Elastic exact match w/o changing indexing - elasticsearch

Question

I have following query to elastic:
"query": {
"filtered": {
"filter": {
"and": {
"filters": [
{
"term": {
"entities.hashtags": "gf"
}
}
]
}
},
"query": {
"match_phrase": {
"body": "anime"
}
}
}
},
entities.hashtags is array and as a result I receive entries with hashtags gf_anime, gf_whatever, gf_foobar etc.
But what I need is receive entries where exact "gf" hashtag exists.
I've looked in other questions on SO and saw that the solution in this case is to change analyzing of entities.hashtags so it'll match only exact values (I am pretty new with elastic hence can mistake with terms here).
My question is whether it's possible to define exact match search INSIDE THE QUERY? Id est w/o changing how elastic indexes its fields?

Answer 1

Are you sure that you need to do anything? Given your examples, you don't and you probably don't want to do not_analyzed:
curl -XPUT localhost:9200/test -d '{
"mappings": {
"test" : {
"properties": {
"body" : { "type" : "string" },
"entities" : {
"type" : "object",
"properties": {
"hashtags" : {
"type" : "string"
}
}
}
}
}
}
}'
curl -XPUT localhost:9200/test/test/1 -d '{
"body" : "anime", "entities" : { "hashtags" : "gf_anime" }
}'
curl -XPUT localhost:9200/test/test/2 -d '{
"body" : "anime", "entities" : { "hashtags" : ["GF", "gf_anime"] }
}'
curl -XPUT localhost:9200/test/test/3 -d '{
"body" : "anime", "entities" : { "hashtags" : ["gf_whatever", "gf_anime"] }
}'
With the above data indexed, your query only returns document 2 (note: this is simplified version of your query without the unnecessary/undesirable and filter; at least for the time being, you should always use the bool filter rather than and/or as it understands how to use the filter caches):
curl -XGET localhost:9200/test/_search
{
"query": {
"filtered": {
"filter": {
"term": {
"entities.hashtags": "gf"
}
},
"query": {
"match_phrase": {
"body": "anime"
}
}
}
}
}
Where this breaks down is when you start putting in hashtag values that will be split into multiple tokens, thereby triggering false hits with the term filter. You can determine how the field's analyzer will treat any value by passing it to the _analyze endpoint and telling it the field to use the analyzer from:
curl -XGET localhost:9200/test/_analyze?field=entities.hashtags\&pretty -d 'gf_anime'
{
"tokens" : [ {
"token" : "gf_anime",
"start_offset" : 0,
"end_offset" : 8,
"type" : "<ALPHANUM>",
"position" : 1
} ]
}
# Note the space instead of the underscore:
curl -XGET localhost:9200/test/_analyze?field=entities.hashtags\&pretty -d 'gf anime'
{
"tokens" : [ {
"token" : "gf",
"start_offset" : 0,
"end_offset" : 2,
"type" : "<ALPHANUM>",
"position" : 1
}, {
"token" : "anime",
"start_offset" : 3,
"end_offset" : 8,
"type" : "<ALPHANUM>",
"position" : 2
} ]
}
If you were to add a fourth document with the "gf anime" variant, then you will get a false hit.
curl -XPUT localhost:9200/test/test/4 -d '{
"body" : "anime", "entities" : { "hashtags" : ["gf whatever", "gf anime"] }
}'
This is really not an indexing problem, but a bad data problem.
With all of the explanation out of the way, you can inefficiently solve this by using a script that always follows the term filter (to efficiently rule out the more common cases that don't hit it):
curl -XGET localhost:9200/test/_search
{
"query": {
"filtered": {
"filter": {
"bool" : {
"must" : [{
"term" : {
"entities.hashtags" : "gf"
}
},
{
"script" : {
"script" :
"_source.entities.hashtags == tag || _source.entities.hashtags.find { it == tag } != null",
"params" : {
"tag" : "gf"
}
}
}]
}
},
"query": {
"match_phrase": {
"body": "anime"
}
}
}
}
}
This works by parsing the original the _source (and not using the indexed doc values). That is why this is not going to be very efficient, but it will work until you reindex. The _source.entities.hashtags == tag portion is only necessary if hashtags is not always an array (in my example, document 1 would not be an array). If it is always an array, then you can use _source.entities.hashtags.contains(tag) instead of _source.entities.hashtags == tag || _source.entities.hashtags.find { it == tag } != null.
Note: The script language is Groovy, which is the default starting in 1.4.0. It is not the default in earlier versions, and it must be explicitly enabled using script.default_lang : groovy.