1 files changed, 65 insertions, 2 deletions
diff --git a/synapse/storage/databases/main/relations.py b/synapse/storage/databases/main/relations.py
index 907af10995..0a43acda07 100644
--- a/synapse/storage/databases/main/relations.py
+++ b/synapse/storage/databases/main/relations.py
@@ -132,6 +132,69 @@ class RelationsWorkerStore(SQLBaseStore):
             "get_recent_references_for_event", _get_recent_references_for_event_txn
         )
 
+    async def event_includes_relation(self, event_id: str) -> bool:
+        """Check if the given event relates to another event.
+
+        An event has a relation if it has a valid m.relates_to with a rel_type
+        and event_id in the content:
+
+        {
+            "content": {
+                "m.relates_to": {
+                    "rel_type": "m.replace",
+                    "event_id": "$other_event_id"
+                }
+            }
+        }
+
+        Args:
+            event_id: The event to check.
+
+        Returns:
+            True if the event includes a valid relation.
+        """
+
+        result = await self.db_pool.simple_select_one_onecol(
+            table="event_relations",
+            keyvalues={"event_id": event_id},
+            retcol="event_id",
+            allow_none=True,
+            desc="event_includes_relation",
+        )
+        return result is not None
+
+    async def event_is_target_of_relation(self, parent_id: str) -> bool:
+        """Check if the given event is the target of another event's relation.
+
+        An event is the target of an event relation if it has a valid
+        m.relates_to with a rel_type and event_id pointing to parent_id in the
+        content:
+
+        {
+            "content": {
+                "m.relates_to": {
+                    "rel_type": "m.replace",
+                    "event_id": "$parent_id"
+                }
+            }
+        }
+
+        Args:
+            parent_id: The event to check.
+
+        Returns:
+            True if the event is the target of another event's relation.
+        """
+
+        result = await self.db_pool.simple_select_one_onecol(
+            table="event_relations",
+            keyvalues={"relates_to_id": parent_id},
+            retcol="event_id",
+            allow_none=True,
+            desc="event_is_target_of_relation",
+        )
+        return result is not None
+
     @cached(tree=True)
     async def get_aggregation_groups_for_event(
         self,
@@ -362,7 +425,7 @@ class RelationsWorkerStore(SQLBaseStore):
                 %s;
         """
 
-        def _get_if_event_has_relations(txn) -> List[str]:
+        def _get_if_events_have_relations(txn) -> List[str]:
             clauses: List[str] = []
             clause, args = make_in_list_sql_clause(
                 txn.database_engine, "relates_to_id", parent_ids
@@ -387,7 +450,7 @@ class RelationsWorkerStore(SQLBaseStore):
             return [row[0] for row in txn]
 
         return await self.db_pool.runInteraction(
-            "get_if_event_has_relations", _get_if_event_has_relations
+            "get_if_events_have_relations", _get_if_events_have_relations
         )
 
     async def has_user_annotated_event(