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findoneandupdate is a method in MongoDB that allows users to update a single document and retrieve its original form, all in a single atomic operation. To use findoneandupdate for MongoDB reads and writes to occur at the same time, follow these steps:

1. Connect to the MongoDB database using a client such as pymongo.

2. Select the collection in which you want to update and read the document.

3. Define the filter parameter to specify the document to be updated.

4. Define the update parameter to specify the changes to be made to the document.

5. Set the return_document parameter to 'Before' to retrieve the original document before the update.

6. Set the upsert parameter to 'True' to create a new document if the filter does not match any existing documents.

Example:

import pymongo

client = pymongo.MongoClient('mongodb://localhost:27017/')
db = client['my_database']
collection = db['my_collection']

filter = {'_id': 123}
update = {'$set': {'status': 'completed'}}
doc = collection.find_one_and_update(filter, update, return_document='Before', upsert=True)

print(doc)

In this example, we are updating a document with _id equal to 123, setting its status field to 'completed' and retrieving its original form before the update. If the document does not exist, a new document will be created with _id equal to 123 and status equal to 'completed'.