feat: add example showing how to open an existing ObjectBox database

[ElizioMartins]

Problem

Issue #20 (open since May 2024) shows that many users don't realize ObjectBox opens an existing database transparently — there is no special "open" API. When Store(directory=\"...\") is called and the directory already contains a data.mdb file, ObjectBox simply opens it. This confused users who thought they needed a separate API call.

Solution

Added a new minimal example (example/open-existing-db/) that demonstrates this behavior in three clear steps:

# Step 1: create the database and write data
python main.py write

# Step 2: open the SAME directory — ObjectBox opens the existing DB automatically
python main.py read

# Step 3: reset to start fresh
python main.py reset

The example also mentions the cross-platform use case (reading a database created by another ObjectBox SDK), which was the underlying motivation in the issue thread.

Files changed

• example/open-existing-db/main.py — new self-contained example
• example/README.md — added the new example to the list with description and sample output

Closes #20

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About the contributor: I'm a developer passionate about open source and always looking for opportunities to contribute and grow. If you're looking for collaborators or have open positions, feel free to reach out!

• 🔗 LinkedIn: https://www.linkedin.com/in/elizio-martins/
• 📧 E-mail: elizio.matins@gmail.com