fix: resolve get_database_schema resource validation errors (#22)

Fixes SQL query validation errors when accessing database://schema resource with views.

- Fixed SQL query to use pg_class directly via LEFT JOINs instead of ::regclass
- Added obj_description, col_description, and shobj_description to SafeSqlDriver allowed functions
- Ensures database://schema resource works correctly with tables, views, and materialized views

Co-authored-by: shitalm <[email protected]>

Author: shitalm

src/postgres_mcp/resources/database_resources.py

@@ -35,13 +35,16 @@ async def get_database_schema() -> str:  # pyright: ignore[reportUnusedFunction]
             sql_driver: Any = await get_sql_driver_func()
 
             # Query information_schema for tables
+            # Use pg_class directly to avoid ::regclass issues with views
             tables_query = """
                 SELECT
                     t.table_schema,
                     t.table_name,
                     t.table_type,
-                    obj_description((t.table_schema||'.'||t.table_name)::regclass) as table_comment
+                    obj_description(c.oid, 'pg_class') as table_comment
                 FROM information_schema.tables t
+                LEFT JOIN pg_namespace n ON n.nspname = t.table_schema
+                LEFT JOIN pg_class c ON c.relnamespace = n.oid AND c.relname = t.table_name
                 WHERE t.table_schema NOT IN ('pg_catalog', 'information_schema')
                 ORDER BY t.table_schema, t.table_name
             """

src/postgres_mcp/sql/safe_sql.py

@@ -306,6 +306,9 @@ class SafeSqlDriver(SqlDriver):
         "unicode_version",
         "icu_unicode_version",
         # Database object information functions
+        "obj_description",
+        "col_description",
+        "shobj_description",
         "pg_column_size",
         "pg_column_compression",
         "pg_column_toast_chunk_id",