Let's say I indexed 5 documents each from different authors. The node's metadata has the author on it. The docs seem to indicate I can only add a metadata filter to the retriever then instantiate the query_engine. That means I'm constantly having to re-create the engine if the metadata over which I'm querying changes, like searching for author1 in query1 then author2 in query2.
Other frameworks allow me to filter at query time.
