Added support for calling the outconverter when null values are fetched

from the database (#107).

Author: anthony-tuininga

doc/src/api_manual/cursor.rst

@@ -371,7 +371,7 @@ Cursor Methods
 
 
 .. method:: Cursor.var(typ, [size, arraysize, inconverter, outconverter, \
-        typename, encoding_errors, bypass_decode])
+        typename, encoding_errors, bypass_decode, convert_nulls])
 
     Creates a variable with the specified characteristics. This method was
     designed for use with PL/SQL in/out variables where the length or type
@@ -442,10 +442,20 @@ Cursor Methods
     meaning that python-oracledb does not do any decoding. See :ref:`Fetching raw
     data <fetching-raw-data>` for more information.
 
+    The ``convert_nulls`` parameter, if specified, should be passed a boolean
+    value. Passing the value ``True`` causes the ``outconverter`` to be called
+    when a null value is fetched from the database; otherwise, the
+    ``outconverter`` is only called when non-null values are fetched from the
+    database.
+
     For consistency and compliance with the PEP 8 naming style, the
     parameter `encodingErrors` was renamed to `encoding_errors`. The old
     name will continue to work as a keyword parameter for a period of time.
 
+    .. versionchanged:: 1.4
+
+        The ``convert_nulls`` parameter was added.
+
     .. note::
 
         The DB API definition does not define this method.

doc/src/api_manual/variable.rst

@@ -50,6 +50,13 @@ Variable Attributes
     name will continue to work for a period of time.
 
 
+.. attribute:: Variable.convert_nulls
+
+   This read-only attribute returns whether the :data:`~Variable.outconverter`
+   method is called when null values are fetched from the database.
+
+   .. versionadded:: 1.4
+
 .. attribute:: Variable.inconverter
 
     This read-write attribute specifies the method used to convert data from

doc/src/release_notes.rst

@@ -74,6 +74,11 @@ Thick Mode Changes
 Common Changes
 ++++++++++++++
 
+#)  Added support for the :attr:`~Variable.outconverter` being called when a
+    null value is fetched from the database and the new parameter
+    ``convert_nulls`` to the method :meth:`Cursor.var()` is passed the value
+    ``True``
+    (`issue 107 <https://github.com/oracle/python-oracledb/issues/107>`__).
 #)  Replaced fixed 7-tuple for the cursor metadata found in
     :data:`Cursor.description` with a class which provides additional
     information such as the database object type and whether the column

src/oracledb/base_impl.pxd

@@ -333,6 +333,7 @@ cdef class BaseVarImpl:
         readonly bint bypass_decode
         readonly bint is_array
         readonly bint nulls_allowed
+        readonly bint convert_nulls
         public uint32_t num_elements_in_array
         readonly DbType dbtype
         readonly BaseDbObjectTypeImpl objtype

src/oracledb/cursor.py

@@ -743,6 +743,7 @@ def var(self,
             typename: str=None,
             encoding_errors: str=None,
             bypass_decode: bool=False,
+            convert_nulls: bool=False,
             *,
             encodingErrors: str=None) -> "Var":
         """
@@ -794,6 +795,9 @@ def var(self,
         DB_TYPE_VARCHAR, DB_TYPE_CHAR, DB_TYPE_NVARCHAR, DB_TYPE_NCHAR and
         DB_TYPE_LONG to be returned as bytes instead of str, meaning that
         oracledb doesn't do any decoding.
+
+        The convert_nulls parameter specifies whether the outconverter should
+        be called when null values are fetched from the database.
         """
         self._verify_open()
         if typename is not None:
@@ -808,4 +812,5 @@ def var(self,
             encoding_errors = encodingErrors
         return self._impl.create_var(self.connection, typ, size, arraysize,
                                      inconverter, outconverter,
-                                     encoding_errors, bypass_decode)
+                                     encoding_errors, bypass_decode,
+                                     convert_nulls=convert_nulls)

src/oracledb/impl/base/cursor.pyx

@@ -403,7 +403,8 @@ cdef class BaseCursorImpl:
     def create_var(self, object conn, object typ, uint32_t size=0,
                    uint32_t num_elements=1, object inconverter=None,
                    object outconverter=None, str encoding_errors=None,
-                   bint bypass_decode=False, bint is_array=False):
+                   bint bypass_decode=False, bint is_array=False,
+                   bint convert_nulls=False):
         cdef BaseVarImpl var_impl
         var_impl = self._create_var_impl(conn)
         var_impl._set_type_info_from_type(typ)
@@ -413,6 +414,7 @@ cdef class BaseCursorImpl:
         var_impl.outconverter = outconverter
         var_impl.bypass_decode = bypass_decode
         var_impl.is_array = is_array
+        var_impl.convert_nulls = convert_nulls
         var_impl._finalize_init()
         return PY_TYPE_VAR._from_impl(var_impl)
 

src/oracledb/impl/thick/var.pyx

@@ -1,5 +1,5 @@
 #------------------------------------------------------------------------------
-# Copyright (c) 2020, 2022, Oracle and/or its affiliates.
+# Copyright (c) 2020, 2023, Oracle and/or its affiliates.
 #
 # This software is dual-licensed to you under the Universal Permissive License
 # (UPL) 1.0 as shown at https://oss.oracle.com/licenses/upl and Apache License
@@ -276,3 +276,5 @@ cdef class ThickVarImpl(BaseVarImpl):
             if self.outconverter is not None:
                 value = self.outconverter(value)
             return value
+        elif self.convert_nulls:
+            return self.outconverter(None)

src/oracledb/impl/thin/messages.pyx

@@ -494,7 +494,7 @@ cdef class MessageWithData(Message):
                 num_elements = self.row_index
             for i in range(num_elements):
                 value = var_impl._values[i]
-                if value is None:
+                if value is None and not var_impl.convert_nulls:
                     continue
                 if isinstance(value, list):
                     for j, element_value in enumerate(value):

src/oracledb/var.py

@@ -90,6 +90,14 @@ def bufferSize(self) -> int:
         """
         return self.buffer_size
 
+    @property
+    def convert_nulls(self) -> bool:
+        """
+        This read-only attribute returns whether null values are converted
+        using the supplied ``outconverter``.
+        """
+        return self._impl.convert_nulls
+
     def getvalue(self, pos: int=0) -> Any:
         """
         Return the value at the given position in the variable. For variables

tests/test_3700_var.py

@@ -433,5 +433,26 @@ def test_3729_deprecations(self):
         self.assertEqual(var.actualElements, 200)
         self.assertEqual(var.numElements, 200)
 
+    def test_3730_convert_nulls(self):
+        "3730 - test calling of outconverter with null values"
+        def type_handler(cursor, metadata):
+            return cursor.var(metadata.type_code,
+                              outconverter=lambda v: f"|{v}|" if v else '',
+                              convert_nulls=True, arraysize=cursor.arraysize)
+        self.cursor.outputtypehandler = type_handler
+        self.cursor.execute("""
+                select 'First - A', 'First - B' from dual
+                union all
+                select 'Second - A', null from dual
+                union all
+                select null, 'Third - B' from dual""")
+        rows = self.cursor.fetchall()
+        expected_rows = [
+            ('|First - A|', '|First - B|'),
+            ('|Second - A|', ''),
+            ('', '|Third - B|')
+        ]
+        self.assertEqual(rows, expected_rows)
+
 if __name__ == "__main__":
     test_env.run_test_cases()