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Switch to another database in Django

I have a django project that was created on an Oracle database and I want to switch to ANOTHER Oracle database. I have followed this tutorial https://pythonfusion.com/switch-database-django/, but there is a problem that not all models are created initially in Django, some are created using inspectdb on existing tables in other databases . Therefore, when using the migrate --database=new command, I get errors about those tables that already existed before Django was created. Is there a way to migrate only the models and tables necessary for Django to work? (users, auth...)

I think you have to take a look at the managed attribute of each model meta class.
If managed is true then django will change the model in the database.
Unmanaged model :
class MyModel(models.Model):
...
class Meta:
managed = False # This means django will ignore MyModel when migrating
Managed model :
class MyManagedModel(models.Model):
...
class Meta:
managed = True # This means django will migrate MyManagedModel
More documentation here : https://docs.djangoproject.com/en/4.1/ref/models/options/

Yes you can definitely customize your migration behavior, the command python manage.py makemigrations creates a couple of files that are used to migrate your models into your DB, any who you can still access these files and choose exactly what to include, exclude and even edit them.
Check the following link:
https://dev.to/koladev/writing-custom-migrations-in-django-3eli

If I've understood your question correctly, then you're looking to use Django's built-in migrations. To find out which migrations have been run against your new database, run the command manage.py showmigrations --database=new which will show you a list of all migrations that exist within the context of your application.
Once that is done, you can manually run the desired migrations (e.g. auth and contenttypes) by running the command manage.py migrate --database=new app_label migration_name.
showmigrations command: https://docs.djangoproject.com/en/4.1/ref/django-admin/#django-admin-showmigrations
migrate command: https://docs.djangoproject.com/en/4.1/ref/django-admin/#django-admin-migrate

Django Models UnManaged to Managed

Does changing Django Model from managed=False to managed=True affect the data ?
I have a large table of a Model that has managed=False and want to add a new field to it. adding a field using migration can't be done without changing the model to managed=True
Is it safe to just change it to managed=True , migrate the change, then update fields ?

Yes. It is safe and required. I have read django documentation about your problem. That says that:
Managed option defaults to True, meaning Django will create the
appropriate database tables in migrate or as part of migrations and
remove them as part of a flush management command. That is, Django
manages the database tables’ lifecycles.
If False, no database table creation, modification, or deletion
operations will be performed for this model.
If your django model option managed=False then make it managed=True, otherwise your migration of models won't work. For more info read django documentation.

Django - delete M2M field but keep join table

is it possible to remove an M2M field from a model and keep the joining table?
context:
I am trying to add through model to existing M2M field like described in this post
But doing it simply like this will result in a production app crash when accessing the old table during deployment - short window between migration and code update, when old code will try to access a new database for a few moments - without the old table in it.

You can use --fake flag when running manage.py migrate. That will make a migration file that says the model field has been removed and mark it as applied in the database migration table, but not actually execute the SQL to remove the corresponding tables etc. Read more here

How to use Django with an existing database in MySQL?

I have an application in Django 2.0 and as a database engine I use MySQL. I have a problem because the database was previously created and already has records, my idea is to use this same database for the application I am creating.
Use the command
python manage.py inspectdb > models.py
To create the models.py file which will be cleaned as indicated by the models.py file that was generated.
#This is an auto-generated Django model module.
# You'll have to do the following manually to clean this up:
# * Rearrange models' order
# * Make sure each model has one field with primary_key=True
# * Make sure each ForeignKey has `on_delete` set to the desired behavior.
# * Remove `managed = False` lines if you wish to allow Django to create, modify, and delete the table
# Feel free to rename the models, but don't rename db_table values or field names.
After this I proceed to execute:
python manage.py migrate
python manage.py makemigrations
python manage.py migrate
But it generates the following error:
(1050, "Table 'XXXXXXX' already exists")
Obviously it tells me that the table already exists, but how do I not generate this error and continue administering the tables from Django.

You need to run --fake-initial or --fake. See more at Django migrations. Be careful because running inspectdb doesn't solve all your problems. You need to fix the things inside models.py manually and migrate again.

One of the things (and the main reason I do not use Django) is it likes to take control of everything. The fact that it controls the database means that if you don't start strictly in Django, you are doing it wrong.
However there is a work around:
https://docs.djangoproject.com/en/2.0/howto/legacy-databases/

django: exclude models from migrations

In my django application (django 1.8) I'm using two databases, one 'default' which is MySQL, and another one which is a schemaless, read-only database.
I've two models which are accessing this database, and I'd like to exclude these two models permanently from data and schema migrations:
makemigrations should never detect any changes, and create migrations for them
migrate should never complain about missing migrations for that app
So far, I've tried different things, all without any success:
used the managed=False Meta option on both Models
added a allow_migrate method to my router which returns False for both models
Does anyone have an example of how this scenario can be achieved?
Thanks for your help!

So far, I've tried different things, all without any success:
used the managed=False Meta option on both Models
That option (the managed = False attribute on the model's meta options) seems to meet the requirements.
If not, you'll need to expand the question to say exactly what is special about your model that managed = False doesn't do the job.

I thought, I have a problem with makemigrations. It pretends to make migration on managed = False model, but no SQL code generated for this model
Here is my example, model Smdocumets unmanaged, and no SQL code was generated.
python manage.py makemigrations
Migrations for 'monitor':
monitor\migrations\0005_auto_20171102_1125.py
- Create model Smdocuments
- Add field sid to db
- Alter field name on db
python manage.py sqlmigrate monitor 0005
BEGIN;
--
-- Create model Smdocuments
--
--
-- Add field sid to db
--
ALTER TABLE "monitor_db" RENAME TO "monitor_db__old";
...

You have the correct solution:
used the managed=False Meta option on both Models
It may appear that it is not working but it is likely that you are incorrectly preempting the final result when you see - Create model xxx for models with managed = False when running makemigrations.
How have you been checking/confirming that migrations are being made?
makemigrations will still print to terminal - Create model xxx and create code in the migration file but those migrations will not actually result in any SQL code or appear in Running migrations: when you run migrate.