1. A method comprising, by one or more computing devices: receiving, from a client system of a first user, a search query requesting objects of a first object type, the search query comprising an inner query requesting objects of a second object type; identifying one or more objects of the second object type requested by the inner query using an inverted index of a second data store corresponding to the second object type; identifying, for each of the identified one or more objects of the second object type, one or more objects of the first object type requested by the search query, the one or more objects of the first object type being identified using an inverted index of a first data store corresponding to the first object type; aggregating a plurality of search results responsive to the search query, each search result corresponding to an identified object of the first object type; and sending, to the client system of the first user, one or more of the aggregated search results.