Fix DDL non-conditionality re SQL Server

Author: RudolfCardinal

cardinal_pythonlib/sqlalchemy/schema.py

@@ -385,9 +385,11 @@ def execute_ddl(
     Previously we would use DDL(sql, bind=engine).execute(), but this has gone
     in SQLAlchemy 2.0.
 
-    If you want dialect-conditional execution, create the DDL object with e.g.
-    ddl = DDL(sql).execute_if(dialect=SqlaDialectName.SQLSERVER), and pass that
-    DDL object to this function.
+    Note that creating the DDL object with e.g. ddl =
+    DDL(sql).execute_if(dialect=SqlaDialectName.SQLSERVER), and passing that
+    DDL object to this function, does NOT make execution condition; it executes
+    regardless. The execute_if() construct is used for listeners; see
+    https://docs.sqlalchemy.org/en/20/core/ddl.html#sqlalchemy.schema.ExecutableDDLElement.execute_if
     """
     assert bool(sql) ^ (ddl is not None)  # one or the other.
     if sql:

cardinal_pythonlib/sqlalchemy/sqlserver.py

@@ -33,6 +33,7 @@
 from sqlalchemy.schema import DDL
 
 from cardinal_pythonlib.sqlalchemy.dialect import (
+    get_dialect_name,
     quote_identifier,
     SqlaDialectName,
 )
@@ -49,7 +50,12 @@ def _exec_ddl_if_sqlserver(engine: Engine, sql: str) -> None:
     """
     Execute DDL only if we are running on Microsoft SQL Server.
     """
-    ddl = DDL(sql).execute_if(dialect=SqlaDialectName.SQLSERVER)
+    # DO NOT USE DDL(sql).execute_if(dialect=SqlaDialectName.SQLSERVER).
+    # IT IS NOT EXECUTED CONDITIONALLY VIA THIS METHOD.
+    dialect_name = get_dialect_name(engine)
+    if dialect_name != SqlaDialectName.SQLSERVER:
+        return
+    ddl = DDL(sql)
     execute_ddl(engine, ddl=ddl)
 
 

cardinal_pythonlib/sqlalchemy/tests/schema_tests.py

@@ -35,10 +35,11 @@
 from sqlalchemy.engine import create_engine
 from sqlalchemy.exc import NoSuchTableError, OperationalError
 from sqlalchemy.ext import compiler
-from sqlalchemy.orm import declarative_base
+from sqlalchemy.orm import declarative_base, Session, sessionmaker
 from sqlalchemy.schema import (
     Column,
     CreateTable,
+    DDL,
     DDLElement,
     Index,
     MetaData,
@@ -59,6 +60,10 @@
     Time,
 )
 
+from cardinal_pythonlib.sqlalchemy.engine_func import (
+    get_dialect_name,
+    SqlaDialectName,
+)
 from cardinal_pythonlib.sqlalchemy.schema import (
     add_index,
     column_creation_ddl,
@@ -98,6 +103,9 @@
     view_exists,
 )
 from cardinal_pythonlib.sqlalchemy.session import SQLITE_MEMORY_URL
+from cardinal_pythonlib.sqlalchemy.sqlserver import (
+    if_sqlserver_disable_constraints,
+)
 
 Base = declarative_base()
 log = logging.getLogger(__name__)
@@ -485,7 +493,7 @@ def test_mssql_transaction_count(self) -> None:
 
 
 class YetMoreSchemaTests(unittest.TestCase):
-    def __init__(self, *args, echo: bool = False, **kwargs) -> None:
+    def __init__(self, *args, echo: bool = True, **kwargs) -> None:
         self.echo = echo
         super().__init__(*args, **kwargs)
 
@@ -631,6 +639,69 @@ def test_execute_ddl(self) -> None:
         with self.assertRaises(AssertionError):
             execute_ddl(self.engine)  # neither
 
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    # Dialect conditionality for DDL
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    @staticmethod
+    def _present_in_log_output(_cm, msg: str) -> bool:
+        """
+        Detects whether a string is present, INCLUDING AS A SUBSTRING, in
+        log output captured from an assertLogs() context manager.
+        """
+        return any(msg in line for line in _cm.output)
+
+    def test_ddl_dialect_conditionality_1(self) -> None:
+        self.engine.echo = True  # will write to log at INFO level
+
+        # 1. Check that logging capture works, and our _present_in_log_output
+        # function.
+        with self.assertLogs(level=logging.INFO) as cm:
+            log.info("dummy call")
+            self.assertTrue(self._present_in_log_output(cm, "dummy"))
+
+        # 2. Check our dialect is as expected: SQLite.
+        dialect_name = get_dialect_name(self.engine)
+        self.assertEqual(dialect_name, SqlaDialectName.SQLITE)
+
+        # 3. Seeing if DDL built with execute_if() will execute "directly" when
+        # set to execute-if-SQLite. It executes - but not conditionally!
+        ddl_yes = DDL("CREATE TABLE yesplease (a INT)").execute_if(
+            dialect=SqlaDialectName.SQLITE
+        )
+        with self.assertLogs(level=logging.INFO) as cm:
+            execute_ddl(self.engine, ddl=ddl_yes)
+            self.assertTrue(
+                self._present_in_log_output(cm, "CREATE TABLE yesplease")
+            )
+
+        # 4. Seeing if DDL built with execute_if() will execute "directly" when
+        # set to execute-if-MySQL. It executes - therefore not conditionally!
+        # I'd misunderstood this: it is NOT conditionally executed.
+        ddl_no = DDL("CREATE TABLE nothanks (a INT)").execute_if(
+            dialect=SqlaDialectName.MYSQL
+        )
+        with self.assertLogs(level=logging.INFO) as cm:
+            execute_ddl(self.engine, ddl=ddl_no)
+            self.assertTrue(
+                self._present_in_log_output(cm, "CREATE TABLE nothanks")
+            )
+            # I'd thought this would be false, but it is true.
+
+    def test_ddl_dialect_conditionality_2(self) -> None:
+        # Therefore:
+        self.engine.echo = True  # will write to log at INFO level
+        # The test above (test_ddl_dialect_conditionality_1) proves that
+        # this code will log something if SQL is emitted.
+
+        session = sessionmaker(
+            bind=self.engine, future=True
+        )()  # type: Session
+
+        with self.assertNoLogs(level=logging.INFO):
+            with if_sqlserver_disable_constraints(session, tablename="person"):
+                pass
+            # Should do nothing, therefore emit no logs.
+
 
 class SchemaAbstractTests(unittest.TestCase):
     # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

cardinal_pythonlib/version_string.py

@@ -31,5 +31,5 @@
 
 """
 
-VERSION_STRING = "2.0.0"
+VERSION_STRING = "2.0.1"
 # Use semantic versioning: https://semver.org/

docs/source/changelog.rst

@@ -846,3 +846,9 @@ Quick links:
     was apply filters (if required) and execute.
 
   - Multiple internal changes to support SQLAlchemy 2.
+
+**2.0.1 (2025-01-22)**
+
+- Bugfix to ``cardinal_pythonlib.sqlalchemy.sqlserver`` functions as they
+  were executing unconditionally, regardless of SQLAlchemy dialect (they should
+  have been conditional to SQL Server).