- [feature] Added a new oracle create_engine() flag

coerce_to_decimal=False, disables the precision
numeric handling which can add lots of overhead
by converting all numeric values to
Decimal.  [ticket:2399]

diff --git a/CHANGES b/CHANGES
index c954c2de62d4c6a242095244ec1681fddf5c1e27..0c4267fb0a7690a472e471141d0d3f5063635ea6 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -92,6 +92,11 @@ CHANGES
     to mu_mind for the patch here. [ticket:2394]
 
 - oracle
+  - [feature] Added a new create_engine() flag
+    coerce_to_decimal=False, disables the precision
+    numeric handling which can add lots of overhead
+    by converting all numeric values to 
+    Decimal.  [ticket:2399]
 
   - [bug] Added missing compilation support for 
     LONG [ticket:2401]

diff --git a/lib/sqlalchemy/dialects/oracle/cx_oracle.py b/lib/sqlalchemy/dialects/oracle/cx_oracle.py
index 64526d213eb98ea29818aca2f0090dec12e2080b..5001acca34886e15a19f131c953bdb70532d5dd4 100644 (file)
--- a/lib/sqlalchemy/dialects/oracle/cx_oracle.py
+++ b/lib/sqlalchemy/dialects/oracle/cx_oracle.py
@@ -77,7 +77,7 @@ with this feature but it should be regarded as experimental.
 Precision Numerics
 ------------------
 
-The SQLAlchemy dialect goes thorugh a lot of steps to ensure
+The SQLAlchemy dialect goes through a lot of steps to ensure
 that decimal numbers are sent and received with full accuracy.
 An "outputtypehandler" callable is associated with each
 cx_oracle connection object which detects numeric types and
@@ -89,6 +89,21 @@ this behavior, and will coerce the ``Decimal`` to ``float`` if
 the ``asdecimal`` flag is ``False`` (default on :class:`.Float`,
 optional on :class:`.Numeric`).
 
+Because the handler coerces to ``Decimal`` in all cases first,
+the feature can detract significantly from performance.
+If precision numerics aren't required, the decimal handling
+can be disabled by passing the flag ``coerce_to_decimal=False``
+to :func:`.create_engine`::
+
+    engine = create_engine("oracle+cx_oracle://dsn", 
+                        coerce_to_decimal=False)
+
+The ``coerce_to_decimal`` flag is new in 0.7.6.
+
+Another alternative to performance is to use the 
+`cdecimal <http://pypi.python.org/pypi/cdecimal/>`_ library; 
+see :class:`.Numeric` for additional notes.
+
 The handler attempts to use the "precision" and "scale"
 attributes of the result set column to best determine if
 subsequent incoming values should be received as ``Decimal`` as
@@ -468,6 +483,7 @@ class OracleDialect_cx_oracle(OracleDialect):
                 auto_convert_lobs=True, 
                 threaded=True, 
                 allow_twophase=True, 
+                coerce_to_decimal=True,
                 arraysize=50, **kwargs):
         OracleDialect.__init__(self, **kwargs)
         self.threaded = threaded
@@ -491,7 +507,12 @@ class OracleDialect_cx_oracle(OracleDialect):
         self._cx_oracle_unicode_types = types("UNICODE", "NCLOB")
         self._cx_oracle_binary_types = types("BFILE", "CLOB", "NCLOB", "BLOB") 
         self.supports_unicode_binds = self.cx_oracle_ver >= (5, 0)
-        self.supports_native_decimal = self.cx_oracle_ver >= (5, 0)
+
+        self.supports_native_decimal = (
+                                        self.cx_oracle_ver >= (5, 0) and 
+                                        coerce_to_decimal
+                                    )
+
         self._cx_oracle_native_nvarchar = self.cx_oracle_ver >= (5, 0)
 
         if self.cx_oracle_ver is None:
@@ -603,7 +624,9 @@ class OracleDialect_cx_oracle(OracleDialect):
                                     size, precision, scale):
             # convert all NUMBER with precision + positive scale to Decimal
             # this almost allows "native decimal" mode.
-            if defaultType == cx_Oracle.NUMBER and precision and scale > 0:
+            if self.supports_native_decimal and \
+                    defaultType == cx_Oracle.NUMBER and \
+                    precision and scale > 0:
                 return cursor.var(
                             cx_Oracle.STRING, 
                             255, 
@@ -614,7 +637,8 @@ class OracleDialect_cx_oracle(OracleDialect):
             # make a decision based on each value received - the type 
             # may change from row to row (!).   This kills
             # off "native decimal" mode, handlers still needed.
-            elif defaultType == cx_Oracle.NUMBER \
+            elif self.supports_native_decimal and \
+                    defaultType == cx_Oracle.NUMBER \
                     and not precision and scale <= 0:
                 return cursor.var(
                             cx_Oracle.STRING, 

diff --git a/test/dialect/test_oracle.py b/test/dialect/test_oracle.py
index ad9220076e3a123693c291fc72685f8f9b64def9..6830295498e383531c50459cf0b36c8554990259 100644 (file)
--- a/test/dialect/test_oracle.py
+++ b/test/dialect/test_oracle.py
@@ -880,6 +880,15 @@ class TypesTest(fixtures.TestBase):
         finally:
             t1.drop()
 
+
+    def test_numeric_no_decimal_mode(self):
+        engine = testing_engine(options=dict(coerce_to_decimal=False))
+        value = engine.scalar("SELECT 5.66 FROM DUAL")
+        assert isinstance(value, float)
+
+        value = testing.db.scalar("SELECT 5.66 FROM DUAL")
+        assert isinstance(value, decimal.Decimal)
+
     @testing.provide_metadata
     def test_numerics_broken_inspection(self):
         """Numeric scenarios where Oracle type info is 'broken',