We Keep Coding

In python flask with mysql, can I use the same connection throught the app life cycle?

Here is my python flask code:
from flask import *
import mysql.connector
app = Flask(__name__)
conn = mysql.connector.connect(
host="<my db host>",
user="<my db user>",
password = "<my db password>",
database = '<my db>'
)
#app.route('/posts/<int:post_id>')
def get_post(post_id):
with conn.cursor(dictionary=True) as cur:
cur.execute('select * from posts where ID=%s',(post_id,))
result = cur.fetchone()
ans=result['post_content']
return ans
app.run(debug=False,threaded=True,host='0.0.0.0',port=80)
Note how I don't create a new connection for each request. Instead, I use the same connection for all requests.
My question is: is there any potential problems in this approach?

You should not use the same connection, because it will stay open forever, only open an SQL connection when you need to use it, and close it afterward. Not doing so can lead to a lot of errors.

SQLAlchemy keeps the DB connection open

I have an issue with in my Flask app concerning SQLAlchemy and MySQL.
In one of my file: connection.py I have a function that creates a DB connection and set it as a global variable:
db = None
def db_connect(force=False):
global db
db = pymysql.connect(.....)
def makecursor():
cursor = db.cursor(pymysql.cursors.DictCursor)
return db, cursor
And then I have a User Model created with SQL ALchemy models.ppy
class User(Model):
id = column........
It inherits from Model which is a class that I create in another file orm.py
import connection
Engine = create_engine(url, creator=lambda x: connection.makecursor()[0], pool_pre_ping=True)
session_factory = sessionmaker(bind=Engine, autoflush=autoflush)
Session = scoped_session(session_factory)
class _Model:
query = Session.query_property()
Model = declarative_base(cls=_Model, constructor=model_constructor)
In my application I can have long script running so the DB timeout. So I have a function that "reconnect" my DB (it actually only create a new connexion and replace the global DB variable)
My goal is to be able to catch the close of my DB and reconnect it instantly. I tried with SQLAlchemy events but it never worked. (here)
Here is some line that reproduces the error:
res = User.query.filter_by(username="myuser#gmail.com").first()
connection.db.close()
# connection.reconnect() # --> SOLUTION
res = User.query.filter_by(username="myuser#gmail.com").first()
If you guys have any ideas of how to achieve that, let me know 🙏🏻
Oh and I forgot, this application is still running with python2.7.

How to use multiple Mongodb in flask

I have two mysql database one is localhost and another is in server now, am going to create simple app in python using flask for that application i would like to connect the both mysql DB (local and server).
Any one please suggest how to connect multiple DB into flask.
app = Flask(__name__)
client = MongoClient()
client = MongoClient('localhost', 27017)
db = client.sampleDB1
Sample code if possible.
Thanks

I had the same issue, finally figured it out.
Instead of using
client = MongoClient()
client = MongoClient('localhost', 27017)
db = client.sampleDB1
Delete all that and try this:
mongo1 = PyMongo(app, uri = 'mongodb://localhost:27017/Database1')
mongo2 = PyMongo(app, uri = 'mongodb://localhost:27017/Database2')
Then, when you want to call a particular database you can use:
#app.route('/routenamedb1', methods=['GET'])
def get_data_from_Database1():
Database1 = mongo1.db.CollectionName ##Notice I use mongo1,
#If I wanted to access database2 I would use mongo2
#Walk through the Database for DC to
for s in Database1.find():
#Modifying code
return data

#This technique can be used to connect to multiple databases or database servers:
app = Flask(__name__)
# connect to MongoDB with the defaults
mongo1 = PyMongo(app)
# connect to another MongoDB database on the same host
app.config['MONGO2_DBNAME'] = 'dbname_two'
mongo2 = PyMongo(app, config_prefix='MONGO2')
# connect to another MongoDB server altogether
app.config['MONGO3_HOST'] = 'another.host.example.com'
app.config['MONGO3_PORT'] = 27017
app.config['MONGO3_DBNAME'] = 'dbname_three'
mongo3 = PyMongo(app, config_prefix='MONGO3')

create model.py and separate instances of 2 databases inside it, then in app.py:
app = Flask(__name__)
app.config['MODEL'] = model.my1st_database()
app.config['MODEL2'] = model.my2nd_database()
works for me :)

How to run raw mongodb commands from pymongo

In a mongo command line I can run
db.my_collection.stats()
I need to get my collections stats from Python so I tried
from pymongo import MongoClient
client = MongoClient()
db = client.test_database
collection = db.test_collection
collection.stats()
But I get
TypeError: 'Collection' object is not callable.
If you meant to call the 'stats' method on a 'Collection' object it is failing because no such method exists.
This is because pymongo does not support this method. How do I send raw mongoDB commands to mongo through Python?

from pymongo import MongoClient
client = MongoClient()
db = client.test_database
print(db.command("collstats", "test_collection"))

Approach 1 with PyMongo:
client = pymongo.MongoClient(host = "127.0.0.1", port = 27017)
db = client.test_database
db.command("dbstats") # prints database stats for "test_db"
db.command("collstats", "test_collection") # prints collection-level stats
This can be done with this approach in Django.
from django.db import connections
database_wrapper = connections['my_db_alias']
eggs_collection = database_wrapper.get_collection('eggs')
eggs_collection.find_and_modify(...)
From django-mongodb-engine docs:
django.db.connections is a dictionary-like object that holds all
database connections – that is, for MongoDB databases,
django_mongodb_engine.base.DatabaseWrapper instances.
These instances can be used to get the PyMongo-level Connection,
Database and Collection objects.

How do I connect as sysdba for oracle db using SQLALchemy

I am using sqlalchemy with flask
and I want to connect to oracle DB as sysdba
SQLALCHEMY_DATABASE_URI ='oracle+cx_oracle://sys:abc#DBNAME[mode=SYSDBA]'
This doesnt work and gives me a
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config.from_object('config')
db = SQLAlchemy(app)
from app import views,models
and I use this db object later. But I am not able to figure out how to write the
SQLALCHEMY_DATABASE_URI to login as sysdba
I also tried
CONN = cx_Oracle.connect('sys/abc', dsn='DBNAME', mode = cx_Oracle.SYSDBA)
SQLALCHEMY_DATABASE_URI = CONN
But that also doesnt work.
I get ORA-12154: TNS: could not resolve the connect identifier specified” .. also If I remove mode=SYSDBA I get ORA-28009 connection as SYS should be as SYSDBA

Your dsn parameter is wrong. You must also separate the user and password parameters. Try this (it's working for me):
dsn_tns = cx_Oracle.makedsn('host', port, 'sid')
CONN = cx_Oracle.connect('sys', 'abc', dsn_tns, mode=cx_Oracle.SYSDBA)
For more info see cx_Oracle.connect constructor.