Elasticsearch sort by single nested document key in array

Question

I have documents which look like this (here are two examples): ``` { "id": 1234, "title": "the title", "body": "the body", "examples": [ { "evidence_source": "friend", "source_score": 15 }, { "evidence_source": "parent", "source_score": 12 } ] } ``` and ``` { "id": 6346, "title": "new title", "body": "lots of content", "examples": [ { "evidence_source": "friend", "source_score": 10 }, { "evidence_source": "parent", "source_score": 27 }, { "evidence_source": "child", "source_score": 4 } ] } ``` The format of the sub-documents in the `examples` array will always have an `evidence_source` and a `source_score` but there will be a variable amount of these sub-documents, each with different `evidence_source` values. I am wondering if it is possible to sort documents with this format based on one of the `source_score` values matched to a specific `evidence_source` value. I'd really like to be able to do this: - Sort documents by `source_score` descending where the related `evidence_source` i…

Accepted Answer

Support for sorting based on fields inside of nested documents was added to elasticsearch in 0.90:

https://github.com/elasticsearch/elasticsearch/issues/2662

The sorting by nested field support has the following parameters on top of the already existing sort options:

- `nested_path` - Defines the on what nested object to sort. The actual sort field must be a direct field inside this nested object. The default is to use the most immediate inherited nested object from the sort field.

- `nested_filter` - A filter the inner objects inside the nested path should match with in order for its field values to be taken into account by sorting. Common case is to repeat the query / filter inside the nested filter or query. By default no `nested_filter` is active.

Given your example data, the following query should give you what you're after:

```
{
  "query": {
    "match_all": {}
  },
  "sort": [
    {
      "examples.source_score": {
        "order": "desc",
        "nested_path": "examples",
        "nested_filter": {
          "term": {
            "examples.evidence_source": "friend"
          }
        }
      }
    }
  ]
}
```

Elasticsearch sort by single nested document key in array

Solution

Problem