There is no data in the database created by flask_sqlalchemy?

I encountered a problem when I used flask_sqlalchemy for the first time, as follows

uses python version 3.6 , uses conda as the package manager, and has successfully installed flask_sqlalchemy and other related dependent packages.

the simple directory of the project is as follows: 

app.py
db/
models/
    __init__.py
    todo.py
routes/
    __init__.py
    todo.py
static/
templates/

app.py the contents of the file are as follows: 

>>> from app import db
>>> db.create_all()

problems are as follows:
check the file directory at this time and find that there is a data.sqlite file under models/ , but there is no content in the file, the display size is 0 byte , and I use database management software to check and find that there is no data in any table. At the same time, if I continue to execute db.drop_all , I cannot delete the database file.

I would like to ask how to solve this situation. I Googled it and couldn"t find the answer. I hope I can get some advice from my predecessors. I would appreciate it.

Python python3.x flask sqlalchemy sqlite3
Jun.25,2022

you have to declare the model structure before calling db.create_all () .

like this 

from app import db
from models import todo
db.create_all()
One of the seniors at the bottom of

has answered quite well, and I have also found some related articles in stackoverflow . At the same time, there is another mistake in my own code. Let me sum it up:

if I quote db in app.py in models/todo.py and the module in models in app.py , resulting in circular references reporting errors, I think it's better to do this:

.
  • initialize db in models , where db can be initialized without app , as follows 
   create_all ()  Import the data file before

Previous: The Typescript `type "String" cannot be used as an index type. `

Next: How to shut down gunicorn safely and gracefully

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e8a4af-5bde1.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e8a4af-5bde1.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?