Emit v2.0 deprecation warning for "implicit autocommit"

"Implicit autocommit", which is the COMMIT that occurs when a DML or DDL
statement is emitted on a connection, is deprecated and won't be part of
SQLAlchemy 2.0.   A 2.0-style warning is emitted when autocommit takes
effect, so that the calling code may be adjusted to use an explicit
transaction.

As part of this change, DDL methods such as
:meth:`_schema.MetaData.create_all` when used against a
:class:`_engine.Engine` or :class:`_engine.Connection` will run the
operation in a BEGIN block if one is not started already.

The MySQL and MariaDB dialects now query from the information_schema.tables
system view in order to determine if a particular table exists or not.
Previously, the "DESCRIBE" command was used with an exception catch to
detect non-existent,  which would have the undesirable effect of emitting a
ROLLBACK on the connection. There appeared to be legacy encoding issues
which prevented the use of "SHOW TABLES", for this, but as MySQL support is
now at 5.0.2  or above due to :ticket:`4189`, the information_schema tables
are now available in all cases.

Fixes: #4846
Change-Id: I733a7e0e17477a63607fb9931c87c393bbd7ac57

1 files changed, 38 insertions, 0 deletions

diff --git a/lib/sqlalchemy/testing/schema.py b/lib/sqlalchemy/testing/schema.py
index f5bd1f7a2..8e26d2eaf 100644
--- a/lib/sqlalchemy/testing/schema.py
+++ b/lib/sqlalchemy/testing/schema.py
@@ -9,6 +9,7 @@ from . import config
 from . import exclusions
 from .. import event
 from .. import schema
+from .. import types as sqltypes
 
 
 __all__ = ["Table", "Column"]
@@ -115,6 +116,43 @@ def Column(*args, **kw):
     return col
 
 
+class eq_type_affinity(object):
+    """Helper to compare types inside of datastructures based on affinity.
+
+    E.g.::
+
+        eq_(
+            inspect(connection).get_columns("foo"),
+            [
+                {
+                    "name": "id",
+                    "type": testing.eq_type_affinity(sqltypes.INTEGER),
+                    "nullable": False,
+                    "default": None,
+                    "autoincrement": False,
+                },
+                {
+                    "name": "data",
+                    "type": testing.eq_type_affinity(sqltypes.NullType),
+                    "nullable": True,
+                    "default": None,
+                    "autoincrement": False,
+                },
+            ],
+        )
+
+    """
+
+    def __init__(self, target):
+        self.target = sqltypes.to_instance(target)
+
+    def __eq__(self, other):
+        return self.target._type_affinity is other._type_affinity
+
+    def __ne__(self, other):
+        return self.target._type_affinity is not other._type_affinity
+
+
 def _truncate_name(dialect, name):
     if len(name) > dialect.max_identifier_length:
         return (