fix(mssql): update driver selection logic to allow enforcing pyodbc in Fabric

Author: mattiasthalen

sqlmesh/core/config/connection.py

@@ -1510,7 +1510,14 @@ def _mssql_engine_import_validator(cls, data: t.Any) -> t.Any:
         if not isinstance(data, dict):
             return data
 
-        driver = data.get("driver", "pymssql")
+        # Get the default driver for this specific class
+        default_driver = "pymssql"
+        if hasattr(cls, "model_fields") and "driver" in cls.model_fields:
+            field_info = cls.model_fields["driver"]
+            if hasattr(field_info, "default") and field_info.default is not None:
+                default_driver = field_info.default
+
+        driver = data.get("driver", default_driver)
 
         # Define the mapping of driver to import module and extra name
         driver_configs = {"pymssql": ("pymssql", "mssql"), "pyodbc": ("pyodbc", "mssql-odbc")}

tests/core/test_connection_config.py

@@ -1766,3 +1766,50 @@ def test_fabric_pyodbc_connection_string_generation():
 
         # Check autocommit parameter, should default to True for Fabric
         assert call_args[1]["autocommit"] is True
+
+
+def test_mssql_driver_defaults(make_config):
+    """Test driver defaults for MSSQL connection config.
+
+    Ensures MSSQL defaults to 'pymssql' but can be overridden to 'pyodbc'.
+    """
+
+    # Test 1: MSSQL with no driver specified - should default to pymssql
+    config_no_driver = make_config(type="mssql", host="localhost", check_import=False)
+    assert isinstance(config_no_driver, MSSQLConnectionConfig)
+    assert config_no_driver.driver == "pymssql"
+
+    # Test 2: MSSQL with explicit pymssql driver
+    config_pymssql = make_config(
+        type="mssql", host="localhost", driver="pymssql", check_import=False
+    )
+    assert isinstance(config_pymssql, MSSQLConnectionConfig)
+    assert config_pymssql.driver == "pymssql"
+
+    # Test 3: MSSQL with explicit pyodbc driver
+    config_pyodbc = make_config(type="mssql", host="localhost", driver="pyodbc", check_import=False)
+    assert isinstance(config_pyodbc, MSSQLConnectionConfig)
+    assert config_pyodbc.driver == "pyodbc"
+
+
+def test_fabric_driver_defaults(make_config):
+    """Test driver defaults for Fabric connection config.
+
+    Ensures Fabric defaults to 'pyodbc' and cannot be changed to 'pymssql'.
+    """
+
+    # Test 1: Fabric with no driver specified - should default to pyodbc
+    config_no_driver = make_config(type="fabric", host="localhost", check_import=False)
+    assert isinstance(config_no_driver, FabricConnectionConfig)
+    assert config_no_driver.driver == "pyodbc"
+
+    # Test 2: Fabric with explicit pyodbc driver
+    config_pyodbc = make_config(
+        type="fabric", host="localhost", driver="pyodbc", check_import=False
+    )
+    assert isinstance(config_pyodbc, FabricConnectionConfig)
+    assert config_pyodbc.driver == "pyodbc"
+
+    # Test 3: Fabric with pymssql driver should fail (not allowed)
+    with pytest.raises(ConfigError, match=r"Input should be 'pyodbc'"):
+        make_config(type="fabric", host="localhost", driver="pymssql", check_import=False)