ElasticSearch - query documents by term and field priority

Question

I'm currently working with elasticsearch and I'm trying to implement a query from the Java backend that will query documents from my index not only by term but by field priority as well. In my index, I have documents that have a term and a field that specifies a type.

e.g 
term: "Flu Shot"
type: "procedure"

term: "Fluphenazine"
type: "drug"

I created a query that will search by term and the elastic index will return the most relevant results matching that term. The functionality I want to create is to create a query to return results matching that same term but ordered by a priority of the 'type' field. For example when I type "flu" I want to get the documents with type: "procedure" first then after them the ones with the type "drug". Currently, the index returns only documents with type "drugs" due to many drugs that start with "flu".

narendra-choudhary · Accepted Answer · 2021-03-02 16:37:54Z

You can use function_score.

The function_score allows you to modify the score of documents that are retrieved by a query. To use function_score, the user has to define a query and one or more functions, that compute a new score for each document returned by the query.

Example your data in question (using Elasticsearch server 7.9):

Create index, and add documents

 PUT /example_index
 {
   "mappings": {
     "properties": {
       "term": {"type": "text" },
       "type": {"type": "keyword"}
     }
   }
 }

 PUT /_bulk
 {"create": {"_index": "example_index", "_id": 1}}
 {"term": "Flu Shot", "type": "procedure"}
 {"create": {"_index": "example_index", "_id": 2}}
 {"term": "Fluphenazine", "type": "drug"}
 {"create": {"_index": "example_index", "_id": 3}}
 {"term": "Flu Shot2", "type": "procedure"}
 {"create": {"_index": "example_index", "_id": 4}}
 {"term": "Fluphenazine2", "type": "drug"}

Query documents using custom scoring logic

 GET /example_index/_search
 {
   "query": {
     "function_score": {
       "query": {
         "wildcard": {
           "term": {
             "value": "*flu*"
           }
         }
       },
       "functions": [
         {
           "filter": {
             "term": {
               "type": "procedure"
             }
           },
           "weight": 2
         },
         {
           "filter": {
             "term": {
               "type": "drug"
             }
           },
           "weight": 1
         }
       ]
     }
   }
 }

Results:

 {
   "took" : 2,
   "timed_out" : false,
   "_shards" : {
     "total" : 1,
     "successful" : 1,
     "skipped" : 0,
     "failed" : 0
   },
   "hits" : {
     "total" : {
       "value" : 4,
       "relation" : "eq"
     },
     "max_score" : 2.0,
     "hits" : [
       {
         "_index" : "example_index",
         "_type" : "_doc",
         "_id" : "1",
         "_score" : 2.0,
         "_source" : {
           "term" : "Flu Shot",
           "type" : "procedure"
         }
       },
       {
         "_index" : "example_index",
         "_type" : "_doc",
         "_id" : "3",
         "_score" : 2.0,
         "_source" : {
           "term" : "Flu Shot2",
           "type" : "procedure"
         }
       },
       {
         "_index" : "example_index",
         "_type" : "_doc",
         "_id" : "2",
         "_score" : 1.0,
         "_source" : {
           "term" : "Fluphenazine",
           "type" : "drug"
         }
       },
       {
         "_index" : "example_index",
         "_type" : "_doc",
         "_id" : "4",
         "_score" : 1.0,
         "_source" : {
           "term" : "Fluphenazine2",
           "type" : "drug"
         }
       }
     ]
   }
 }

You can see the documents with type set to procedure have a higher score than the documents with type set to drug. This is because we've assigned different weights to the different types in the function_score.

This seems like a good solution if I'm using function score queries but what about term match queries? Especially ones that depend on a custom analyzer for the term? I've tried to wrap it in a bool/must query. It works for term + a type but what If I want to order two or more types by precedence order?

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