Imagine that I have one table in my project with some rows in it.
For example:
# -*- coding: utf-8 -*-
import sqlalchemy as sa
from app import db
class Article(db.Model):
__tablename__ = 'article'
id = sa.Column(sa.Integer, primary_key=True, autoincrement=True)
name = sa.Column(sa.Unicode(255))
content = sa.Column(sa.UnicodeText)
I'm using Flask-SQLAlchemy, so db.session is scoped session object.
I saw in https://github.com/zzzeek/sqlalchemy/blob/master/examples/versioned_history/history_meta.py
but i can't understand how to use it with my existing tables and anymore how to start it. (I get ArgumentError: Session event listen on a scoped_session requires that its creation callable is associated with the Session class. error when I pass db.session in versioned_session func)
From versioning I need the following:
1) query for old versions of object
2) query old versions by date range when they changed
3) revert old state to existing object
4) add additional info to history table when version is creating (for example editor user_id, date_edit, remote_ip)
Please, tell me what are the best practicies for my case and if you can add a little working example for it.
You can work around that error by attaching the event handler to the SignallingSession class[1] instead of the created session object:
from flask.ext.sqlalchemy import SignallingSession
from history_meta import versioned_session, Versioned
# Create your Flask app...
versioned_session(SignallingSession)
db = SQLAlchemy(app)
class Article(Versioned, db.Model):
__tablename__ = 'article'
id = sa.Column(sa.Integer, primary_key=True, autoincrement=True)
name = sa.Column(sa.Unicode(255))
content = sa.Column(sa.UnicodeText)
The sample code creates parallel tables with a _history suffix and an additional changed datetime column. Querying for old versions is just a matter of looking in that table.
For managing the extra fields, I would put them on your main table, and they'll automatically be kept track of in the history table.
[1] Note, if you override SQLAlchemy.create_session() to use a different session class, you should adjust the class you pass to versioned_session.
I think the problem is you're running into this bug: https://github.com/mitsuhiko/flask-sqlalchemy/issues/182
One workaround would be to stop using flask-sqlalchemy and configure sqlalchemy yourself.
Related
I'm developing an API with Flask and I cannot retrieve queries from a MySQL database I've connected with flask-sqlalchemy (not sqlalchemy alone). This is a pre-existing database downloaded from my client's PHPMyAdmin, so I haven't ran db.create_all(): I simply created the connection string in config.py, then instantiated db = SQLAchemy() and initialized it (db.init_app(app)) in my factory function (i'm using the factory pattern together with blueprints).
I've already checked and my computer is running the mysql process, the login credentials provided are correct and the database exists in my computer. I'm using MariaDB because I run Manjaro Linux.
This is the connection string, located in config.py:
SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL') or "mariadb+mariadbconnector://dev:dev#localhost/desayunos56"
This is the relevant model. It was created using flask-sqlacodegen and then modified by me to only use the relevant columns within the table. At models.py:
from flask_sqlalchemy import SQLAlchemy
from app import db
# coding: utf-8
t_aus_postmeta = db.Table(
"""
post_id: Order ID
meta_key: Type of value (client name, billing address)
meta_value: Value of meta_key (Name or address itself)
"""
'aus_postmeta',
#db.Column('meta_id', db.BigInteger, nullable=False),
db.Column('post_id', db.BigInteger, nullable=False, server_default=db.FetchedValue()),
db.Column('meta_key', db.String(255, 'utf8mb4_unicode_ci')),
db.Column('meta_value', db.String(collation='utf8mb4_unicode_ci'))
)
And finally, this is the file with the error, views.py. It's a blueprint already registered to __init__.py. I created it only with the intention of checking if I could run queries, but I don't really intend to render anything from Flask:
from flask import render_template
from . import main
from .. import db
from app.models import t_aus_postmeta
#main.route("/", methods=["GET"])
def index():
result = t_aus_postmeta.query_by(post_id=786).first()
This is the error I get: AttributeError: 'Table' object has no attribute 'query_by'
I think it's noteworthy that, although my linter doesn't complain due to unresolved imports, when I use t_aus_postmeta I don't get any method suggestions.
All the questions I've checked are based on using sqlalchemy instead of flask-sqlalchemy. What could be causing this error? At this point, I'm at a loss.
I don't think that's the right way to create your model. Instead you should create it as a class, which will inherit from db.Model, that contains your query_by method.
models.py
class t_aus_postmeta(db.Model):
"""
post_id: Order ID
meta_key: Type of value (client name, billing address)
meta_value: Value of meta_key (Name or address itself)
"""
__tablename__ = 'aus_postmeta'
post_id = db.Column(db.BigInteger(), nullable=False, server_default=db.FetchedValue())
# rest of your columns...
If you do it this way a valid query would look like this:
t_aus_postmeta.query.filter_by('post_id').first()
Notice that this includes tutiplain's suggestion. I think you got your method name wrong. It's just query followed by a filter_by!
I can't find the API reference for the "query_by" method you are using. It seems there is no such method. Perhaps you meant "filter_by" instead?
I am just trying to get started using sqlalchemy. For whatever reason I can't get anything to work.
I installed sqlalchemy the import alone works. I tried to start following the code on this site:
https://www.pythoncentral.io/introductory-tutorial-python-sqlalchemy/
The code is as follows:
import os
import sys
from sqlalchemy import Column, ForeignKey, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy import create_engine
Base = declarative_base()
class Person(Base):
__tablename__ = 'person'
# Here we define columns for the table person
# Notice that each column is also a normal Python instance attribute.
id = Column(Integer, primary_key=True)
name = Column(String(250), nullable=False)
class Address(Base):
__tablename__ = 'address'
# Here we define columns for the table address.
# Notice that each column is also a normal Python instance attribute.
id = Column(Integer, primary_key=True)
street_name = Column(String(250))
street_number = Column(String(250))
post_code = Column(String(250), nullable=False)
person_id = Column(Integer, ForeignKey('person.id'))
person = relationship(Person)
# Create an engine that stores data in the local directory's
# sqlalchemy_example.db file.
engine = create_engine('sqlite:///sqlalchemy_example.db')
# Create all tables in the engine. This is equivalent to "Create Table"
# statements in raw SQL.
Base.metadata.create_all(engine)
I copied and pasted the code to create a table and I'm getting the following error
sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) unable to
open database file (Background on this error at:
http://sqlalche.me/e/e3q8)
I went to http://sqlalche.me/e/e3q8 and it seems to believe that adding pool_pre_ping=True to the engine would help resolve issue. It mentions a connection issues, but don't really understand how that can be since it's just creating the sqlite database.
I would really appreciate any advice on how I can fix this issue.
Edit: I put the specific code into my question.
Also I tried performing the code in pythonanywhere and it works as expected. Any guidance on what could be wrong with my machine would be appreciated.
So for whatever reason I needed to designate the absolute path of where the database needed to be. I updated my engine to be:
sqlite:///C:\user\file_path\test.db
this allowed it to create the database. However I'd really prefer it just create the database in the current directory. If someone knows what I need to do to get that to work that would be great.
I'm using a flask setup from a while and now trying to install Flask-Blogging module on it. Current modules:
- Flask-sqlalchemy with postgres
- Flask-login
- Flask-Blogging (new)
My application.py looks like this:
from flask import Flask
from flask import session
from flask.ext.blogging import SQLAStorage, BloggingEngine
from flask.ext.login import LoginManager
from flask.ext.sqlalchemy import SQLAlchemy
'''
The main application setup. The order of things is important
in this file.
'''
app = Flask(__name__)
app.config.from_object('config.base')
app.config.from_envvar('APP_CONFIG_FILE')
'''
Initialize database
'''
db = SQLAlchemy(app)
'''
Initialize blogger
'''
storage = SQLAStorage(db=db)
blog_engine = BloggingEngine(app, storage)
the last two lines are the only new things I added (other than the imports). Suddenly now I'm getting error about duplicate table names:
sqlalchemy.exc.InvalidRequestError: Table 'customer' is already defined for this MetaData instance. Specify 'extend_existing=True' to redefine options and columns on an existing Table object.
Any ideas what am I doing wrong? I couldn't find much documentation about Flask-Blogging other than:
http://flask-blogging.readthedocs.org/en/latest/
You get this error because in SQLAStorage.__init__ there is this line:
self._metadata.reflect(bind=self._engine)
This will look at your database and create sqlalchemy table things for all the tables currently in your database.
Thus if your database contains a table called 'customer' the line in your code:
storage = SQLAStorage(db=db)
will automatically model an sqlalchemy table called 'customer' for you.
Now... no doubt you have your own database model definitions somewhere, probably in another python module, something like:
class Customer(db.Model):
id = db.Column(db.Integer, primary_key=True)
...
Since this class definition defines a table called 'customer' and since SQLAStorage has already defined a table called 'customer' you get the exception as soon as your class Customer is imported.
Some ways to work around this problem are:
Import your database definition modules before instantiating SQLAStorage
'''
Initialize database
'''
db = SQLAlchemy(app)
import ankit.db_models # import my db models here so SQLAStorage doesn't do it first
'''
Initialize blogger
'''
storage = SQLAStorage(db=db)
blog_engine = BloggingEngine(app, storage)
or
Tell SQLAStorage to use its own metadata
By passing the db param to SQLAStorage.__init__ you are telling it to use your metadata. You can instead just pass the engine parameter and it will create its own metadata.
storage = SQLAStorage(engine=db.engine)
I tried to create a table in the "app" database, but got this error:
app=# CREATE TABLE users;
ERROR: syntax error at or near ";"
LINE 1: LINE 1: CREATE TABLE users;
^
The columns are defined in models.py which is why I don't create them here.
Do not create the tables in PostgreSQL, SQLAlchemy will create the table (and the columns) for you. All you need to do is create the database, which you have done. To create the tables with Flask-SQLAlchemy:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, nullable=False, unique=True)
with app.app_context():
db.create_all()
To address the error (although as stated above you should not do this), it is because that is not a full CREATE TABLE expression. You need to specify zero or more columns for the table.
CREATE TABLE my_table ();
In my case forgot to import my Model class and code
run without any error:).
If you call create_all() on interactive mode please ensure that you import particular Model class.
Note: Every time you make a change on Model class restart ipython.
I have the following mapping (straight from SA examples):
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
fullname = Column(String)
password = Column(String)
I'm working with a MySql DB and the table has an innoDB engine.
I have a single record in my table:
1|'user1'|'user1 test'|'password'
I've opened a session with the following code:
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.engine import create_engine
from sqlalchemy.orm.scoping import scoped_session
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
db_engine = create_engine('mysql://...#localhost/test_db?charset=utf8',echo=False,pool_recycle=1800)
session_factory = sessionmaker(bind=db_engine,autocommit=False,autoflush=False)
session_maker = scoped_session(session_factory)
session = session_maker()
user_1 = session.query(User).filter(User.id==1).one()
user_1.name # This prints: u'user1'
Now, when I change the record's name in the DB to 'user1_change' and commit it and then refresh the object like this:
session.refresh(user_1)
user_1.name # This still prints: u'user1' and not u'user1_change'
It still prints: u'user1' and not u'user1_change'.
What am I missing (or setting up wrong) here?
Thanks!
From the docs:
Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction
SQLAlchemy uses a transactional unit of work model, wherein each transaction is assumed to be internally consistent. A session is an interface on top of a transaction. Since a transaction is assumed to be internally consistent, SQLAlchemy will only (well, not quite, but for ease of explanation...) retrieve a given piece of data from the database and update the state of the associated objects once per transaction. Since you already queried for the object in the same session transaction, SQLAlchemy will not update the data in that object from the database again within that transaction scope. If you want to poll the database, you'll need to do it with a fresh transaction each time.
session.refresh() didn't work for me either. Even though I saw a low-level SELECT the object was not updated after the refresh.
This answer https://stackoverflow.com/a/11121788/562267 hints to doing an actual commit/rollback to reset the session, and that worked for me:
user_1 = session.query(User).filter(User.id==1).one()
user_1.name # This prints: u'user1'
# update the database from another client here
session.commit()
user_1 = session.query(User).filter(User.id==1).one()
user_1.name # Should be updated now.
Did you try with "expire" as described in the official doc:
http://docs.sqlalchemy.org/en/rel_0_8/orm/session.html#refreshing-expiring
# expire objects obj1, obj2, attributes will be reloaded
# on the next access:
session.expire(user_1)
session.refresh(user_1)
Using expire on a object results in a reload that will occur upon next access.
Merge the session.
u = session.query(User).get(id)
u.name = 'user1_changed'
u = session.merge(u)
This will update the database and return the newer object.