unresolved attribute "Column" in class "SQLAlchemy"

Question

i use pycharm 5.0 and python3.5.And i download all the liarbry by the build-in function of pycharm(setting-project-project interpreter-"+").other libraries appear well,but some problems happens to flask-SQLAlchemy.

i import flask-SQLAlchemy successfully.however,pycharm remind me that "unresolved attribute reference 'Column' in class'SQLAlchemy'"."unresolved attribute reference 'relationship' in class 'SQLAlchemy'" and so on.

I have try some ways ,but they didn't work.for example:1.restart 2.remove and redownload 3.refresh the cache.which mention in PyCharm shows unresolved references error for valid code

code:

from flask import Flask, redirect, render_template, session, url_for, flash
from flask_sqlalchemy import SQLAlchemy
from flask_bootstrap import Bootstrap
from flask_wtf import Form
from wtforms import StringField, SubmitField
import os
from wtforms.validators import data_required


basedir = os.path.abspath(os.path.dirname(__file__))


app = Flask(__name__)
app.config['SECRET_KEY'] = 'hard to guess string'
app.config['SQLALCHEMY_DATABASE_URI'] =\
    'sqlite:///' + os.path.join(basedir, 'data.sqlite')
app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True


bootstrap = Bootstrap(app)

db = SQLAlchemy(app)


class Role(db.Model):
    __tablename__ = 'roles'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64), unique=True)
    users = db.relationship('User', backref='role', lazy='dynamic')

    def __repr__(self):
        return '<Role %r>' % self.name


class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), unique=True, index=True)
    role_id = db.Column(db.Integer, db.ForeignKey('roles.id'))

    def __repr__(self):
        return '<User %r>' % self.username

how can i solve this problem?

Answer 1

The constructor of the flask_sqlalchemy.SQLAlchemy class calls _include_sqlalchemy, which attaches all attributes from sqlalchemy and sqlalchemy.orm to its instances.

This is only done at runtime and not detected by PyCharm's code inspection.

It would require flask_sqlalchemy to use a more standard way of importing those attributes, like from sqlalchemy import *. But this would import the attributes into the flask_sqlalchemy module instead of each instance of SQLAlchemy and thus change the way they're accessed.

I'm not a Python or SQLAlchemy expert and won't judge whether this is good design or not but you could open an issue on https://github.com/pallets/flask-sqlalchemy and discuss it there.

Answer 2

here is what I do.

from flask_sqlalchemy import SQLAlchemy
from typing import Callable


class MySQLAlchemy(SQLAlchemy):  # Or you can add the below code on the SQLAlchemy directly if you think to modify the package code is acceptable.
    Column: Callable  # Use the typing to tell the IDE what the type is.
    String: Callable
    Integer: Callable


db = MySQLAlchemy(app)


class User(db.Model, UserMixin):
    __tablename__ = "users"
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(20))  # The message will not show: Unresolved attribute reference 'Column' for class 'SQLAlchemy' 

    def __init__(self, *args, **kwargs): 
        super().__init__(*args, **kwargs)


def create_test_data():
    db.create_all()
    test_user = User(name='Frank')  # I add __init__, so it will not show you ``Unexpected argument``
    db.session.add(test_user)
    db.session.commit()