Elasticsearch script sort on nested field

Question

I have the following type in elasticsearch

"hotel" : {
   "magicScore" : 1
   "rooms" : [
        {
       "type" : "single",
       "magicScore" : 1
        }, 
        {
        "type" : "double",
        "magicScore" : 2
        }
    ]
}

where rooms is of type nested. I would like to sort using a scripted sort, for example

 "sort" : [ {
    "_script" : {
      "script" : "return doc['magicScore'].value + doc['rooms.magicScore'].value",
       "params" :  ,
      "type" : "number",
      "reverse" : true
    }
  } ]

This does not work because rooms are nested objects, is there a way around this?

Swiety · Accepted Answer · 2019-06-28 22:13:20Z

3

Elasticsearch allows Script Based Sorting and Sorting within nested objects, more over you can mix both approaches together. You could try something like:

"sort" : [ {
   "_script" : {
      "nested": {
         "path": "rooms"
      },
      "script" : "return doc['magicScore'].value + doc['rooms.magicScore'].value",
      "params" :  ,
      "type" : "number",
      "reverse" : true
}}]

Once the nested path is specified, elasticsearch would lookup the terms of referred nested documents if those are indexed, so it would be possible to refer to them through the doc map. This would avoid the need to load the whole _source.

answered Jun 28, 2019 at 22:13

Swiety

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2 Comments

Jay Patel Over a year ago

I'm facing similar problem but while trying to sort using the script, I'm getting RequestError: RequestError(400, u'x_content_parse_exception', u'[1:29] [_script] failed to parse field [type]')

Harshit Over a year ago

This answer absolutely deserves an upvote!

keety · Accepted Answer · 2015-08-30 02:51:19Z

2

As per the documentation:

doc[...] notation only allows for simple valued fields (can’t return a json object from it) and makes sense only on non-analyzed or single term based fields.

You would need to use access it via the _source field

Something on these lines:

   "sort": [
      {
         "_script": {
            "script": "m=doc['magicScore'].value;for(obj in _source.rooms){ m += obj.magicScore;};return m;",
            "type": "number",
            "reverse": true
         }
      }
   ]

answered Aug 30, 2015 at 2:51

keety

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2 Comments

m1416 Over a year ago

hey, sorry for taking a while to reply. What you wrote works and ill accept it as answer. I had a huge performance hit because my documents are large. I ended up using a function_score query in java it would be something like QueryBuilders .nestedQuery("rooms", QueryBuilders.functionScoreQuery(filterBuilder, ScoreFunctionBuilders.scriptFunction() .param("values", values)) ).scoreMode("max")

m1416 Over a year ago

The next step for a future refactoring would be to use a bool query so i can access both the fields from the parent object and the nested object. The functionscorequery inside the nestedquery can only see fields from the nested documents. I had to put the magicScore field inside the nested documents for the whole thing to work

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