I need help with shared models

[XCanG]

I have a project with FastAPI backend and integration bots, they all share the same model files from a root project, however when I tried to add Piccolo integration I immediately stumbled upon those Apps and that those apps has to be unique. If I use one name for them then I get error like ValueError: There are 2 apps with the name app. This can cause unexpected behavior. Make sure each app has a unique name, and you haven't registered the same app multiple times.

But if I use different name then I get duplicate migrations, e.g. I make a migration with: piccolo migrations new app --auto I get one file with all tables, then when I do check it shows me multiple entries for the same migration.
My project structure is like that:

db/
  |+migrations/
  |  |+__init__.py (migrations created there)
  |+models.py (shared models here)
integration1/
  |+piccolo_app.py
backend/
  |+piccolo_app.py
|-piccolo_conf.py

My piccolo_app.py have this app config:

APP_CONFIG = AppConfig(
    app_name="app",
    migrations_folder_path=Path("db") / "migrations",
    table_classes=table_finder(
        modules=["db.models"],
        # package=get_package(__name__),
        exclude_imported=True,
    ),
    migration_dependencies=[],
    commands=[],
)

Root folder db have models file with shared models, the same config duplicated in other integrations with exception of app_name.

I need a way to import Piccolo everywhere, but I don't need separate migrations and duplicates.

[sinisaos]

@XCanG Piccolo has the concept of an apps to separate code into separate logical units. In your case (if I understand correctly) you need one central application (called a db with migrations and tables) that shares tables with other applications.
I think you should do something like this. This is the project tree

tree
.
├── backend
│   ├── __init__.py
│   ├── main.py
│   └── piccolo_app.py
├── db
│   ├── __init__.py
│   ├── piccolo_app.py
│   ├── piccolo_migrations
│   │   ├── db_2025_08_11t07_30_57_292674.py
│   │   └── __init__.py
│   └── tables.py
├── integration1
│   ├── __init__.py
│   ├── main.py
│   └── piccolo_app.py
├── main.py
└── piccolo_conf.py

As you can see, only the db application has a tables.py and a migrations folder. In your db.tables, put your tables (in this example I'm using a simple Task table) and make the migrations (piccolo migrations new db --auto and piccolo migrations forwards db)
To share tables from db/tables.py you need to do something like this. In backend/piccolo_app.py and integration1/piccolo_app you just need to set the positional arguments app_name and migrations_folder_path to an empty string (because we don't have migrations in that apps)

from piccolo.conf.apps import AppConfig

APP_CONFIG = AppConfig(
    app_name="backend", # or app_name="integration1"
    migrations_folder_path="",
)

Now you can import APP_CONFIG or db.tables into backend/main.py

from db.piccolo_app import APP_CONFIG
from db.tables import Task

task_tables = APP_CONFIG.table_classes
tasks = Task.select().run_sync()

Then put the main input file main.py in the root and you will be able to print variables from backend/main.py (or integration1/main.py).

from backend.main import task_tables, tasks
from integration1.main import tables_columns

print(tasks)
print(task_tables)
print(tables_columns)

I hope this helps and I apologize if I didn't get your point.

[XCanG]

I did try your solution with "" as path, but I get error FileNotFoundError: [WinError 3] System cannot find specified path: "" when I tried to run piccolo commands

[XCanG]

Theoretically this would be what I need, but as expected it didn't work. If there were type hint with None I would expect that there would be such a case.

[sinisaos]

Sorry, but I don't use Windows. On Linux, in my case everything works. In fact, even if I use None and set migrations_folder_path=None, everything works too. That's a bit strange because migrations_folder_path is union of str and Path

piccolo/piccolo/conf/apps.py

Line 185 in 5139ec0

migrations_folder_path: Union[str, pathlib.Path]

Can you try that? If it doesn't work, can you try updating your local Piccolo installation with migrations_folder_path: Union[str, pathlib.Path, None] and see if it works? That will be useful (you can try on Windows, I can't) because there was a issue for disabling migrations. Thanks in advance.

[XCanG]

Hm, None case looks like working, at least don't throw exceptions right away, but type checker will show error there.

Regarding OS: I develop on Windows first, but then I deploy in Docker, so editing a lib locally isn't an option. If it can be pushed directly to the lib then that would be great.

[sinisaos]

I see no reason why you shouldn't make a PR with that change and let Piccolo author look at that.