Workaround non-compatible type.adapt() for SQLAlchemy < 1.1

The ndb change that makes use of String.adapt() to produce a new
object breaks on SQLAlchemy < 1.1 because adapt() there does
not allow for kwargs to override those already
present in the type.

Change-Id: I8cc79dc9bebcb3cb3accf76559bc969c2dae7ed9

oslo_db/sqlalchemy/compat/utils.py

@@ -43,3 +43,27 @@ def get_postgresql_enums(conn):
         return [e['name'] for e in sqlalchemy.inspect(conn).get_enums()]
     else:
         return conn.dialect._load_enums(conn).keys()
+
+
+def adapt_type_object(type_object, target_class, *args, **kw):
+    """Call the adapt() method on a type.
+
+    For SQLAlchemy 1.0, runs a local version of constructor_copy() that
+    allows keyword arguments to be overridden.
+
+    See https://github.com/zzzeek/sqlalchemy/commit/\
+    ceeb033054f09db3eccbde3fad1941ec42919a54
+
+    """
+    if sqla_110:
+        return type_object.adapt(target_class, *args, **kw)
+    else:
+        # NOTE(zzzeek): this only works for basic types, won't work for
+        # schema types like Enum, Boolean
+        # NOTE(zzzeek): this code can be removed once requirements
+        # are at SQLAlchemy >= 1.1
+        names = sqlalchemy.util.get_cls_kwargs(target_class)
+        kw.update(
+            (k, type_object.__dict__[k]) for k in names.difference(kw)
+            if k in type_object.__dict__)
+        return target_class(*args, **kw)

oslo_db/sqlalchemy/ndb.py

@@ -17,6 +17,7 @@ import re
 
 import debtcollector.removals
 
+from oslo_db.sqlalchemy.compat import utils as compat_utils
 from oslo_db.sqlalchemy.types import String
 
 from sqlalchemy import event, schema
@@ -103,8 +104,8 @@ def _compile_ndb_string(element, compiler, **kw):
         return compiler.visit_string(element, **kw)
 
     if element.mysql_ndb_length:
-        effective_type = element.adapt(
-            _String, length=element.mysql_ndb_length)
+        effective_type = compat_utils.adapt_type_object(
+            element, _String, length=element.mysql_ndb_length)
         return compiler.visit_string(effective_type, **kw)
     elif element.mysql_ndb_type:
         effective_type = to_instance(element.mysql_ndb_type)