[{"name":"doc 1","tables":[{"name":"table 1a","lines":[{"key_values":[{"key":"apples","value":"1"},{"key":"bananas","value":"2"},{"key":"pears","value":"3"}]},{"key_values":[{"key":"apples","value":"4"},{"key":"bananas","value":"5"},{"key":"pears","value":"6"}]},{"key_values":[{"key":"apples","value":"7"},{"key":"bananas","value":"8"},{"key":"pears","value":"9"}]}]},{"name":"table 1b","lines":[{"key_values":[{"key":"apples","value":"1"},{"key":"bananas","value":"5"},{"key":"pears","value":"3"}]},{"key_values":[{"key":"apples","value":"2"},{"key":"bananas","value":"4"},{"key":"pears","value":"6"}]},{"key_values":[{"key":"apples","value":"1"},{"key":"bananas","value":"9"},{"key":"pears","value":"6"}]}]}]},{"name":"doc 2","tables":[{"name":"table 2a","lines":[{"key_values":[{"key":"apples","value":"5"},{"key":"bananas","value":"2"},{"key":"pears","value":"7"}]},{"key_values":[{"key":"apples","value":"4"},{"key":"bananas","value":"4"},{"key":"pears","value":"1"}]},{"key_values":[{"key":"apples","value":"3"},{"key":"bananas","value":"9"},{"key":"pears","value":"8"}]}]},{"name":"table 2b","lines":[{"key_values":[{"key":"apples","value":"1"},{"key":"bananas","value":"6"},{"key":"pears","value":"5"}]},{"key_values":[{"key":"apples","value":"7"},{"key":"bananas","value":"2"},{"key":"pears","value":"4"}]},{"key_values":[{"key":"apples","value":"8"},{"key":"bananas","value":"9"},{"key":"pears","value":"3"}]}]}]}]

db.collection.aggregate([{"$match":{"tables.lines":{"$elemMatch":{"key_values":{"$elemMatch":{"key":"apples","value":"5"}}}}}}])