title: How could I remove some items in 2 level deep nested array
body: <p>I want to remote  items only contain white spaces <code>"     "</code></p>
  
  <p>But my query doesn't work, any suggestion</p>
  
  <h1>query</h1>
  
  <pre><code>  db[source_collection].update({
      '_id': customer._id
    }, {
      '$pull': {
        "records.0.items": {
          $regex: /^\s*$/
        }
      }
    });
  </code></pre>
  
  <h1>Document</h1>
  
  <pre><code>    {
          "_id" : "025daee4b9b9ba36ed244bb594313ff9",
          "records" : [
              {
                  "items" : [
                      "7089 "
                  ]
              },
              {
  
                  "items" : [
                      "     ",
                      "78059"
                  ]
              },
              {
  
                  "items" : [
                      "     ",
                      "5645 "
                  ]
              }
          ]
      }
  </code></pre>