- reorganize schema_translate_map to be succinct and gain the performance

back by using an attrgetter for the default case

1 files changed, 52 insertions, 4 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index b244d746c..628d06183 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -30,20 +30,19 @@ as components in SQL expressions.
 """
 from __future__ import absolute_import
 
-import inspect
 from .. import exc, util, event, inspection
 from .base import SchemaEventTarget, DialectKWArgs
+import operator
 from . import visitors
 from . import type_api
 from .base import _bind_or_error, ColumnCollection
-from .elements import ClauseElement, ColumnClause, _truncated_label, \
+from .elements import ClauseElement, ColumnClause, \
     _as_truncated, TextClause, _literal_as_text,\
-    ColumnElement, _find_columns, quoted_name
+    ColumnElement, quoted_name
 from .selectable import TableClause
 import collections
 import sqlalchemy
 from . import ddl
-import types
 
 RETAIN_SCHEMA = util.symbol('retain_schema')
 
@@ -3862,3 +3861,52 @@ class ThreadLocalMetaData(MetaData):
         for e in self.__engines.values():
             if hasattr(e, 'dispose'):
                 e.dispose()
+
+
+class _SchemaTranslateMap(object):
+    """Provide translation of schema names based on a mapping.
+
+    Also provides helpers for producing cache keys and optimized
+    access when no mapping is present.
+
+    Used by the :paramref:`.Connection.execution_options.schema_translate_map`
+    feature.
+
+    .. versionadded:: 1.1
+
+
+    """
+    __slots__ = 'map_', '__call__', 'hash_key', 'is_default'
+
+    _default_schema_getter = operator.attrgetter("schema")
+
+    def __init__(self, map_):
+        self.map_ = map_
+        if map_ is not None:
+            def schema_for_object(obj):
+                effective_schema = self._default_schema_getter(obj)
+                effective_schema = map_.get(effective_schema, effective_schema)
+                return effective_schema
+            self.__call__ = schema_for_object
+            self.hash_key = ";".join(
+                "%s=%s" % (k, map_[k])
+                for k in sorted(map_)
+            )
+            self.is_default = False
+        else:
+            self.hash_key = 0
+            self.__call__ = self._default_schema_getter
+            self.is_default = True
+
+    @classmethod
+    def _schema_getter(cls, map_):
+        if map_ is None:
+            return _default_schema_map
+        elif isinstance(map_, _SchemaTranslateMap):
+            return map_
+        else:
+            return _SchemaTranslateMap(map_)
+
+_default_schema_map = _SchemaTranslateMap(None)
+_schema_getter = _SchemaTranslateMap._schema_getter
+