feature/auto-create-new-session
Merge https://github.com/google/adk-python/pull/4072
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### Link to Issue or Description of Change
**2. Or, if no issue exists, describe the change:**
**Problem:**
When building frontend applications with ADK, there's a limitation where frontends cannot always guarantee that `create_session` is called before initiating a conversation. This creates friction in the user experience because:
- Users may refresh the page or navigate directly to a conversation URL with a specific session_id
- Frontend state management may lose track of whether a session was already created
- Mobile apps or single-page applications have complex lifecycle management where ensuring `create_session` is called first adds unnecessary complexity
- This forces developers to implement additional logic to check session existence before every conversation
Currently, if `get_session` is called with a non-existent session_id, it returns `None`, requiring the frontend to explicitly handle this case and call `create_session` separately.
**Solution:**
Modified the `get_session` method in `DatabaseSessionService` to automatically create a session if it doesn't exist in the database. This "get or create" pattern is common in many frameworks and provides a more developer-friendly API.
The implementation:
1. Attempts to fetch the session from the database
2. If the session doesn't exist (returns `None`), automatically calls `create_session` with the provided parameters
3. Retrieves and returns the newly created session
4. Maintains backward compatibility - existing code continues to work without changes
This allows frontends to simply call `get_session` with a session_id and be confident that the session will be available, regardless of whether it was previously created.
**Benefits:**
- Simplifies frontend integration by removing the need to track session creation state
- Reduces API calls (no need to check existence before calling get_session)
- Follows the principle of least surprise - getting a session with an ID should work reliably
- No breaking changes to existing code that checks for `None` return values
### Testing Plan
**Unit Tests:**
- [x] I have added or updated unit tests for my change.
- [x] All unit tests pass locally.
**pytest results:**
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/4072 from lwangverizon:feature/auto-create-new-session 5475c6ae91d12332598d521302736eb1db79a8be
PiperOrigin-RevId: 856019482
