How to aggregate over dynamic fields in elasticsearch?

Question

I am trying to aggregate over dynamic fields (different for different documents) via elasticsearch. Documents are like following:

[{
   "name": "galaxy note",
   "price": 123,
   "attributes": {
      "type": "phone",
      "weight": "140gm"
   }
},{
   "name": "shirt",
   "price": 123,
   "attributes": {
      "type": "clothing",
      "size": "m"
   }
}]

As you can see attributes change across documents. What Im trying to achieve is to aggregate fields of these attributes, like so:

{
     aggregations: {
         types: {
             buckets: [{key: 'phone', count: 123}, {key: 'clothing', count: 12}]
         }
     }
}

I am trying aggregation feature of elasticsearch to achieve this, but not able to find correct way. Is it possible to achieve via aggregation ? Or should I start looking in to facets, thought it seem to be depricated.

Answer 1

You have to define attributes as nested in your mapping and change the layout of the single attribute values to the fixed layout { key: DynamicKey, value: DynamicValue }

PUT /catalog
{
  "settings" : {
    "number_of_shards" : 1
  },
  "mappings" : {
    "article": {
      "properties": {
        "name": { 
          "type" : "string", 
          "index" : "not_analyzed" 
        },
        "price": { 
          "type" : "integer" 
        },
        "attributes": {
          "type": "nested",
          "properties": {
            "key": {
              "type": "string"
            },
            "value": {
              "type": "string"
            }
          }
        }
      }  
    }
  }
}

You may than index your articles like this

POST /catalog/article
{
  "name": "shirt",
  "price": 123,
  "attributes": [
    { "key": "type", "value": "clothing"},
    { "key": "size", "value": "m"}
  ]
}

POST /catalog/article
{
  "name": "galaxy note",
  "price": 123,
  "attributes": [
    { "key": "type", "value": "phone"},
    { "key": "weight", "value": "140gm"}
  ]
}

After all you are then able to aggregate over the nested attributes

GET /catalog/_search
{
  "query":{
    "match_all":{}
  },     
  "aggs": {
    "attributes": {
      "nested": {
        "path": "attributes"
      },
      "aggs": {
        "key": {
          "terms": {
            "field": "attributes.key"
          },
          "aggs": {
            "value": {
              "terms": {
                "field": "attributes.value"
              }
            }
          }
        }
      }
    }
  }
}

Which then gives you the information you requested in a slightly different form

[...]
"buckets": [
  {
    "key": "type",
    "doc_count": 2,
    "value": {
      "doc_count_error_upper_bound": 0,
      "sum_other_doc_count": 0,
      "buckets": [
      {
        "key": "clothing",
        "doc_count": 1
      }, {
        "key": "phone",
        "doc_count": 1
      }
      ]
    }
  },
[...]