I am using the Java API for elasticsearch and I am trying to get only the last version (which is a custom field) of each document when executing a search.

For example :

{ id: 1, name: "John Greenwood", version: 1}
{ id: 1, name: "John Greenwood", version: 2}
{ id: 2, name: "John Underwood", version: 1}

While searching with Jhon, I want this result :

{ id: 1, name: "John Greenwood", follower_count: 2}
{ id: 2, name: "John Underwood", follower_count: 1}

Apparently I am supposed to use aggregation, but Im not sure how to use them with the Java API. Also, how can I regroup the documents with the ID also ? Because I only want the latest version for the same ID

CodePudding user response：

Tldr;

Yes, you are on the right track.

You will want to aggregate on the id of each user. The get the top_hit per regard to the version.

Solution

The first aggregation per_id is grouping user by their id, then inside this aggregation we perform another one. lastest_version that is going to select the best hit with regards to the version. I select the size: 1 to get a top 1 per group.

GET 74550367/_search
{
  "query": {
    "match_all": {}
  },
  "aggs": {
    "per_id": { 
      "terms": {
        "field": "id"
      },
      "aggs": {
        "lastest_version": {
          "top_hits": {
            "sort": [
              {
                "version": {
                  "order": "desc"
                }
              }
            ],
            "size": 1
          }
        }
      }
    }
  }
}

To Reproduce

POST _bulk
{ "index": {"_index":"74550367"}}
{ "id": 1, "name": "John Greenwood", "version": 1}
{ "index": {"_index":"74550367"}}
{ "id": 1, "name": "John Greenwood", "version": 2}
{ "index": {"_index":"74550367"}}
{ "id": 2, "name": "John Underwood", "version": 1}