title: Nested aggregation in nested field?
body: <p>I am new to elasticsearch and don't know a lot about aggregations but I have this ES6 mapping:</p>
  
  <pre><code>{
      "mappings": {
          "test": {
              "properties": {
                  "id": {
                      "type": "integer"
                  }
                  "countries": {
                      "type": "nested",
                      "properties": {
                          "global_id": {
                              "type": "keyword"
                          },
                          "name": {
                              "type": "text",
                              "fields": {
                                  "raw": {
                                      "type": "keyword"
                                  }
                              }
                          }
                      }
                  },
                  "areas": {
                      "type": "nested",
                      "properties": {
                          "global_id": {
                              "type": "keyword"
                          },
                          "name": {
                              "type": "text",
                              "fields": {
                                  "raw": {
                                      "type": "keyword"
                                  }
                              }
                          },
                          "parent_global_id": {
                              "type": "keyword"
                          }
                      }
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>How can I get all documents grouped by <code>areas</code> which is then grouped by <code>countries</code>. Also the document has to be returned in full, not just the nested document. Is this even possible ?</p>