MongoDB: cross-collection queries

[Phani]

Assuming a setup like this:\[code\]blogposts{ title:"Example", slug:"example-post" tags: ["foo", "bar"]},{ title:"Example2", slug:"example2" tags: ["foo"]}news{ headline: "Test" slug: "test-news" tags: ["bar"]}\[/code\]I know I can get all the blog posts with a specific tag:\[code\]$cursor = $blogposts->find(array('tags' => 'bar'));\[/code\]but is there any way to query multiple collections at once in order to get all documents with the tag? E.g. to show all content with the tag 'bar'.