Filter nested objects in ElasticSearch 6.8.1

Question

I didn't find any answers how to do simple thing in ElasticSearch 6.8 I need to filter nested objects.

Index

{
  "settings": {
    "index": {
      "number_of_shards": "5",
      "number_of_replicas": "1"
    }
  },
  "mappings": {
    "human": {
      "properties": {
        "cats": {
          "type": "nested",
          "properties": {
            "name": {
              "type": "text"
            },
            "breed": {
              "type": "text"
            },
            "colors": {
              "type": "integer"
            }
          }
        },
        "name": {
          "type": "text"
        }
      }
    }
  }
}

Data

{
  "name": "iridakos",
  "cats": [
    {
      "colors": 1,
      "name": "Irida",
      "breed": "European Shorthair"
    },
    {
      "colors": 2,
      "name": "Phoebe",
      "breed": "european"
    },
    {
      "colors": 3,
      "name": "Nino",
      "breed": "Aegean"
    }
  ]
}

select human with name="iridakos" and cats with breed contains 'European' (ignore case). Only two cats should be returned.

Million thanks for helping.

Kamal Kunjapur · Accepted Answer · 2020-03-20 19:02:46Z

For nested datatypes, you would need to make use of nested queries.

Elasticsearch would always return the entire document as a response. Note that nested datatype means that every item in the list would be treated as an entire document in itself.

Hence in addition to return entire document, if you also want to know the exact hits, you would need to make use of inner_hits feature.

Below query should help you.

POST <your_index_name>/_search
{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "name": "iridakos"
          }
        },
        {
          "nested": {
            "path": "cats",
            "query": {
              "match": {
                "cats.breed": "european"
              }
            },
            "inner_hits": {}
          }
        }
      ]
    }
  }
}

Response:

{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 0.74455214,
    "hits" : [
      {
        "_index" : "my_cat_index",
        "_type" : "_doc",
        "_id" : "1",                           <--- The document that hit
        "_score" : 0.74455214,
        "_source" : {
          "name" : "iridakos",
          "cats" : [
            {
              "colors" : 1,
              "name" : "Irida",
              "breed" : "European Shorthair"
            },
            {
              "colors" : 2,
              "name" : "Phoebe",
              "breed" : "european"
            },
            {
              "colors" : 3,
              "name" : "Nino",
              "breed" : "Aegean"
            }
          ]
        },
        "inner_hits" : {                       <---- Note this
          "cats" : {
            "hits" : {
              "total" : {
                "value" : 2,                   <---- Count of nested doc hits
                "relation" : "eq"
              },
              "max_score" : 0.52354836,
              "hits" : [
                {
                  "_index" : "my_cat_index",
                  "_type" : "_doc",
                  "_id" : "1",
                  "_nested" : {
                    "field" : "cats",
                    "offset" : 1
                  },
                  "_score" : 0.52354836,
                  "_source" : {                       <---- First Nested Document 
                    "breed" : "european"              
                  }
                },
                {
                  "_index" : "my_cat_index",
                  "_type" : "_doc",
                  "_id" : "1",
                  "_nested" : {
                    "field" : "cats",
                    "offset" : 0
                  },
                  "_score" : 0.39019167,
                  "_source" : {                       <---- Second Document
                    "breed" : "European Shorthair"
                  }
                }
              ]
            }
          }
        }
      }
    ]
  }
}

Note in your response how the inner_hits section would appear where you would find the exact hits.

Hope this helps!

TheDude · Accepted Answer · 2020-03-20 14:57:27Z

0

You could use something like this:

{
  "query": { 
    "bool": { 
      "must": [
        { "match": { "name":   "iridakos" }},
        { "match": { "cats.breed": "European" }}
      ]
    }
  }
}

To search on a cat's breed, you can use the dot-notation.

answered Mar 20, 2020 at 14:57

TheDude

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3 Comments

boris_dev Over a year ago

Thank you for answer. But how to filter nested cats? I need to return only 2 nested "cats" in parent "human" object

Kamal Kunjapur Over a year ago

This is incorrect. And doesn't work. Notice the datatype of cats, it is nested and not object type.

TheDude Over a year ago

@boris_dev looks like you can use a "nested" query like in here elastic.co/guide/en/elasticsearch/reference/current/…

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