Python OOP: how to share a MongoDB connection with all classes

Question

I'm working on a Python OOP project. I have to deal with MongoDB interaction but I don't want to use an ODM like mongoengine.

What I want is to share a main Mongo connection with all classes that have to interact with it. I think that using a main DB class could be a good idea and I have two solutions in mind.

Solution A Connection at class level

mydb.py

from pymongo import MongoClient

class MyMongoDB(object):

    _client = MongoClient('localhost', 27017)
    db = _client['name_of_the_db']

And in other classes:

from mydb import MyMongoDB

class Foo(object):

    _db_collection = MyMongoDB.db.foo_collection

    def __init__(self):
       pass

    def set_data(self, data):
       Foo._db_collection.insert_one(data)

Solution A Connection at instance level

mydb.py

from pymongo import MongoClient

class MyMongoDB(object):

    def __init__(self):
        _client = MongoClient('localhost', 27017)
        db = _client['name_of_the_db']

And in other classes:

from mydb import MyMongoDB

class Foo(object):

    _db_collection = MyMongoDB().db.foo_collection

    def __init__(self):
       pass

    def set_data(self, data):
       Foo._db_collection.insert_one(data)

In solution A I have one main connection even if I import the MongoDB class in a lot of modules.

In solution B I have one new instance for each import

I think that solution A is the proper way to do the trick. Isn't it? Are they better approaches?

Answer 1

Python makes this simple. Have a module-level global variable:

client = MongoClient()

If that's in a module like "my_db.py" then elsewhere you can access the client like this:

from my_db import client

There's various bigotries against global variables in other programming languages, but in Python it's the simplest way to share an object throughout your program.