MongoDB check exists in array

collection 'books':

array (
  '_id' => new MongoId("4e242b0ea5bb1bb00b000000"),
  'book' => 
  array (
    '0' => 1,
    '1' => 2,
    '开发者_C百科2' => 3,
    '3' => 14,
    '4' => 15,
  ),
  'book_count' => 5,
  'user_name' => 'john',
)

How can I check where 'some book' in an array 'book'?

is this only way to check ?

db.books.count({user_name:'john', book:1})

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Yes, although the following would be faster

db.books.find({user_name:'john', book:1}).limit(1) != null