fix: resolve get_database_schema resource validation errors

[shitalm]

Problem

The get_database_schema resource was failing with query validation errors:

1. SQL query used ::regclass which only works for tables/materialized views, not regular views
2. obj_description function was not in SafeSqlDriver's allowed functions list, causing validation failures

Solution

• Updated SQL query in database_resources.py to use pg_class directly via LEFT JOINs instead of ::regclass
  • Works for all table types: tables, views, and materialized views
  • Uses proper schema matching with pg_namespace and pg_class
• Added obj_description, col_description, and shobj_description to SafeSqlDriver allowed functions
  • These are safe read-only functions needed for retrieving object comments
  • Required for the schema resource to work correctly

Changes

• src/postgres_mcp/resources/database_resources.py: Fixed SQL query to handle all table types
• src/postgres_mcp/sql/safe_sql.py: Added description functions to allowed functions list

Testing

• get_database_schema resource now works correctly for databases with tables and views
• No more 'Error validating query' messages when accessing database://schema resource

[neverinfamous]

Thank you so much for this excellent contribution, @shitalm! 🎉

This fix addresses a real issue that was causing the database://schema resource to fail when databases contain views. Your solution is clean and well-implemented:

✅ Smart Query Refactoring: Using pg_class with LEFT JOINs instead of ::regclass ensures compatibility with all table types (tables, views, and materialized views)

✅ Security-Conscious: Adding the description functions (obj_description, col_description, shobj_description) to the SafeSqlDriver allowed list maintains security while enabling proper functionality

✅ Well-Documented: Clear explanation of the problem and solution in your PR description

This is exactly the kind of quality contribution that makes open source great. The fix has been merged and will be included in the next release.

Thanks again for taking the time to identify and fix this issue! 🙏