
qs = qs.filter(values__in=[8,9,10,11])
qs = qs.annotate(_a_id=FilteredRelation('modelc', condition=Q(values__in=[8,9,10,11])),
_a_value=FilteredRelation('modelc', condition=Q(values__in=[1,2])))
qs = qs.annotate(a_id=F('_a_id__model_a'), a_value=F('_a_value__model_a__value'))
qs = qs.values('a_id', 'a_value')

Your query is not optimal, but that's a different issue.
You can try raw query
So you can run:
query = """
SELECT t1.model_a_id AS a_id, t3.value AS a_value
FROM ModelB AS t0
INNER JOIN ModelC t1 ON t1.model_b_id = t0.id
INNER JOIN ModelC t2 ON t2.model_b_id = t0.id
INNER JOIN ModelA t3 ON t3.id = t2.model_a_id
INNER JOIN ModelC t4 ON t4.model_b_id = t0.id
WHERE t1.model_a_id in ({0}) AND t2.model_a_id in ({1}) AND t4.model_a_id in
({2})"""
t1_filters = ','.join(['1','2'])
t2_filters = ','.join(['8', '9', '10', '11'])
t4_filters = ','.join(['21', '22'])
results = ModelA.objects.raw(query.format(t1_filters, t2_filters, t4_filters))
for instance in results.all():
print(instance)

Django 1.11.4 Postgresql SELECT ARRAY to django orm

I am trying to build a complex(for me) query for one of my projects. Django version is 1.11.4 and PostgreSQL version is 9.6.
Here are the models.
class Event(models.Model):
...
name = models.CharField(max_length=256)
classification = models.ForeignKey("events.Classification", related_name="events", null=True, blank=True)
...
class Classification(models.Model):
...
segment = models.ForeignKey("events.ClassificationSegment", related_name="classifications", blank=True, null=True)
...
class ClassificationSegment(models.Model):
...
name = models.CharField(max_length=256)
...
I blocked somewhere here and can't go ahead.
from django.db.models import CharField, Value as V
from django.db.models.functions import Concat
from django.contrib.postgres.aggregates import ArrayAgg
from django.db.models import OuterRef, Subquery
import events.models
event_subquery = events.models.Event.objects.filter(classification__segment=OuterRef('pk')) \
.annotate(event=Concat(V('{id:'), 'id', V(', name:"'), 'name', V('"}'), output_field=CharField()))
final_list = events.models.ClassificationSegment.objects.annotate(
event_list=ArrayAgg(Subquery(event_subquery.values('event')[:6])))
I have a raw query. Here it is.
final_events = events.models.ClassificationSegment.objects.raw('SELECT "events_classificationsegment"."id", "events_classificationsegment"."name", (SELECT ARRAY(SELECT CONCAT(\'{id:\', CONCAT(U0."id", CONCAT(\',\', \'name:"\', U0."name", \'"}\'))) AS "event" FROM "events_event" U0 INNER JOIN "events_classification" U1 ON (U0."classification_id" = U1."id") WHERE U1."segment_id" = ("events_classificationsegment"."id") LIMIT 6)) AS "event_list" FROM "events_classificationsegment"')
You can see the result in the screenshot. I guess I am on the right way. Can anyone help me?
Thanks.

Postgres has a really nice way of making an array from a subquery:
SELECT foo.id, ARRAY(SELECT bar FROM baz WHERE foo_id = foo.id) AS bars
FROM foo
To do this within the ORM, you can define a subclass of Subquery:
class Array(Subquery):
template = 'ARRAY(%(subquery)s)'
and use this in your queryset:
queryset = ClassificationSegment.objects.annotate(
event_list=Array(event_subquery.values('event')[:6])
)

how to make left join in django?

this is my first model
class DipPegawai(models.Model):
PegID = models.AutoField(primary_key=True)
PegNamaLengkap = models.CharField(max_length=100, blank=True, null=True)
PegUnitKerja = models.IntegerField(null=True,blank=True)
and this is my second model
class DipHonorKegiatanPeg(models.Model):
KegID = models.AutoField(primary_key=True)
PegID = models.ForeignKey(DipPegawai, blank=True,null=True)
KegNama = models.Charfield(max_length=100,null=True,blank=True)
i want to make left join with this model, something like this in mysql query
SELECT PegNamaLengkap, KegNama_id
FROM karyawan_dippegawai AS k LEFT JOIN honorkegiatanpeg_diphonorkegiatanpeg AS h ON k.PegID = h.PegID_id
WHERE PegUnitKerja = 3
GROUP BY k.PegID
how to make left join with django orm same like mysql query above?

Should be something like:
DipPegawai.objects.filter(PegUnitKerja=3).values_list.('pegnamalengkap', 'diphonorkegiatanpeg_kegnama')
Tell me if that worked for you.
You can print your raw query using print(your_var_here.query). Remember put your query into a var

DipHonorKegiatanPeg.objects.filter(PegID__PegUnitKerja=3).values('PegID__PegNamaLengkap', 'KegNama_id')

LEFT JOIN with OR condition in python django

All I want is to write the following SQL query in Python Django syntax. I researched a lot but could not get the result I want. Could you please help me.
SELECT * FROM thread
LEFT JOIN user
ON (thread.user1_id = user.id OR thread.user2_id = user.id)
WHERE user.id = 9
My model:
class Thread(models.Model):
last_message = models.TextField(max_length=100)
user1_id = models.IntegerField()
user2_id = models.IntegerField()

The exact query cannot be created using the Django ORM without resorting to some raw SQL. The problem is the OR in the join condition.
But, since your not selecting any rows from the user table, you can create a different query with the same results.
Start by defining your models using ForeignKeys.
from django.db import models
from django.contrib.auth.models import User
class Thread(models.Model):
last_message = models.TextField(max_length=100)
user1 = models.ForeignKey(User)
user2 = models.ForeignKey(User)
class Meta:
db_table = 'thread' # otherwise it will be: appname_thread
Then you can preform the query.
from django.db.models import Q
threads = Thread.objects.filter(Q(user1__id=9) | Q(user2__id=9))
The resulting SQL will be something like this:
SELECT * FROM thread
LEFT JOIN user AS user1
ON (thread.user1_id = user1.id)
LEFT JOIN user AS user2
ON (thread.user2_id = user2.id)
WHERE (user1.id = 9 OR user2.id = 9)
You can improve this by avoiding the join altogether.
# note the single underscore!
threads = Thread.objects.filter(Q(user1_id=9) | Q(user2_id=9))
Generating the following SQL.
SELECT * FROM thread
WHERE (user1_id = 9 OR user2_id = 9)
If you need to also obtain the user instances in the same query, in which case you really need the join, you have two options.
Either use the first query that includes joins and afterwards select the correct user based in the id in Python.
for thread in threads:
if thread.user1.id == 9:
user = thread.user1
else:
user = thread.user2
Or use raw SQL to get the exact query you want. In this case, you can use the models without the ForeignKeys as you defined them.
threads = Thread.objects.raw('''
SELECT *, user.id AS user_id, user.name as user_name FROM thread
LEFT JOIN user
ON (thread.user1_id = user.id OR thread.user2_id = user.id)
WHERE user.id = 9''')
for thread in threads:
# threads use the ORM
thread.id
# user fields are extra attributes
thread.user_id
thread.user_name

Joining Multiple Tables in Django

I have looked through around and there doesn't seem to be anything that has exactly answered what I am looking for, using the following model I want to join all the tables:
class A(models.Model):
name = models.CharField(max_length=60)
class B(models.Model):
a = models.ForeignField(A)
class C(models.Model):
a = models.ForeignField(A)
class D(models.Model):
a = models.ForeignField(A)
This is a very basic sort of structure I have going on, I want to join all the tables based on there foreign key link the A. I have looked at select_related but it seems like that is the reverse direction of what I want to do because it links an object to what it references and I want to join based on what references it.
Basically I want to join the tables like this MySQL query:
SELECT * FROM A, B, C, D WHERE A.id = B.aID AND A.id = C.aID AND A.id = D.aID;

You can use a custom join for your purpose:
# assume our models.py contains the following
class Contact(models.Model):
name = models.CharField(max_length=255)
phones = models.ManyToManyField('Phone')
addresses = models.ManyToManyField('Address')
class Phone(models.Model):
number = models.CharField(max_length=16)
# join as follows
contacts = Contact.objects.extra(
select={'phone': 'crm_phone.number'}
).order_by('name')
# setup intial FROM clause
# OR contacts.query.get_initial_alias()
contacts.query.join((None, 'crm_contact', None, None))
# join to crm_contact_phones
connection = (
'crm_contact',
'crm_contact_phones',
'id',
'contact_id',
)
contacts.query.join(connection, promote=True)
# join to crm_phone
connection = (
'crm_contact_phones',
'crm_phone',
'phone_id',
'id',
)
contacts.query.join(connection, promote=True)
Wash, rinse, repeat for every pair of tables till you're happy. If this is too involved, you can always use custom SQL.