Fix pickle and deepcopy of graph types (#1133)

Since the types of `Relationship`s are tied to the `Graph` object they belong
to, fixing `pickle` support for graph types means that `Relationship`s with
the same name will have a different type after `deepcopy`ing or pickling and
unpickling them or their graph.

Author: robsdedude

CHANGELOG.md

@@ -3,7 +3,8 @@
 See also https://github.com/neo4j/neo4j-python-driver/wiki for a full changelog.
 
 ## NEXT RELEASE
-- No breaking or major changes.
+- Since the types of `Relationship`s are tied to the `Graph` object they belong to, fixing `pickle` support for graph types means that `Relationship`s with the same name will have a different type after `deepcopy`ing or pickling and unpickling them or their graph.
+  For more details, see https://github.com/neo4j/neo4j-python-driver/pull/1133
 
 
 ## Version 5.27

src/neo4j/graph/__init__.py

@@ -80,6 +80,21 @@ def relationship_type(self, name: str) -> type[Relationship]:
             )
         return cls
 
+    def __reduce__(self):
+        state = self.__dict__.copy()
+        relationship_types = tuple(state.pop("_relationship_types", {}).keys())
+        restore_args = (relationship_types,)
+        return Graph._restore, restore_args, state
+
+    @staticmethod
+    def _restore(relationship_types: tuple[str, ...]) -> Graph:
+        graph = Graph().__new__(Graph)
+        graph.__dict__["_relationship_types"] = {
+            name: type(str(name), (Relationship,), {})
+            for name in relationship_types
+        }
+        return graph
+
 
 class Entity(t.Mapping[str, t.Any]):
     """
@@ -287,6 +302,14 @@ def type(self) -> str:
         """
         return type(self).__name__
 
+    def __reduce__(self):
+        return Relationship._restore, (self.graph, self.type), self.__dict__
+
+    @staticmethod
+    def _restore(graph: Graph, name: str) -> Relationship:
+        type_ = graph.relationship_type(name)
+        return type_.__new__(type_)
+
 
 class Path:
     """Self-contained graph path."""

tests/unit/common/graph/__init__.py

@@ -0,0 +1,14 @@
+# Copyright (c) "Neo4j"
+# Neo4j Sweden AB [https://neo4j.com]
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.