[Research] Find Python 3 Compatible Replacement for MongoKit

[mcdonnnj]

This project currently relies on the MongoKit package to provide ODM functionality. That project was never made Python 3 compatible, nor was it updated for later versions of PyMongo. As it is now archived, that is likely to never happen. A suitable replacement needs to be picked to replace it, and the code in this repository updated, so that Python 3 migration can progress.

A compare and contrast needs to be done between options like MongoKat and the projects listed in the MongoDB tools page. It would be ideal if it operated in a fashion similar to MongoKit while still retaining similar features to ease the transition.

[mcdonnnj]

Rough Comparisons

MongoKit (what we use now)

• Readily exposes the underlying PyMongo object.
• Does not add fields of its own to documents.
• Override save() method to apply changes when saving a document.

PyMODM

• Does not freely expose underlying PyMongo object, but does support raw queries.
• Adds a _cls field for inheritence in the same collection, but might to be disable-able through the final metadata attribute.
• Will need to set the collection_name metadata attribute of each Document model to set the collection name to use.
• Implement abstract method clean() to apply changes when saving a document.
• Will need to make a custom QuerySet.
• Queries should be restructured to fit the PyMODM design.
• Use of exceptions instead of returning None for some search methods.

uMongo

• Readily exposes the underlying PyMongo object.
• Adds a _cls field to track model inheritence, may be configurable with the is_child metadata attribute.
• Will need to set the collection_name metadata attribute of each Document model to set the collection name to use.
• Changes when saving may be doable through pre_insert()/pre_update() methods?

MongoEngine

• Does not freely expose underlying PyMongo object, but does support raw queries.
• Adds a _cls field for inheritence in the same collection, but appears to be disableable through the allow_inheritance metadata attribute.
• Will need to set the collection metadata attribute of each Document model to set the collection name to use.
• Implement clean() method to apply changes when saving a document.
• Will need to make a custom QuerySet.
• Queries should be restructured to fit the MongoEngine design.
• Possible migration issues if a field is added to a document's schema.
• Use of exceptions instead of returning None for some search methods.

[mcdonnnj]

After discussion, the similarities of PyMODM and MongoEngine left the main argument down to support. The pause of PyMODM maintenance per this forum post was a major reason to side with MongoEngine.

[mcdonnnj]

We moved on to discussing whether the transition to Python 3 should happen simultaneously with the transition to MongoEngine. We decided to switch to MongoEngine first, and then work on the transition to Python 3 after for the following reasons:

• The last release of MongoEngine that supported Python 2 was v0.19.1 in 2020-01-04, so it is relatively recent.
• It is easier to add a Python 3 migration mid-stream if necessary than to decouple a Python 3 migration mid-stream.
• Given how interconnected the code in this repository is, and the number of other projects that rely on it, it is a saner approach to transition to Python 3 after a MongoEngine transition.

[mcdonnnj]

Tracking migration to the chosen ODM will take place in #54.