revert: restore db2.py and connection.py to 003593b state (37 passing baseline)

Author: iawanish

sqlmesh/core/config/connection.py

@@ -2650,15 +2650,8 @@ def _engine_adapter(self) -> t.Type[EngineAdapter]:
         )
 
     def get_catalog(self) -> t.Optional[str]:
-        """
-        Return the catalog (database) name uppercased.  Db2 stores all unquoted
-        identifiers in uppercase and CURRENT SERVER returns an uppercase string.
-        get_current_catalog() also returns uppercase, so _default_catalog and the
-        live catalog value are always in the same case.  The set_catalog() decorator's
-        REQUIRES_SET_CATALOG path compares catalog_name != get_current_catalog(); a
-        case mismatch (e.g. duckdb-dialect lowercase "testdb" vs "TESTDB") triggers
-        set_current_catalog() which is a no-op — so both cases are handled safely.
-        """
+        """Db2 stores catalog names in uppercase; normalise here so the default_catalog
+        passed to the adapter matches what get_current_catalog() returns at runtime."""
         catalog = super().get_catalog()
         return catalog.upper() if catalog else None
 

sqlmesh/core/engine_adapter/db2.py

@@ -85,12 +85,7 @@ class Db2EngineAdapter(
     def get_current_catalog(self) -> t.Optional[str]:
         """
         Db2 requires FROM SYSIBM.SYSDUMMY1 to read the CURRENT SERVER special register.
-        Returns the value uppercased to match the convention used by _default_catalog
-        (which comes from get_catalog() → database name as supplied in config, uppercased).
-        The set_catalog() decorator's REQUIRES_SET_CATALOG path compares
-        catalog_name != get_current_catalog() — normalising both to uppercase ensures
-        the comparison is consistent regardless of which dialect (db2 UPPERCASE vs
-        duckdb LOWERCASE) produced the catalog token in the model expression.
+        Returns uppercase to match the Db2 dialect's identifier normalisation.
         """
         result = self.fetchone("SELECT CURRENT SERVER FROM SYSIBM.SYSDUMMY1")
         if result:
@@ -331,19 +326,7 @@ def _db2_type_to_sqlglot(self, db2_type: str, length: int, scale: int) -> exp.Da
 
     @property
     def catalog_support(self) -> CatalogSupport:
-        # REQUIRES_SET_CATALOG is used instead of SINGLE_CATALOG_ONLY because the
-        # SINGLE_CATALOG_ONLY path in set_catalog() (shared.py:346) does a raw ==
-        # comparison between catalog_name and _default_catalog.  catalog_name comes
-        # from the model expression, whose case depends on the dialect that built it:
-        # db2 dialect → UPPERCASE, duckdb dialect → lowercase.  Either case can appear
-        # at runtime and we cannot control which, so a raw == would fail for one case.
-        #
-        # The REQUIRES_SET_CATALOG path instead calls get_current_catalog() for the
-        # right-hand side.  By returning uppercase from both get_catalog() (connection.py)
-        # and get_current_catalog(), and by making set_current_catalog() a no-op (Db2 has
-        # only one catalog — CONNECT TO cannot change it meaningfully), the mismatch is
-        # tolerated: lowercase "testdb" != "TESTDB" → set_current_catalog (no-op) → proceed.
-        return CatalogSupport.REQUIRES_SET_CATALOG
+        return CatalogSupport.SINGLE_CATALOG_ONLY
 
     def table_exists(self, table_name: TableName) -> bool:
         """
@@ -851,18 +834,9 @@ def _df_to_source_queries(
         )
 
     def set_current_catalog(self, catalog: str) -> None:
-        """
-        No-op for Db2 — there is only one catalog (the database name) and CONNECT TO
-        cannot switch to a different one in the middle of a session.  The set_catalog()
-        decorator calls this when catalog_name != get_current_catalog(), which happens
-        because model expressions built through a duckdb-dialect context carry lowercase
-        catalog names while get_current_catalog() returns uppercase.  The mismatch is
-        case-only and harmless, so we log it and return without executing any SQL.
-        """
-        logger.debug(
-            "set_current_catalog called with %r — no-op for Db2 (single-catalog engine)",
-            catalog,
-        )
+        """Switches the active catalog using Db2's CONNECT TO statement."""
+        self.execute(f"CONNECT TO {catalog}")
+        logger.debug("Switched to catalog: %s", catalog)
 
     @cached_property
     def server_version(self) -> t.Tuple[int, int]: