Adding support for `fields` option in search query.

[mattjanssen]

The fields options for limiting a search response was introduced in version 7.10 and is documented here.

If I were to create a PR, would it be as simple as updating the ONGR\ElasticsearchDSL\Search class? Thanks!

[hkulekci]

Hello @mattjanssen, I guess this also needs support for both versions 8.x and 7.x. I'm happy to help you if you need support or a review for PR.

While implementation, let's think about the inner_hits too. Here is a sample using fields with inner_hits :

PUT sample
{
  "mappings": {
    "properties": {
      "users": {
        "type": "nested"
      }
    }
  }
}

POST sample/_doc
{
  "id": 3,
  "users": [
    {
      "id": 1,
      "name": "Foo 1"
    },
    {
      "id": 2,
      "name": "Foo 2"
    },
    {
      "id": 3,
      "name": "Foo 4"
    }
  ]
}

GET sample/_search
{
  "_source": ["id"], 
  "query": {
    "nested": {
      "path": "users",
      "inner_hits": {
        "fields": ["users.id", "users.name"]
      }, 
      "query": {
        "term": {
          "users.id": {
            "value": "1"
          }
        }
      }
    }
  }
}