Implement _simple_delete_many_txn, use it to delete devices

(But this doesn't implement the same for deleting access tokens or e2e keys.

Also respond to code review.

synapse/storage/_base.py

@@ -840,6 +840,47 @@ class SQLBaseStore(object):
 
         return txn.execute(sql, keyvalues.values())
 
+    def _simple_delete_many(self, table, column, iterable, keyvalues, desc):
+        return self.runInteraction(
+            desc, self._simple_delete_many_txn, table, column, iterable, keyvalues
+        )
+
+    @staticmethod
+    def _simple_delete_many_txn(txn, table, column, iterable, keyvalues):
+        """Executes a DELETE query on the named table.
+
+        Filters rows by if value of `column` is in `iterable`.
+
+        Args:
+            txn : Transaction object
+            table : string giving the table name
+            column : column name to test for inclusion against `iterable`
+            iterable : list
+            keyvalues : dict of column names and values to select the rows with
+        """
+        if not iterable:
+            return
+
+        sql = "DELETE FROM %s" % table
+
+        clauses = []
+        values = []
+        clauses.append(
+            "%s IN (%s)" % (column, ",".join("?" for _ in iterable))
+        )
+        values.extend(iterable)
+
+        for key, value in keyvalues.items():
+            clauses.append("%s = ?" % (key,))
+            values.append(value)
+
+        if clauses:
+            sql = "%s WHERE %s" % (
+                sql,
+                " AND ".join(clauses),
+            )
+        return txn.execute(sql, values)
+
     def _get_cache_dict(self, db_conn, table, entity_column, stream_column,
                         max_value, limit=100000):
         # Fetch a mapping of room_id -> max stream position for "recent" rooms.

synapse/storage/devices.py

@@ -108,6 +108,23 @@ class DeviceStore(SQLBaseStore):
             desc="delete_device",
         )
 
+    def delete_devices(self, user_id, device_ids):
+        """Deletes several devices.
+
+        Args:
+            user_id (str): The ID of the user which owns the devices
+            device_ids (list): The IDs of the devices to delete
+        Returns:
+            defer.Deferred
+        """
+        return self._simple_delete_many(
+            table="devices",
+            column="device_id",
+            iterable=device_ids,
+            keyvalues={"user_id": user_id},
+            desc="delete_devices",
+        )
+
     def update_device(self, user_id, device_id, new_display_name=None):
         """Update a device.