Determine whether collection in MongoDB exists in Python

Question

I want to know whether collections of specific names exists in the MongoDB. How can I achieve this programmatically in Python. On searching about the same, I got to know how to do that from MongoDB shell but nothing useful for doing the same in Python.

Possible duplicate of [How to check in PyMongo if collection exists and if exists empty (remove all from collection)?](http://stackoverflow.com/questions/9822575/how-to-check-in-pymongo-if-collection-exists-and-if-exists-empty-remove-all-fro) — Alex, Dec 09 '15 at 15:53
@Alex : Can you please post this as answer so that I can accept this as final answer? — POOJA GUPTA, Dec 09 '15 at 16:57

MehmedB · Answer 1 · 2022-10-14T07:30:45.827

You can use the method to retrieve and check if your collection exists or not from the comment given by the @Alex like this:

Method 1:

import pymongo

connection = pymongo.MongoClient('localhost', 27017)  # Connect to mongodb

db = connection['test_db']
list_of_collections = db.list_collection_names()  # Return a list of collections in 'test_db'
print("posts" in list_of_collections)  # Check if collection "posts" exists in db (test_db)

Or, you can validate a collection with validate_collection() (documentation) This returns an error (pymongo.errors.OperationFailure) if the collection doesn't exist. With this method, you can also catch that exception and do whatever you want.

Method 2:

import pymongo
connection = pymongo.MongoClient('localhost', 27017)  # Connect to mongodb

db = connection['test_db']

try:
    db.validate_collection("random_collection_name")  # Try to validate a collection
except pymongo.errors.OperationFailure:  # If the collection doesn't exist
    print("This collection doesn't exist")

I really prefer the second Method, especially since it also allows you to see if a collection is actually a collection or a view, since list_collection_names() also returns views. — Thomas J, Aug 18 '22 at 13:44
if you're getting `pymongo.errors.OperationFailure: user is not allowed to do action [validate]` change role to `Admin` — Bn.F76, Dec 09 '22 at 00:42
Doesn't work as expected... The OperationFailure exception does not occur. — Eduardo Lucio, Aug 10 '23 at 19:55

score 0 · Answer 2 · answered Aug 10 '23 at 20:02

A more complete approach testing connection, database and collection.

Thanks!

#!/usr/bin/python

from pymongo import MongoClient
from pymongo.errors import PyMongoError


def connect_to_mongodb(conn_str: str, database: str, collection: str):
    """Opens the connection to MongoDB."""

    try:
        mongo_client: MongoClient = MongoClient(conn_str)

        # NOTE: The ismaster command is cheap and does not require auth. Useful to
        # test if the connection is valid.
        mongo_client.admin.command("ismaster")

        # NOTE: Test if the base date is valid.
        if database not in mongo_client.list_database_names():
            raise PyMongoError("Invalid data base!")

        # NOTE: Test if the collection is valid.
        if collection not in mongo_client[database].list_collection_names():
            raise PyMongoError("Invalid collection!")

    except PyMongoError as e:
        print("Connection to MongoDB failed. Cause: %s" % (e))

Determine whether collection in MongoDB exists in Python

2 Answers2