FIX: fetchone/fetchmany/fetchall type-checking under ty (#620)

[gargsaumya]

Work Item / Issue Reference

AB#45498

GitHub Issue: #620

---

Summary

This pull request refactors how column name mappings are handled for catalog/metadata result sets in the mssql_python/cursor.py module, specifically to avoid dynamically reassigning fetch methods (like fetchone, fetchmany, and fetchall) as instance attributes. This change improves compatibility with static type checkers and ensures cleaner, more predictable method behavior. A regression test is also added to prevent future regressions.

Refactoring of column mapping and fetch method handling:

• Refactored the _prepare_metadata_result_set method to build and cache the column name to index map (_column_map) directly, merging in specialized aliases when provided, and removed all logic that dynamically wraps or reassigns fetch methods on the instance. This ensures fetch methods remain class methods and improves static type checking compatibility. [1] [2]
• Updated the __init__ method of the cursor to initialize the new _column_map attribute, and clarified the usage of cached column maps.
• Removed obsolete logic in execute that restored original fetch methods, since fetch methods are no longer replaced at runtime.

Testing and regression prevention:

• Added test_fetch_methods_not_shadowed_on_instance to verify that fetch methods are never shadowed as instance attributes, preventing regressions related to GH cursor.fetchall, fetchmany and fetchone fail to type-check under ty #620 and ensuring compatibility with static type checkers.

[github-actions]

📊 Code Coverage Report

🔥 Diff Coverage 87%

🎯 Overall Coverage 80%

📈 Total Lines Covered: 6666 out of 8238 📁 Project: mssql-python

---

Diff Coverage

Diff: main...HEAD, staged and unstaged changes

• mssql_python/cursor.py (87.5%): Missing lines 1641

Summary

• Total: 8 lines
• Missing: 1 line
• Coverage: 87%

mssql_python/cursor.py

Lines 1637-1645

  1637         # Some catalog helpers expose additional friendly aliases (e.g. ODBC 2.x
  1638         # vs 3.x column names) via a specialized mapping. Merge them in so they
  1639         # resolve to the same column indices.
  1640         if specialized_mapping:
! 1641             column_map.update(specialized_mapping)
  1642 
  1643         # Route the map through the shared fetch path. The standard fetchone/
  1644         # fetchmany/fetchall methods read these cached maps when constructing Row
  1645         # objects, so metadata rows pick up the catalog column names without any

---

---

📋 Files Needing Attention

📉 Files with overall lowest coverage (click to expand)

mssql_python.pybind.logger_bridge.cpp: 59.2%
mssql_python.pybind.ddbc_bindings.h: 59.9%
mssql_python.pybind.logger_bridge.hpp: 70.8%
mssql_python.pybind.ddbc_bindings.cpp: 76.3%
mssql_python.row.py: 76.9%
mssql_python.__init__.py: 77.3%
mssql_python.pybind.connection.connection.cpp: 77.3%
mssql_python.ddbc_bindings.py: 79.6%
mssql_python.logging.py: 85.5%
mssql_python.connection.py: 85.6%

---

🔗 Quick Links

⚙️ Build Summary	📋 Coverage Details
View Azure DevOps Build	Browse Full Coverage Report

[Copilot]

Pull request overview

This PR refactors how catalog/metadata result sets set up column name mappings in mssql_python/cursor.py to avoid dynamically reassigning fetchone/fetchmany/fetchall on the cursor instance (which can confuse static type checkers like ty). It also adds a regression test to ensure fetch methods are never shadowed as instance attributes.

Changes:

• Refactored _prepare_metadata_result_set to build/cache a column name → index map instead of wrapping/replacing fetch methods.
• Removed now-obsolete “restore original fetch methods” logic from execute.
• Added a regression test asserting fetch methods remain class methods (not instance attributes) across metadata helpers and normal execute.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
mssql_python/cursor.py	Stops runtime reassignment of fetch methods by routing metadata column mappings through the shared cached map path.
tests/test_004_cursor.py	Adds a regression test to prevent fetch methods being shadowed on the cursor instance (GH #620).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[sumitmsft]

approved with minor changes