$doc = [ 'tags' => [ [ 'k' => 'name', 'v' => 'A440' ], [ 'k' => 'highway', 'v' => 'secondary' ], [ 'k' => 'oneway', 'v' => 'yes' ] ] ]; $db->poi->createIndex( [ 'tags.v' => 1, 'tags.k' => 1 ] ); // Road with name=Strand $db->poi->find( [ 'tags' => [ '$elemMatch' => [ 'k' : 'name', 'v' : 'Strand' ] ] ] ); // All roads $db->poi->find( [ 'tags.k' => 'highway' ] ); Two indexes required: one for key/value combinations one for "all roads" question (on %tags.k%) Good for finding key/value combinations