diff options
Diffstat (limited to 'lib/sqlalchemy/engine')
| -rw-r--r-- | lib/sqlalchemy/engine/__init__.py | 18 | ||||
| -rw-r--r-- | lib/sqlalchemy/engine/default.py | 12 |
2 files changed, 30 insertions, 0 deletions
diff --git a/lib/sqlalchemy/engine/__init__.py b/lib/sqlalchemy/engine/__init__.py index 2a6c68d66..bd8b7e68a 100644 --- a/lib/sqlalchemy/engine/__init__.py +++ b/lib/sqlalchemy/engine/__init__.py @@ -192,6 +192,24 @@ def create_engine(*args, **kwargs): :ref:`dbengine_logging` for information on how to configure logging directly. + :param empty_in_strategy: The SQL compilation strategy to use when + rendering an IN or NOT IN expression for :meth:`.ColumnOperators.in_` + where the right-hand side + is an empty set. This is a string value that may be one of + ``static``, ``dynamic``, or ``dynamic_warn``. The ``static`` + strategy is the default, and an IN comparison to an empty set + will generate a simple false expression "1 != 1". The ``dynamic`` + strategy behaves like that of SQLAlchemy 1.1 and earlier, emitting + a false expression of the form "expr != expr", which has the effect + of evaluting to NULL in the case of a null expression. + ``dynamic_warn`` is the same as ``dynamic``, however also emits a + warning when an empty set is encountered; this because the "dynamic" + comparison is typically poorly performing on most databases. + + .. versionadded:: 1.2 Added the ``empty_in_strategy`` setting and + additionally defaulted the behavior for empty-set IN comparisons + to a static boolean expression. + :param encoding: Defaults to ``utf-8``. This is the string encoding used by SQLAlchemy for string encode/decode operations which occur within SQLAlchemy, **outside of diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py index 18c3276f8..b8c2d2845 100644 --- a/lib/sqlalchemy/engine/default.py +++ b/lib/sqlalchemy/engine/default.py @@ -178,6 +178,7 @@ class DefaultDialect(interfaces.Dialect): supports_right_nested_joins=None, case_sensitive=True, supports_native_boolean=None, + empty_in_strategy='static', label_length=None, **kwargs): if not getattr(self, 'ported_sqla_06', True): @@ -207,6 +208,17 @@ class DefaultDialect(interfaces.Dialect): self.supports_native_boolean = supports_native_boolean self.case_sensitive = case_sensitive + self.empty_in_strategy = empty_in_strategy + if empty_in_strategy == 'static': + self._use_static_in = True + elif empty_in_strategy in ('dynamic', 'dynamic_warn'): + self._use_static_in = False + self._warn_on_empty_in = empty_in_strategy == 'dynamic_warn' + else: + raise exc.ArgumentError( + "empty_in_strategy may be 'static', " + "'dynamic', or 'dynamic_warn'") + if label_length and label_length > self.max_identifier_length: raise exc.ArgumentError( "Label length of %d is greater than this dialect's" |