Sorting by _score on an aggregation

Hello, I have the following schema for an index, with some example documents. My use-case is that I'm indexing a book and I am indexing by page. I'm trying to make a query against the contents of each page and return the most relevant page from top N most relevant books, but I'm having trouble returning them by their _score field in the proper order:

PUT my-index
{}

PUT my-index/_mapping
{
    "properties": {
        "page": {
            "type": "long"
        },
        "title": {
            "type": "keyword"
        },
        "content": {
            "type": "text"
        }
    }
}

POST _bulk
{ "index" : { "_index" : "my-index", "_id" : "doc_1.pg_1" } }
{ "page" : 1, "title": "doc_1", "content": "a quick brown fox jumped over the lazy dog ..."}
{ "index" : { "_index" : "my-index", "_id" : "doc_1.pg_2" } }
{ "page" : 2, "title": "doc_1", "content": "... and the fox landed in a briar patch"}
{ "index" : { "_index" : "my-index", "_id" : "doc_2.pg_1" } }
{ "page" : 1, "title": "doc_2", "content": "a slow orange fox leapt over the barky dog ..."}
{ "index" : { "_index" : "my-index", "_id" : "doc_2.pg_2" } }
{ "page" : 2, "title": "doc_2", "content": "... and the dog lept and got the fox"}

So far I've created the following query aggregation to get the most relevant page of the each doc in the corpus:

GET my-index/_search
{
  "size":0,
  "query" : {
    "simple_query_string": {
      "query": "the",
      "fields": ["content"]
    }     
  },
  "aggs": {
    "by_title" : {
      "terms" : {
        "field" : "title"
      },
      "aggs": {
        "get_top_scoring_page": {
          "top_hits": {
           "sort": {"_score": {"order": "desc"}},
            "size": 1,
            "highlight": {"fields": {"content": {}}}
          }
        }
      }
    }
  }
}

And here's what it returns:

{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 4,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "by_title" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "doc_1",
          "doc_count" : 2,
          "get_top_scoring_page" : {
            "hits" : {
              "total" : {
                "value" : 2,
                "relation" : "eq"
              },
              "max_score" : 0.10795845,
              "hits" : [
                {
                  "_index" : "my-index",
                  "_type" : "_doc",
                  "_id" : "doc_1.pg_2",
                  "_score" : 0.10795845,
                  "_source" : {
                    "page" : 2,
                    "title" : "doc_1",
                    "content" : "... and the fox landed in a briar patch"
                  },
                  "highlight" : {
                    "content" : [
                      "... and <em>the</em> fox landed in a briar patch"
                    ]
                  }
                }
              ]
            }
          }
        },
        {
          "key" : "doc_2",
          "doc_count" : 2,
          "get_top_scoring_page" : {
            "hits" : {
              "total" : {
                "value" : 2,
                "relation" : "eq"
              },
              "max_score" : 0.14730778,
              "hits" : [
                {
                  "_index" : "my-index",
                  "_type" : "_doc",
                  "_id" : "doc_2.pg_2",
                  "_score" : 0.14730778,
                  "_source" : {
                    "page" : 2,
                    "title" : "doc_2",
                    "content" : "... and the dog lept and got the fox"
                  },
                  "highlight" : {
                    "content" : [
                      "... and <em>the</em> dog lept and got <em>the</em> fox"
                    ]
                  }
                }
              ]
            }
          }
        }
      ]
    }
  }
}

Notice that the higher scoring document doc_2 is returned after doc_1, which is not what I want. I want to sort these results by the _score field in descending order, with the highest scoring title being returned first.

Can anyone help me out here? I feel like I'm very close to the answer.

Ok, I found the answer, thanks to this elastic blog . Here's the query I used:

GET my-index/_search
{ 
  "size" : 0,
  "track_total_hits": false,
  "query": {
    "simple_query_string": {
      "query": "the",
      "fields": ["content"]
    }
  },
  "aggs": {
    "top-ten-books": {
      "terms": {
        "field": "title",
            "size": 10,
            "order": {
              "max_score": "desc"
            }
          },
          "aggs": {
            "top-page": {
              "top_hits": {
                "size" : 1,
                "highlight": {"fields": {"content": {}}}
              }
            },
            "max_score" : {
              "max": {
                "script": "_score"
              }
            } 
          } 
    } 
  }
}

And here's the answer: this time with a properly sorted return!

{
  "took" : 4,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "top-ten-books" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "doc_2",
          "doc_count" : 2,
          "max_score" : {
            "value" : 0.14730778336524963
          },
          "top-page" : {
            "hits" : {
              "total" : {
                "value" : 2,
                "relation" : "eq"
              },
              "max_score" : 0.14730778,
              "hits" : [
                {
                  "_index" : "my-index",
                  "_type" : "_doc",
                  "_id" : "doc_2.pg_2",
                  "_score" : 0.14730778,
                  "_source" : {
                    "page" : 2,
                    "title" : "doc_2",
                    "content" : "... and the dog lept and got the fox"
                  },
                  "highlight" : {
                    "content" : [
                      "... and <em>the</em> dog lept and got <em>the</em> fox"
                    ]
                  }
                }
              ]
            }
          }
        },
        {
          "key" : "doc_1",
          "doc_count" : 2,
          "max_score" : {
            "value" : 0.10795845091342926
          },
          "top-page" : {
            "hits" : {
              "total" : {
                "value" : 2,
                "relation" : "eq"
              },
              "max_score" : 0.10795845,
              "hits" : [
                {
                  "_index" : "my-index",
                  "_type" : "_doc",
                  "_id" : "doc_1.pg_2",
                  "_score" : 0.10795845,
                  "_source" : {
                    "page" : 2,
                    "title" : "doc_1",
                    "content" : "... and the fox landed in a briar patch"
                  },
                  "highlight" : {
                    "content" : [
                      "... and <em>the</em> fox landed in a briar patch"
                    ]
                  }
                }
              ]
            }
          }
        }
      ]
    }
  }
}

I suspect you'll find field collapsing is a simpler solution

Mark_Harwood was right. Field collapsing was a much more elegant solution. This code also solves my problem:

GET my-index/_search
{
  "query": {"simple_query_string": {"query": "the", "fields": ["content"]}},
  "from": 0,
  "size": 10,
  "collapse" : {"field" : "title"},
  "sort": [{"_score": {"order": "desc"}}],
  "highlight": {"fields": {"content": {}}}
}

Here's the response:

{
  "took" : 848,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 4,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [
      {
        "_index" : "my-index",
        "_type" : "_doc",
        "_id" : "doc_2.pg_2",
        "_score" : 0.14730778,
        "_source" : {
          "page" : 2,
          "title" : "doc_2",
          "content" : "... and the dog lept and got the fox"
        },
        "fields" : {
          "title" : [
            "doc_2"
          ]
        },
        "highlight" : {
          "content" : [
            "... and <em>the</em> dog lept and got <em>the</em> fox"
          ]
        }
      },
      {
        "_index" : "my-index",
        "_type" : "_doc",
        "_id" : "doc_1.pg_2",
        "_score" : 0.10795845,
        "_source" : {
          "page" : 2,
          "title" : "doc_1",
          "content" : "... and the fox landed in a briar patch"
        },
        "fields" : {
          "title" : [
            "doc_1"
          ]
        },
        "highlight" : {
          "content" : [
            "... and <em>the</em> fox landed in a briar patch"
          ]
        }
      }
    ]
  }
}