I'm working on a flask application where I'm trying to isolate my unit tests. I'm using flask-sqlalchemy, and I'm trying to use the create_all and drop_all methods to clean my database after running a test.
However, it appears my create_all and drop_all methods do not actually create/drop the tables as the documentation states. I have my models imported in the application before calling create_all, like most other answers say.
This is the error I'm getting with the code below:
psycopg2.ProgrammingError: relation "tasks" does not exist
Here's my relevant code
/app.py
import os
import configparser
from flask import Flask
from src.router import router
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
app = Flask(__name__)
if not os.path.exists(os.path.join(app.root_path, 'config.ini')):
raise Exception(f'config.ini not found in the {app.root_path}')
config = configparser.ConfigParser()
config.read('config.ini')
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = config[os.environ['APP_ENV']]['DATABASE_URI']
app.register_blueprint(router)
db = SQLAlchemy(app)
migrate = Migrate(app, db)
if __name__ == "__main__":
app.run()
/tests/test_router.py
from unittest import TestCase
from flask import Flask
from app import app, db
from src.models import Task
class TestRouter(TestCase):
def setUp(self):
db.create_all()
def tearDown(self):
db.drop_all()
def test_adds_task(self):
task = Task(task_id='task_1', name='my task')
db.session.add(task)
db.session.commit()
I think I was a little quick to post the question, but I hope this might help others come up with other ideas on how to troubleshoot a similar issue.
In my src/models.py file where I keep my models, you must make sure that your models are defined correctly. Since Flask-SQLAlchemy is a wrapper around the SQLAlchemy you must use the data types under the db object.
Essentially, I had my models defined as such:
class Task(db.Model):
__tablename__ = 'tasks'
id = Column(Integer, primary_key=True)
task_id = Column(String)
name = Column(String)
created_at = Column(DateTime, default=datetime.datetime.now)
As you can see, I was inheriting from db.Model instead of the return value of declarative_base(). I also needed to add the db. in front of all the data types, including Column, Integer, String, Float, DateTime, relationship, and ForeignKey.
So, I was able to fix my issue by changing my model to something like:
class Task(db.Model):
__tablename__ = 'tasks'
id = db.Column(db.Integer, primary_key=True)
task_id = db.Column(db.String)
name = db.Column(db.String)
created_at = db.Column(db.DateTime, default=datetime.datetime.now)
See: Documentation on declaring Flask-SQLAlchemy models
I am trying to create an application using SQLAlchemy. It worked fine as long as I only had one file with one Class. Now I want to have multiple classes/tables in different files. I stumbled upon this question, and tried to do it like it was suggested there: I now have three files
base.py
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
blind.py
from sqlalchemy import Column, String
from .base import Base
class Blind(Base):
__tablename__ = 'blinds'
blind = Column(String)
data_processor_uuid = Column(String, primary_key=True)
data_source_uuid = Column(String)
timestamp = Column(String, primary_key=True)
and data.py
from sqlalchemy import Column, Integer, String, Float
from .base import Base
class Datum(Base):
__tablename__ = 'data'
data_source_uuid = Column(Integer, primary_key=True)
sensor_type = Column(String)
timestamp = Column(String, primary_key=True)
value = Column(Float)
I now want to initialize the database in db_setup.py using
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from .base import Base
engine = create_engine('sqlite:///test.db', echo=True)
Base.metadata.bind = engine
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
def get_db_session():
return session
This works, however, it does not create the tables in the database as expected. When I try to insert something into the table, I get an error saying "table does not exist". Can someone tell me what I am doing wrong here?
The problem was that I wasn't importing the class definitions for Blinds and Datum anywhere, so they weren't evaluated! Before I split them up into different files, I had imported them to get to Base. Thanks to #IljaEverilä for this answer!
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?
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.
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()
I've ran into the same problem just now.
In short if I just hit Run the code runs with exit code 0 even is PyCharm shows Unresolved attribute reference
but for anyone who might make the same mistake as I did before simply hitting Run:
This is the code that I was writing and it showed 'Unresolved attribute reference 'Column' for class 'SQLAlchemy'' also for eg. 'Unresolved attribute reference 'Integer' for class 'SQLAlchemy' '.
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///new-books-collection.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] =
False
db = SQLAlchemy(app)
class Books(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(250), unique=True, nullable=False)
author = db.Column(db.String(250), unique=True, nullable=False)
rating = db.Column(db.Float, nullable=False)
db.create_all()
My problem was that I hovered over Column and Integer and clicked Add method Column() to class SQLAlchemy. Also the same with Integer.
From that moment TypeErrors came up for me because it created these empty methods in __init__.py of SQLAlchemy.
To solve this I used pip install flask_sqlalchemy --upgrade and pip install flask_sqlalchemy. And did not Add methods again. It still showed Unresolved attribute reference, but the code ran with exit code 0 and the database was created, with the right data inside.
Hope that helps!
Check the version of flask_sqlalchemy in your pycharm or environment.
i had same problem ,the easiest solution
pip install flask_sqlalchemy --upgrade
100% its gone work.
I have some standard SQLAlchemy models that I reuse across projects. Something like this:
from sqlalchemy import Column, Integer, String, Unicode
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Category(Base):
__tablename__ = 'category'
id = Column(Integer, primary_key=True)
slug = Column(String(250), nullable=False, unique=True)
title = Column(Unicode(250), nullable=False)
def __call__(self):
return self.title
I'd like to put this in a shared library and import it into each new project instead of cutting and pasting it, but I can't, because the declarative_base instance is defined separately in the project. If there's more than one, they won't share sessions. How do I work around this?
Here's another question that suggests using mixin classes. Could that work? Will SQLAlchemy accurately import foreign keys from mixin classes?
When you call
Base = declarative_base()
SA create new metadata for this Base.
To reuse your models you must bind metadata of main models to reusable models, but before any import of your reusable models by:
Base.metadata = my_main_app.db.metadata
MixIn classes useful for repeating column declarations, and extending class methods.
For connecting reusable apps based on MixIns you must define concrete class in code manualy for each model.
Will SQLAlchemy accurately import
foreign keys from mixin classes?
MixIn class with foreign key and constraint
from sqlalchemy.schema import UniqueConstraint
from sqlalchemy.ext.declarative import declared_attr
class MessageMixIn(object):
ttime = Column(DateTime)
#declared_attr
def sometable_id(cls):
return Column(Integer, ForeignKey('sometable.id'))
#declared_attr
def __table_args__(cls):
return (UniqueConstraint('sometable_id', 'ttime'), {})
Simplified, I have the following class structure (in a single file):
Base = declarative_base()
class Item(Base):
__tablename__ = 'item'
id = Column(BigInteger, primary_key=True)
# ... skip other attrs ...
class Auction(Base):
__tablename__ = 'auction'
id = Column(BigInteger, primary_key=True)
# ... skipped ...
item_id = Column('item', BigInteger, ForeignKey('item.id'))
item = relationship('Item', backref='auctions')
I get the following error from this:
sqlalchemy.exc.InvalidRequestError
InvalidRequestError: When initializing mapper Mapper|Auction|auction, expression
'Item' failed to locate a name ("name 'Item' is not defined"). If this is a
class name, consider adding this relationship() to the Auction class after
both dependent classes have been defined.
I'm not sure how Python cannot find the Item class, as even when passing the class, rather than the name as a string, I get the same error. I've been struggling to find examples of how to do simple relationships with SQLAlchemy so if there's something fairly obvious wrong here I apologise.
This all turned out to be because of the way I've set SQLAlchemy up in Pyramid. Essentially you need to follow this section to the letter and make sure you use the same declarative_base instance as the base class for each model.
I was also not binding a database engine to my DBSession which doesn't bother you until you try to access table metadata, which happens when you use relationships.
if it's a subpackage class, add Item and Auction class to __init__.py in the subpackage.
The SQLAlchemy documentation on Importing all SQLAlchemy Models states in part:
However, due to the behavior of SQLAlchemy's "declarative" configuration mode, all modules which hold active SQLAlchemy models need to be imported before those models can successfully be used. So, if you use model classes with a declarative base, you need to figure out a way to get all your model modules imported to be able to use them in your application.
Once I imported all of the models (and relationships), the error about not finding the class name was resolved.
Note: My application does not use Pyramid, but the same principles apply.
Case with me
Two models defined in separate files, one is Parent and the other is Child, related with a Foreign Key. When trying to use Child object in celery, it gave
sqlalchemy.exc.InvalidRequestError: When initializing mapper Mapper|Child|child, expression 'Parent' failed to locate a name ("name 'Parent' is not defined"). If this is a class name, consider adding this relationship() to the <class 'app.models.child'>
parent.py
from app.models import *
class Parent(Base):
__tablename__ = 'parent'
id = Column(BigInteger, primary_key=True, autoincrement=True)
name = Column(String(60), nullable=False, unique=True)
number = Column(String(45), nullable=False)
child.py
from app.models import *
class Child(Base):
__tablename__ = 'child'
id = Column(BigInteger, primary_key=True, autoincrement=True)
parent_id = Column(ForeignKey('parent.id'), nullable=False)
name = Column(String(60), nullable=False)
parent = relationship('Parent')
Solution
Add an import statement for Parent in beginning of child.py
child.py (modified)
from app.models import *
from app.models.parent import Parent # import Parent in child.py 👈👈
class Child(Base):
__tablename__ = 'child'
id = Column(BigInteger, primary_key=True, autoincrement=True)
parent_id = Column(ForeignKey('parent.id'), nullable=False)
name = Column(String(60), nullable=False)
parent = relationship('Parent')
Why this worked
The order in which models get loaded is not fixed in SQLAlchemy.
So, in my case, Child was being loaded before Parent. Hence, SQLAlchemy can't find what is Parent. So, we just imported Parent before Child gets loaded.
Namaste 🙏
I've solved the same error by inheriting a 'db.Model' instead of 'Base'... but I'm doing the flask
Eg:
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class someClass(db.Model):
someRelation = db.relationship("otherClass")
Also, even though this doesn't apply to the OP, for anyone landing here having gotten the same error, check to make sure that none of your table names have dashes in them.
For example, a table named "movie-genres" which is then used as a secondary in a SQLAlchemy relationship will generate the same error "name 'movie' is not defined", because it will only read as far as the dash. Switching to underscores (instead of dashes) solves the problem.
My Solution
One models file, or even further, if you need.
models.py
from sqlalchemy import Boolean, BigInteger, Column, DateTime, Float, ForeignKey, BigInteger, Integer, String
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
from .parent import Parent
from .child import Child
parent.py
from sqlalchemy import Boolean, BigInteger, Column, DateTime, Float, ForeignKey, BigInteger, Integer, String
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
#Base = declarative_base()
class Parent(Base):
__tablename__ = 'parent'
id = Column(BigInteger, primary_key=True, autoincrement=True)
name = Column(String(60), nullable=False, unique=True)
number = Column(String(45), nullable=False)
child.py
from sqlalchemy import Boolean, BigInteger, Column, DateTime, Float, ForeignKey, BigInteger, Integer, String
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Child(Base):
__tablename__ = 'child'
id = Column(BigInteger, primary_key=True, autoincrement=True)
parent_id = Column(ForeignKey('parent.id'), nullable=False)
name = Column(String(60), nullable=False)
parent = relationship('Parent')
Why this worked
Same Deepam answer, but with just one models.py file to import another models
I had a different error, but the answers in here helped me fix it.
The error I received:
sqlalchemy.exc.InvalidRequestError: When initializing mapper mapped class Parent->parents, expression 'Child' failed to locate a name ('Child'). If this is a class name, consider adding this relationship() to the <class 'parent.Parent'> class after both dependent classes have been defined.
My set-up is similar toDeepam's answer.
Briefly what I do different:
I have multiple separate .py files for each db.Model.
I use a construct/fill database .py file that pre-fills db.Model objects in either Multi-threading or single threading way
What caused the error:
Only in multi-threaded set up the error occured
This construct/fill .py script did import Parent, but not Child.
What fixed it:
Adding an import to Child fixed it.
I had yet another solution, but this helped clue me in. I was trying to implement versioning, from https://docs.sqlalchemy.org/en/14/orm/examples.html#versioning-objects using the "history_mapper" class.
I got this same error. All I had to do to fix it was change the order in which my models were imported.
Use back_populates for relationship mapping in both models.
Also keep in mind to import both the models in the models/__init__.py
Base = declarative_base()
class Item(Base):
__tablename__ = 'item'
id = Column(BigInteger, primary_key=True)
# ... skip other attrs ...
auctions = relationship('Auction', back_populates='item')
class Auction(Base):
__tablename__ = 'auction'
id = Column(BigInteger, primary_key=True)
# ... skipped ...
item_id = Column('item', BigInteger, ForeignKey('item.id'))
item = relationship('Item', back_populates='auctions')