fix: raise an error instead of a warning using nextset in pipeline mode

Note: the tests, intentionally, don't pass, because they expects
execute() results to clobber the previous ones rather than accumulating.
This behaviour is to be changed in a further commit.

See #604.

diff --git a/docs/news.rst b/docs/news.rst
index 5a7a2afe858d7f05d2243164f727ae9be5734bec..e3e4b09e306a13f40e53f7d11cdb7cdf994adc76 100644 (file)
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -15,6 +15,9 @@ Psycopg 3.2 (unreleased)
 
 - Add support for libpq functions to close prepared statements and portals
   introduced in libpq v17 (:ticket:`#603`).
+- Disable receiving more than one result on the same cursor in pipeline mode,
+  to iterate through `~Cursor.nextset()`. The behaviour was different than
+  in non-pipeline mode and not totally reliable (:ticket:`#604`).
 
 
 Psycopg 3.1.10 (unreleased)

diff --git a/psycopg/psycopg/cursor.py b/psycopg/psycopg/cursor.py
index 3b7182a258139f12473cfde7a5aa590709d56105..356e94018eb3aad99a70835944a984a0fb4706a2 100644 (file)
--- a/psycopg/psycopg/cursor.py
+++ b/psycopg/psycopg/cursor.py
@@ -9,7 +9,6 @@ from types import TracebackType
 from typing import Any, Generic, Iterable, Iterator, List
 from typing import Optional, NoReturn, Sequence, Tuple, Type, TypeVar
 from typing import overload, TYPE_CHECKING
-from warnings import warn
 from contextlib import contextmanager
 
 from . import pq
@@ -157,16 +156,17 @@ class BaseCursor(Generic[ConnectionType, Row]):
         Return `!True` if a new result is available, which will be the one
         methods `!fetch*()` will operate on.
         """
-        # Raise a warning if people is calling nextset() in pipeline mode
-        # after a sequence of execute() in pipeline mode. Pipeline accumulating
-        # execute() results in the cursor is an unintended difference w.r.t.
-        # non-pipeline mode.
+        # Python 3.1 would accumulate execute() results in the cursor, but it
+        # was an undesired difference with non-pipeline mode, so it was
+        # deprecated in 3.1.10; in 3.2 we moved to clobber previous execute()
+        # results and, because running multiple statements in the same
+        # execute() is not supported in pipeline mode, there is no reason to
+        # support nextset(). This error replaces the previous warning.
         if self._execmany_returning is None and self._conn._pipeline:
-            warn(
+            raise e.NotSupportedError(
                 "using nextset() in pipeline mode for several execute() is"
-                " deprecated and will be dropped in 3.2; please use different"
-                " cursors to receive more than one result",
-                DeprecationWarning,
+                " not supported. Please use several cursors to receive more"
+                " than one result"
             )
 
         if self._iresult < len(self._results) - 1:

diff --git a/tests/test_pipeline.py b/tests/test_pipeline.py
index 12180bdebaa07f159491b017cb54478b4ef44bf7..77c3c6f7ce3c957cdcadeb5fe82ea845f13dacbc 100644 (file)
--- a/tests/test_pipeline.py
+++ b/tests/test_pipeline.py
@@ -595,7 +595,7 @@ def test_concurrency(conn):
     assert after > before
 
 
-def test_execute_nextset_warning(conn):
+def test_execute_nextset_error(conn):
     cur = conn.cursor()
     cur.execute("select 1")
     cur.execute("select 2")
@@ -608,8 +608,6 @@ def test_execute_nextset_warning(conn):
         cur.execute("select 1")
         cur.execute("select 2")
 
-        # WARNING: this behavior is unintentional and will be changed in 3.2
-        assert cur.fetchall() == [(1,)]
-        with pytest.warns(DeprecationWarning, match="nextset"):
-            assert cur.nextset()
         assert cur.fetchall() == [(2,)]
+        with pytest.raises(psycopg.NotSupportedError, match="nextset"):
+            assert cur.nextset()

diff --git a/tests/test_pipeline_async.py b/tests/test_pipeline_async.py
index 484cce4dcab0c69df69d902582f55c35d5c2955f..c578618fd7b188f3de3e6b9962a47a5105686785 100644 (file)
--- a/tests/test_pipeline_async.py
+++ b/tests/test_pipeline_async.py
@@ -603,7 +603,7 @@ async def test_concurrency(aconn):
     assert after > before
 
 
-async def test_execute_nextset_warning(aconn):
+async def test_execute_nextset_error(aconn):
     cur = aconn.cursor()
     await cur.execute("select 1")
     await cur.execute("select 2")
@@ -616,8 +616,6 @@ async def test_execute_nextset_warning(aconn):
         await cur.execute("select 1")
         await cur.execute("select 2")
 
-        # WARNING: this behavior is unintentional and will be changed in 3.2
-        assert (await cur.fetchall()) == [(1,)]
-        with pytest.warns(DeprecationWarning, match="nextset"):
-            assert cur.nextset()
         assert (await cur.fetchall()) == [(2,)]
+        with pytest.raises(psycopg.NotSupportedError, match="nextset"):
+            assert cur.nextset()