ElasticSearch Filter aggregation

Question

I need to return the number of children for each parent. That is my solution:

foreach (var person in someList)
{
  var countingFields = _elasticsearchClient.Search<SomeModel>(esModel=> esModel
                            .Aggregations(aggregation => aggregation
                                .Filter("Parents", filter => filter
                                    .Filter(innerFilter => innerFilter
                                        .Term(field => field.ParentId, person.Id))
                                    .Aggregations(innerAggregation => innerAggregation
                                        .ValueCount("Counting", count => count
                                            .Field(field => field.ParentId))))));
}

I need help to improve this, I want to get the same data with only one connection to ElasticSearch.

Rob · Accepted Answer · 2015-06-30 13:40:49Z

You can replace ValueCount with terms aggregation. So you will get result as:

ParentId Count
1        4
2        3

My test data set:

client.Index(new SomeModel {Id = 1, ParentId = 1});
client.Index(new SomeModel {Id = 2, ParentId = 2});
client.Index(new SomeModel {Id = 3, ParentId = 3});
client.Index(new SomeModel {Id = 4, ParentId = 1});

NEST terms aggregation syntax:

var someList = new List<int>{1,2,3,4};

var countingFields = client.Search<SomeModel>(esModel => esModel
    .Aggregations(aggregation => aggregation
        .Filter("Parents", filter => filter
            .Filter(innerFilter => innerFilter
                .Terms(field => field.ParentId, someList))
            .Aggregations(innerAggregation => innerAggregation
                .Terms("Counting", count => count
                    .Field(field => field.ParentId))))));

Response:

"aggregations": {
   "Parents": {
      "doc_count": 4,
      "Counting": {
         "doc_count_error_upper_bound": 0,
         "sum_other_doc_count": 0,
         "buckets": [
            {
               "key": 1,
               "doc_count": 2
            },
            {
               "key": 2,
               "doc_count": 1
            },
            {
               "key": 3,
               "doc_count": 1
            }
         ]
      }
   }
}

Hope it helps you.

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