MongoDB/NoSQL: Keeping Document Change History

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A fairly common requirement in database applications is to track changes to one or more specific entities in a database. I've heard this called row versioning, a log table or a history table (I'm sure there are other names for it). There are a number of ways to approach it in an RDBMS--you can write all changes from all source tables to a single table (more of a log) or have a separate history table for each source table. You also have the option to either manage the logging in application code or via database triggers.

I'm trying to think through what a solution to the same problem would look like in a NoSQL/document database (specifically MongoDB), and how it would be solved in a uniform way. Would it be as simple as creating version numbers for documents, and never overwriting them? Creating separate collections for "real" vs. "logged" documents? How would this affect querying and performance?

Anyway, is this a common scenario with NoSQL databases, and if so, is there a common solution?

mongodb nosql
5 Answers

For users of Python (python 3+, and up of course) , there's HistoricalCollection that's an extension of pymongo's Collection object.

Example from the docs:

from historical_collection.historical import HistoricalCollection
from pymongo import MongoClient
class Users(HistoricalCollection):
    PK_FIELDS = ['username', ]  # <<= This is the only requirement

# ...

users = Users(database=db)

users.patch_one({"username": "darth_later", "email": "darthlater@example.com"})
users.patch_one({"username": "darth_later", "email": "darthlater@example.com", "laser_sword_color": "red"})

list(users.revisions({"username": "darth_later"}))

# [{'_id': ObjectId('5d98c3385d8edadaf0bb845b'),
#   'username': 'darth_later',
#   'email': 'darthlater@example.com',
#   '_revision_metadata': None},
#  {'_id': ObjectId('5d98c3385d8edadaf0bb845b'),
#   'username': 'darth_later',
#   'email': 'darthlater@example.com',
#   '_revision_metadata': None,
#   'laser_sword_color': 'red'}]

Full disclosure, I am the package author. :)

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