Fix RecursionError with psycopg when DEBUG=True

[goodtune]

Summary

Fixes RecursionError that occurs when using psycopg3 driver with DEBUG=True. The bug was caused by Django's SQL debug logging triggering psycopg3's mogrify operation, which opens fresh cursors that re-enter our _cursor() method, causing infinite recursion during search_path setting.

Changes

• ContextVar Guard: Prevents recursion during search_path operations
• Parameterized Queries: Uses set_config() with parameters instead of raw SQL formatting
• Smart Caching: Only sets search_path when tenant configuration actually changes
• Mogrify Optimization: Skips unnecessary mogrify calls for parameterless queries
• Isolated Unit Tests: Mock-based tests safe for parallel execution without DB operations
• Single Integration Test: Real database test with proper cleanup for end-to-end validation

Test Plan

• All existing tests continue to pass
• New isolated unit tests verify recursion prevention and caching behavior
• Tests use mock tenants to avoid DB schema creation and constraint violations
• Single integration test validates end-to-end functionality with real tenant
• Tests are thread-safe and suitable for parallel CI execution
• Compatible with both psycopg2 and psycopg3

Compatibility

• ✅ Backward compatible - no API changes
• ✅ Works with both psycopg2 and psycopg3
• ✅ No configuration required
• ✅ Transparent to consuming applications

[goodtune]

All three feedback points have been addressed:

1. Settings modification in test setup - Fixed by replacing direct settings modification with proper @override_settings decorator to prevent test isolation issues.

2. getattr fallback pattern clarity - Improved with explicit comments explaining when cursor_for_search_path would have a cursor attribute (psycopg2) vs when it wouldn't (psycopg3), and replaced getattr with explicit hasattr check for better readability.

3. Parameter check explicitness - Made the condition more explicit by changing if not params to if params is None or len(params) == 0 for clearer intent.

All tests continue to pass with both psycopg2 and psycopg3 drivers after these improvements.

[goodtune]

Addressed the additional code quality feedback from the latest review:

1. Complex boolean expression - Extracted into well-named _should_set_search_path helper method with clear documentation explaining when search_path needs to be set.

2. Cursor compatibility logic - Extracted into _get_raw_cursor helper method to improve testability and reduce complexity in the main flow.

3. & 4. Fragile inheritance references - Replaced __bases__[0] usage with explicit parent class references using django.db.utils.load_backend for robustness against inheritance changes.

These refactoring improvements enhance code maintainability and testability while preserving full functionality across both psycopg2 and psycopg3 drivers.

[Copilot]

Pull Request Overview

This PR fixes a RecursionError that occurs when using the psycopg3 PostgreSQL driver with Django's DEBUG=True setting. The bug was caused by Django's SQL debug logging triggering psycopg3's mogrify operation, which opens fresh cursors that re-enter the _cursor() method during search_path setting, creating infinite recursion.

• Implements ContextVar-based recursion prevention during search_path operations
• Switches from raw SQL formatting to parameterized queries using set_config()
• Adds smart caching to avoid redundant search_path operations
• Optimizes last_executed_query to skip unnecessary mogrify calls

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/tenant_schemas/postgresql_backend/base.py	Core fix implementing recursion prevention, parameterized queries, and caching optimizations
src/tenant_schemas/tests/test_psycopg3_recursion.py	Comprehensive test suite covering recursion prevention and caching behavior
src/tenant_schemas/tests/testcases.py	Refactors test settings management using @override_settings decorator
src/tenant_schemas/tests/test_tenants.py	Updates test classes to use @override_settings instead of direct settings modification
src/tenant_schemas/tests/test_routes.py	Removes redundant settings configuration
src/tenant_schemas/tests/test_apps.py	Fixes f-string formatting in warning message
src/tenant_schemas/apps.py	Fixes f-string formatting in warning message
dts_test_project/dts_test_app/migrations/*.py	Removes unused imports

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[goodtune]

Addressed the final round of performance and robustness feedback:

1. & 2. Backend loading inefficiency - Added class-level backend cache to avoid repeated Django backend loading in test methods, improving test performance.

3. Potential exception with len(params) - Replaced the potentially fragile params check with the more robust not params condition that safely handles all falsy values and different container types without risk of exceptions.

These optimizations improve both performance and code robustness while maintaining full functionality across both PostgreSQL drivers.