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Django ORM using external database to unmanaged model in view says relation does not exist

I have two Postgres database connections and when using another than default ORM calls fail on views, but not raw. I am using docker and containers are connected and using Django's own runserver command. Using ORM in django command or django shell works fine, but not in a view.
As a side note, both databases are actually Django-projects, but main project is reading some data directly from another project's database using own unmanaged model.
Python: 3.9.7
Django: 3.2.10
Postgres: 13.3 (main project), 12.2 (side project)
# settings
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql',
'USER': 'pguser',
'PASSWORD': 'pguser',
'NAME': 'mainproject',
'HOST': 'project-db', # docker container
'PORT': '5432',
},
'external': {
'ENGINE': 'django.db.backends.postgresql',
'USER': 'pguser',
'PASSWORD': 'pguser',
'NAME': 'sideproject',
'HOST': 'side-db', # docker container, attached to same network
'PORT': '5432',
},
}
# My unmanaged model
class MyTestModel(models.Model):
​
class Meta:
# table does not exist in 'default', but it does exist in 'external'
db_table = 'my_data_table'
managed = False
# my_data_table is very simple it has id field as integer
# and primary key (works out of the box with django)
# it has normal fields only like IntegerField or CharField
# But even if this model is empty then it returns normally the PK field
# My custom command in Main project
# python manage.py mycommand
# ...
def handle(self, *args, **options):
# This works fine and data from external is populated in MyTestModel
data = MyTestModel.objects.using('external').all()
for x in data:
print(x, vars(x))
# My simple view in Main project
class MyView(TemplateView):
# But using example in views.py, random view class:
def get(self, request, *args, **kwargs):
# with raw works
data = MyTestModel.objects.using('external').raw('select * from my_data_table')
for x in data:
print(x, vars(x))
# This does not work
# throws ProgrammingError: relation "my_data_table" does not exist
data = MyTestModel.objects.using('external').all()
for x in data:
print(x, vars(x))
return super().get(request, *args, **kwargs)
So somehow runserver and views does not generate query correctly when using ORM. It cannot be a connection error, because when running command or view with ".raw()" works.
Now the funny thing is that if I change "db_table" to something what is common in both database lets say "django_content_type" ORM "filter()" and "all()" works in view too. And yes then it actually returns data from correct database. So if main project has 50 content types and side project (external) has 100 content types it actually returns those 100 content types from external.
I have tried everything, rebuilding docker, creating new tables to database directly, force reload postgres user and made sure all is owner permissions and all permissions (should be ok anyway because command side works). I even tried to use another database.

I know I didn't post the full settings and my local settings which could have helped more to solve this case.
But I noticed that I had installed locally Django Silk, which captures the request and tries to analyze called database queries. Looks like it may have been loaded too early or it doesn't like external databases. But disabling Django silk from installed apps and removing it's middleware removed the problem.

Django database tables being created under incorrect schema

I created a Django application and connected it to SQL Server with a trusted connection. When I migrate, Django is creating a new schema name (trusted connection username) in the database and adding this on all tables as prefix. By my IT department convention, all tables should be created with the 'dbo' prefix.
The most interesting part is: When I access the database from SSMS (also with trusted connection), and create a new database, I do not have this issue, it creates as 'dbo.table_name'.
Does anybody knows how can I fix it? See below better example and some code.
Summary:
Django creating: 'my_username.table_name'
I need: 'dbo.table_name'
My django settings.py
DATABASES = {
'default': {
'ENGINE': 'sql_server.pyodbc',
'NAME': 'dabase_name',
'HOST': 'database_host',
'USER': '',
'OPTIONS': {
'driver': "ODBC Driver 17 for SQL Server",
'Trusted_Connection' : 'Yes',
}
}
}
One of my models (table) as example:
class Sap_module(models.Model):
sap_module = models.CharField(max_length=2, unique=True)
available = models.BooleanField(default=True)
def __str__(self):
return self.sap_module

Is there any method in django to use database without creating models.py file?

I am having a database with some data filled in it and i want to use it in my new django app. So is their any way to use data of database in my django app.Actually i don't want to make any changes in my old database and only want to use its data. Anybody please suggest me what will be the better approach to do this.
While serching i also found a command-inspectdb
which can generate model.py file from database, but their are some issues with it that it does'nt map the foreign key in model.py, we need to rearrange our classes in model.py file and some more. So i am searching for some other alternative.

You could access data from legacy database using connection.cursor() from django.db module.
If you have two dabases
DATABASES = {
'default': {
'NAME': 'new_database',
'ENGINE': 'django.db.backends.postgresql_psycopg2',
'USER': '',
'PASSWORD': ''
},
'old': {
'NAME': 'old_database',
'ENGINE': 'django.db.backends.mysql',
'USER': '',
'PASSWORD': ''
}
}
...
from django.db import connections
cursor = connections['old'].cursor()
cursor.execute("SELECT...")
cursor.fetchall()
refer to docs:
Executing custom SQL directly
Multiple databases
But if you want to modify data in your old database it is better idea to create models.py file and use it as always. Using inspectdb or not is up to you. For example you cold generate model using inpsectdb in separate temporary project, make dumpdata to create json files and upload data to your active project somehow.

How to get the database where a model instance was saved to in Django?

I have a django application using multiple databases. Given an instance of a model, how can I obtain the database where it is stored (if any)? I need this to save another object to the same database as the first.
def add_ducks_to_hunt(hunter):
db = # the hunter's db
duck = Duck()
duck.save(using=db)

Use _state.db, as in:
my_obj = MyModel.objects.get(pk=1)
my_obj._state.db
This is shown in the routing example.

I believe you are looking for settings.py in the project (top level) Django directory. If not, would you post more information?
Here is a bit of my settings.py file in the Django project directory /home/amr/django/amr.
import os
DEBUG = True
TEMPLATE_DEBUG = DEBUG
ADMINS = (
# ('Somone R. Somebody'so-forath-and-so-and-so#somewhere.com'),
)
MANAGERS = ADMINS
DATABASES = {
'default': {
#'ENGINE': 'django.db.backends.', # Add 'postgresql_psycopg2', 'postgresql', 'mysql', 'sqlite3' or 'oracle'.
'ENGINE': 'mysql',
'NAME': 'some-server-name', # Or path to database file if using sqlite3.
'USER': '<user>', # Not used with sqlite3.
'PASSWORD': 'xxxxxxxx', # Not used with sqlite3.
'HOST': '', # Set to empty string for localhost. Not used with sqlite3.
'PORT': '', # Set to empty string for default. Not used with sqlite3.
}
}
SESSION_COOKIE_AGE = 15 * 60 * 60 # Age of cookie, in seconds

If you always save a model in the same db, you could store that info in model class and then use it when needed. Probably not very pythonic, but it may do the trick.
Class Hunter(models.Model):
# ... other stuff
db = 'hunter_db'
Access it then with __class__:
def add_ducks_to_hunt(hunter):
db = hunter.__class__.db
duck = Duck()
duck.save(using=db)
On the other hand, if you save objects of one class in different databases, than I see no other way than to write each object's id and db name at object's save() to a table somewhere you can always access it and use that info to load the object.

There is no way to directly get the info from a model instance itself. Ah, _state, yes. its You should explicitly pass in 'using' parameter, just like those built-in methods. Or design router which could deduce the DB to use by check some facts of the model instance, here the hunter.

Assuming you have multiple databases, and you've defined a router, then you can just query your router like:
from myrouters import MyRouter
from myapp.models import Duck
using = MyRouter().db_for_write(Duck)
duck = Duck()
duck.save(using=using)
That said, I'm not sure why you'd need to do this. If the model exists on one database, and you've properly defined a router, then this should be unnecessary. Django will automatically lookup the correct default value for using. If the model exists on multiple databases simultaneously and want to control the specific database where it's written to, then you should already know which database you want to use and shouldn't need to query it.

How to use schemas in Django?

I whould like to use postgreSQL schemas with django, how can I do this?

Maybe this will help.
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql_psycopg2',
'OPTIONS': {
'options': '-c search_path=your_schema'
},
'NAME': 'your_name',
'USER': 'your_user',
'PASSWORD': 'your_password',
'HOST': '127.0.0.1',
'PORT': '5432',
}
}
I get the answer from the following link:
http://blog.amvtek.com/posts/2014/Jun/13/accessing-multiple-postgres-schemas-from-django/

I've been using:
db_table = '"schema"."tablename"'
in the past without realising that only work for read-only operation. When you try to add new record it would fail because the sequence would be something like "schema.tablename"_column_id_seq.
db_table = 'schema\".\"tablename'
does work so far. Thanks.

As mentioned in the following ticket:
https://code.djangoproject.com/ticket/6148, we could set search_path for the django user.
One way to achieve this is to set search_path via psql client, like
ALTER USER my_user SET SEARCH_PATH TO path;
The other way is to modify the django app, so that if we rebuild the database, django won't spit all the tables in public schema.
To achieve this, you could override the DatabaseWrapper defined in django.db.backends.postgresql_psycopg2.base
Create the following directory:
app/pg/
├── __init__.py
└── base.py
Here's the content of base.py
from django.db.backends.postgresql_psycopg2.base import DatabaseWrapper
class DatabaseWrapper(DatabaseWrapper):
def __init__(self, *args, **kwargs):
super(DatabaseWrapper, self).__init__(*args, **kwargs)
def _cursor(self):
cursor = super(DatabaseWrapper, self)._cursor()
cursor.execute('SET search_path = path')
return cursor
In settings.py, add the following database configuration:
DATABASES = {
'default': {
'ENGINE': 'app.pg',
'NAME': 'db',
'USER': 'user',
'PASSWORD': '',
'HOST': '',
'PORT': '',
}
}

It's a bit more complicated than tricky escaping. Have a look at Ticket #6148 in Django for perhaps a solution or at least a patch. It makes some minor changes deep in the django.db core but it will hopefully be officially included in django.
After that it's just a matter of saying
db_schema = 'whatever_schema'
in the Meta class or for a global change set
DATABASE_SCHEMA = 'default_schema_name'
in settings.py
UPDATE: 2015-01-08
The corresponding issue in django has been open for 7 years and the patch there will not work any more.
The correct answer to this should be...
At the moment you can't use postgreSQL schemas in django out of the box.

I just developed a package for this problem: https://github.com/ryannjohnson/django-schemas.
After some configuration, you can simply call set_db() on your models:
model_cls = UserModel.set_db(db='db_alias', schema='schema_name')
user_on_schema = model_cls.objects.get(pk=1)
The package uses techniques described in https://stackoverflow.com/a/1628855/5307109 and https://stackoverflow.com/a/18391525/5307109, then wraps them for use with Django models.

I've had some success just saying
db_table = 'schema\".\"tablename'
in the Meta class, but that's really ugly. And I've only used it in limited scenarios - it may well break if you try something complicated. And as said earlier, it's not really supported...

There is no explicit Django support for postgreSQL schemas.
When using Django (0.95), we had to add a search_path to the Django database connector for PostgreSQL, because Django didn't support specifying the schema that the tables managed by the ORM used.
Taken from:
http://nxsy.org/using-postgresql-schemas-with-sqlalchemy-and-elixir
The general response is to use SQLAlchemy to construct the SQL properly.
Oh, and here's another link with some suggestions about what you can do with the Django base, extending it to try to support your scheme:
http://news.ycombinator.com/item?id=662901

I know that this is a rather old question, but a different solution is to alter the SEARCH_PATH.
Example
Lets say you have three tables.
schema1.table_name_a
schema2.table_name_b
table_name_c
You could run the command:
SET SEARCH_PATH to public,schema1,schema2;
And refer to the tables by their table names only in django.
See 5.7.3. The Schema Search Path

For SQL server database:
db_table = "[your_schema].[your_table]"

https://docs.djangoproject.com/en/dev/topics/db/multi-db/#using-routers
urls.py
from django.urls import path, include
from rest_framework.routers import DefaultRouter
from my_app.my_views import ClientViewSet
router = DefaultRouter(trailing_slash=False)
router.register(r'', ClientViewSet, base_name='clients')
urlpatterns = [
path('', include(router.urls)),
]