title: MongoDB: how to add the specific fields from one query with alias to result of another query using Java (with or without Spring)?
body: <p>If we have collection "orders"</p>
  
  <pre><code>{"_id":"1",
   "currency": "USD"//...
  }
  </code></pre>
  
  <p>And collection "order_items"</p>
  
  <pre><code>{"_id":"1",
   "order":"1",
   "product":"p1",
   "totalItemAmount": 25
  },
   {"_id":"2",
   "order":"1",
   "product":"p2",
   "totalItemAmount": 50
  }
  </code></pre>
  
  <p>How to get such result </p>
  
  <pre><code>[{
  "orderId": "1",
  "currency": "USD",
  "products": ["p1", "p2"]
  "totalOrderAmount": "75"
  }]
  </code></pre>
  
  <p>using Java (with or without Spring)?</p>