mongodb - Best way to return documents that include a count of an internal collection? -

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I have a collection with documents, such as the following: 

  {title: First, "Everything": ['Something', 'Something']}   
 And I would like to get output like the following:  
  {"First", 3}, {"seconds, 2}   
 What's the best way to do this? I call it the  map  function Implemented by:  
  db.coll.find (). Map (function) {return {title: Item.title, count: item.sub_items.length};}) ;   
 When trying to get the above results, would I be better to use and use something to be better than a display perspective if you have  MongoDB 2.6 or later < / Strong>, you can or   
 
 $ size  from the document:  
 
 count The power and the total number of items in the array.   
 Below is an unwanted example:  
  db.coll.aggregate ({{"$ project": {"Title": 1, "count": {"$ size": "$ sub_items"}}}))

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