- Added new parameter :paramref:`.mapper.confirm_deleted_rows`. Defaults

to True, indicates that a series of DELETE statements should confirm
that the cursor rowcount matches the number of primary keys that should
have matched;  this behavior had been taken off in most cases
(except when version_id is used) to support the unusual edge case of
self-referential ON DELETE CASCADE; to accomodate this, the message
is now just a warning, not an exception, and the flag can be used
to indicate a mapping that expects self-refererntial cascaded
deletes of this nature.  See also :ticket:`2403` for background on the
original change. re: #2403 fix #3007

2 files changed, 40 insertions, 17 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 4747c075d..a939cb9c7 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -110,6 +110,7 @@ class Mapper(_InspectionAttr):
                  include_properties=None,
                  exclude_properties=None,
                  passive_updates=True,
+                 confirm_deleted_rows=True,
                  eager_defaults=False,
                  legacy_is_orphan=False,
                  _compiled_cache_size=100,
@@ -208,6 +209,17 @@ class Mapper(_InspectionAttr):
 
            See the section :ref:`concrete_inheritance` for an example.
 
+        :param confirm_deleted_rows: defaults to True; when a DELETE occurs
+          of one more more rows based on specific primary keys, a warning is
+          emitted when the number of rows matched does not equal the number
+          of rows expected.  This parameter may be set to False to handle the case
+          where database ON DELETE CASCADE rules may be deleting some of those
+          rows automatically.  The warning may be changed to an exception
+          in a future release.
+
+          .. versionadded:: 0.9.4 - added :paramref:`.mapper.confirm_deleted_rows`
+             as well as conditional matched row checking on delete.
+
         :param eager_defaults: if True, the ORM will immediately fetch the
           value of server-generated default values after an INSERT or UPDATE,
           rather than leaving them as expired to be fetched on next access.
@@ -545,9 +557,13 @@ class Mapper(_InspectionAttr):
         self._compiled_cache_size = _compiled_cache_size
         self._reconstructor = None
         self._deprecated_extensions = util.to_list(extension or [])
-
         self.allow_partial_pks = allow_partial_pks
 
+        if self.inherits and not self.concrete:
+            self.confirm_deleted_rows = False
+        else:
+            self.confirm_deleted_rows = confirm_deleted_rows
+
         self._set_with_polymorphic(with_polymorphic)
 
         if isinstance(self.local_table, expression.SelectBase):
diff --git a/lib/sqlalchemy/orm/persistence.py b/lib/sqlalchemy/orm/persistence.py
index d62e803ee..1bd432f15 100644
--- a/lib/sqlalchemy/orm/persistence.py
+++ b/lib/sqlalchemy/orm/persistence.py
@@ -681,19 +681,14 @@ def _emit_delete_statements(base_mapper, uowtransaction, cached_connections,
 
         expected = len(del_objects)
         rows_matched = -1
+        only_warn = False
         if connection.dialect.supports_sane_multi_rowcount:
             c = connection.execute(statement, del_objects)
 
-            # only do a row check if we have versioning turned on.
-            # unfortunately, we *cannot* do a check on the number of
-            # rows matched here in general, as there is the edge case
-            # of a table that has a self-referential foreign key with
-            # ON DELETE CASCADE on it, see #2403.   I'm not sure how we can
-            # resolve this, unless we require special configuration
-            # to enable "count rows" for certain mappings, or to disable
-            # it, or to based on it relationship(), not sure.
-            if need_version_id:
-                rows_matched = c.rowcount
+            if not need_version_id:
+                only_warn = True
+
+            rows_matched = c.rowcount
 
         elif need_version_id:
             if connection.dialect.supports_sane_rowcount:
@@ -713,12 +708,24 @@ def _emit_delete_statements(base_mapper, uowtransaction, cached_connections,
         else:
             connection.execute(statement, del_objects)
 
-        if rows_matched > -1 and expected != rows_matched:
-            raise orm_exc.StaleDataError(
-                "DELETE statement on table '%s' expected to "
-                "delete %d row(s); %d were matched." %
-                (table.description, expected, rows_matched)
-            )
+        if base_mapper.confirm_deleted_rows and \
+            rows_matched > -1 and expected != rows_matched:
+            if only_warn:
+                util.warn(
+                    "DELETE statement on table '%s' expected to "
+                    "delete %d row(s); %d were matched.  Please set "
+                    "confirm_deleted_rows=False within the mapper "
+                    "configuration to prevent this warning." %
+                    (table.description, expected, rows_matched)
+                )
+            else:
+                raise orm_exc.StaleDataError(
+                    "DELETE statement on table '%s' expected to "
+                    "delete %d row(s); %d were matched.  Please set "
+                    "confirm_deleted_rows=False within the mapper "
+                    "configuration to prevent this warning." %
+                    (table.description, expected, rows_matched)
+                )
 
 def _finalize_insert_update_commands(base_mapper, uowtransaction,
                             states_to_insert, states_to_update):