mongodb - 他のアイテムがnullでない場合、コレクション内の個別のアイテムを取得します

Question

このようなコレクションを持っています

{
Country : 'XYZ'
Books : [
         {"name" : "book1", "url" : "book1url", "auth_email" : "emailid1"},
         {"name" : "book2", "url" : "book2url", "auth_email" : "emailid2"},
         {"name" : "book3", "url" : "book3url", "auth_email" : "emailid3"},
         {"name" : "book4", "url" : "book4url", "auth_email" : "emailid4"}
         ..........................................
       ]

}

distinct 'Books.name' and corresponding 'Books.email'
場合にのみ抽出したい
'Books.email' is not = ''