How to use Nested Aggregation on Elasticsearch?

Question

I am pretty new to elasticsearch. I am writing a nested dsl using aggregation.

Structure of Input Document is something like this:

   {
        "_source": {
           "id": 1234,
           "oid": 6,

            "education": [
              {
                 "school_name": "Harvard",
                 "city" : "Boston",
                 "year": 1965,
                 "degree": "Undergrad"
              },
              {
                 "school_name": "Harvard",
                 "city" : "Boston",
                 "year": 1975,
                 "degree": "Masters"
              },
              {
                 "school_name": "Harvard",
                 "city" : "Boston",
                 "year": 1958,
                 "degree": "BA"
              }  
           ],
        }
     },

----Another records... and so on

*Above shown document complies to one record.

Goal: I am trying to find out all those students who studied in Boston. So Ideally if I have only above document then I should get only 1 record.

With the nested aggregation query I have written below I am getting 3 as a count for Boston

GET cluster_test/index_test/_search
{
"query": {
 "bool": {
  "must": [
    {
      "term": {
        "oid": {
          "value": "6"
        }
      }
    }
  ]
}
},
 "aggs": {
    "education": {
      "nested": {
        "path": "education"
      },
      "aggs": {
        "edu": {
          "terms": {
            "field": "education.city",
            "size": 0
          }
        }
      }
    }
  }
}         

If anyone can point out where I am going wrong or what is better to deal with these type of queries. Any help is appreciated.

Answer 1

You shouldn't be using aggregations as you want to filter students who studied on desired city. Using filters like below should help.

GET cluster_test/index_test/students/_search
{
"filtered" : {
    "query" : { "match_all" : {} },
    "filter" : {
        "nested" : {
            "path" : "education",
            "filter" : {
                "bool" : {
                    "must" : [
                        {
                            "term" : {"education.city" : "Boston"}
                        }
                    ]
                }
            }
        }
    }
}