Elasticsearch: search/order by overall tag weight

Question

I have to solve a problem that exeeds my very basic knowhow of elasticsearch.

I have a set of objects - each one has a set of tags. Like:

obj_1 = ["a", "b", "c"]
obj_2 = ["a", "b"]
obj_3 = ["c", "b"]

I want to search the objects using weighted tags. For example:

search_tags = {'a': 1.0, 'c': 1.5}

I want the search tags to be an OR query. That is - I don't want to exclude documents that don't have all of the queried tags. But I want them to be ordered by the one that has the most weight (sort of: each matched tag multiplied by its weight).

Using the example above the order of the ducuments returned would be:

• obj_1 (score: 1.0+1.5)
• obj_3 (score: 1.5)
• obj_2 (score: 1.0)

What would be the best approach to this regarding the document's structure and the correct way to query ES?

There is a similar question here: Elastic search - tagging strength (nested/child document boosting) only that I do not want to specify the weight when indexing - I want it done when searching.

My current setup is as follows.

The objects:

[
   "title":"1", "tags" : ["a", "b", "c"],
   "title":"2", "tags" : ["a", "b"],
   "title":"3", "tags" : ["c", "b"],
   "title":"4", "tags" : ["b"]
]

And my query:

{ 
    "query": {
        "custom_filters_score": {
            "query": { 
                "terms": {
                    "tags": ["a", "c"],
                    "minimum_match": 1
                }
            },
            "filters": [
                {"filter":{"term":{"tags":"a"}}, "boost":1.0},    
                {"filter":{"term":{"tags":"c"}}, "boost":1.5}    
            ],
            "score_mode": "total"
        }
    }
}

The problem is that it only returns object 1 and 3. It should match object 2 (has tag "a") as well, or am I doing something wrong?

UPDATE AS SUGGESTED

Ok. Changed boost to script to calculate the minimum. Removed minimum match. My request:

{
    "query": {
        "custom_filters_score": {
            "query": {
                "terms": {
                    "tags": ["a", "c"]
                }
            },
            "filters": [
                {"filter":{"term":{"tags":"a"}}, "script":"1.0"},
                {"filter":{"term":{"tags":"c"}}, "script":"1.5"}
            ],
            "score_mode": "total"
        }
    }
}

Response:

{
    "_shards": {
        "failed": 0,
        "successful": 5,
        "total": 5
    },
    "hits": {
        "hits": [
            {
                "_id": "3",
                "_index": "test",
                "_score": 0.23837921,
                "_source": {
                    "tags": [
                        "c",
                        "b"
                    ],
                    "title": "3"
                },
                "_type": "bit"
            },
            {
                "_id": "1",
                "_index": "test",
                "_score": 0.042195037,
                "_source": {
                    "tags": [
                        "a",
                        "b",
                        "c"
                    ],
                    "title": "1"
                },
                "_type": "bit"
            }
        ],
        "max_score": 0.23837921,
        "total": 2
    },
    "timed_out": false,
    "took": 3
}

Still getting wrong order and one result missing. obj_1 should be before obj_3 (because it has both tags) and obj_2 is still missing completely. How can this be?

Answer 1

There were 2 problems with my example.

1. The "a" term is a stopword so it was discarded and only "c" term was being used.
2. The custom_filters_score query has to include "constant_score" query so that all terms have the same weight before boosting.

Now it works!