feat: Add MongoDB Connector Support

[ReginaldErzoah]

Summary

Add MongoDB connector support to Dift.

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Motivation

Dift currently supports local files, SQL databases, and warehouse-style connectors.

MongoDB support would expand Dift into NoSQL and document database workflows, enabling users to compare document collections across environments.

This is useful for:

• production vs staging collection comparison
• document schema drift detection
• NoSQL data validation
• JSON-like dataset comparison
• application data regression testing

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Proposed Improvements

• Add MongoDB URI support
• Add MongoDB collection reader
• Load MongoDB documents into a comparable format
• Integrate MongoDB with the reader registry system
• Provide helpful dependency and connection errors

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Suggested Files

Potential implementation areas:

dift/io/mongodb_reader.py
dift/io/readers.py
dift/io/registry.py
dift/io/base_reader.py
tests/test_mongodb_reader.py
docs/connectors/mongodb.md

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Suggested Tasks

• Add MongoDB URI detection
• Add MongoDB collection parsing
• Add MongoDB reader implementation
• Register MongoDB reader in the reader registry
• Add dependency guidance for MongoDB support
• Add tests
• Update documentation

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How to Test

Install MongoDB driver:

pip install pymongo

Run:

pytest
ruff check .

Run targeted tests:

pytest tests/test_mongodb_reader.py

Manual validation example:

dift mongodb://localhost:27017/app.users_old \
     mongodb://localhost:27017/app.users_new \
     --key user_id

Verify:

• MongoDB URIs are routed to the MongoDB reader
• collections load successfully
• helpful errors appear for missing drivers
• existing file, SQL, DuckDB, and BigQuery workflows remain stable

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Documentation Impact

Create:

docs/connectors/mongodb.md

Update:

docs/connectors/index.md
docs/roadmap.md
mkdocs.yml

Documentation should include:

• MongoDB URI format
• dependency installation
• collection comparison examples
• authentication guidance
• limitations and caveats

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Acceptance Criteria

• MongoDB connector exists
• MongoDB collections can be loaded for comparison
• Reader registry routes MongoDB URIs correctly
• Tests pass
• Documentation updated