How to highlight characters within words using elasticsearch - elasticsearch

Question

I have implemented auto suggest using elastic search where I am giving suggestions to users based on typed value 'where'. Most of the part works fine if I type full word or few starting characters of word. I want to highlight specific characters typed by the user, say for example user types 'ca' then suggestions should highlight 'California' only and not whole word 'California'
Highlight tag should show result like <b>Ca</b>lifornia and not <b>California</b>.
Here is my index settings
{
"settings": {
"index": {
"analysis": {
"filter": {
"edge_filter": {
"type": "edge_ngram",
"min_gram": 1,
"max_gram": 50
},
"lowercase_filter":{
"type":"lowercase",
"language": "greek"
},
"metro_synonym": {
"type": "synonym",
"synonyms_path": "metro_synonyms.txt"
},
"profession_specialty_synonym": {
"type": "synonym",
"synonyms_path": "profession_specialty_synonyms.txt"
}
},
"analyzer": {
"auto_suggest_analyzer": {
"filter": [
"lowercase",
"edge_filter"
],
"type": "custom",
"tokenizer": "whitespace"
},
"auto_suggest_search_analyzer": {
"filter": [
"lowercase"
],
"type": "custom",
"tokenizer": "whitespace"
},
"lowercase": {
"filter": [
"trim",
"lowercase"
],
"type": "custom",
"tokenizer": "keyword"
}
}
}
}
},
"mappings": {
"properties": {
"what_auto_suggest": {
"type": "text",
"analyzer": "auto_suggest_analyzer",
"search_analyzer": "auto_suggest_search_analyzer",
"fields": {
"raw":{
"type":"keyword"
}
}
},
"company": {
"type": "text",
"analyzer": "lowercase"
},
"where_auto_suggest": {
"type": "text",
"analyzer": "auto_suggest_analyzer",
"search_analyzer": "auto_suggest_search_analyzer",
"fields": {
"raw":{
"type":"keyword"
}
}
},
"tags_auto_suggest": {
"type": "text",
"analyzer": "auto_suggest_analyzer",
"search_analyzer": "auto_suggest_search_analyzer",
"fields": {
"raw":{
"type":"keyword"
}
}
}
}
}
}
Query i am using to pull suggestions -
GET /autosuggest_index_test/_search
{
"query": {
"bool": {
"must": [
{
"match": {
"where_auto_suggest": {
"query": "ca",
"operator": "and"
}
}
}
]
}
},
"aggs": {
"NAME": {
"terms": {
"field": "where_auto_suggest.raw",
"size": 10
}
}
},
"highlight": {
"pre_tags": [
"<b>"
],
"post_tags": [
"</b>"
],
"fields": {
"where_auto_suggest": {
}
}
}
}
One of json result that I am getting -
{
"_index" : "autosuggest_index_test",
"_type" : "_doc",
"_id" : "Calabasas CA",
"_score" : 5.755663,
"_source" : {
"where_auto_suggest" : "Calabasas CA"
},
"highlight" : {
"where_auto_suggest" : [
"<b>Calabasas</b> <b>CA</b>"
]
}
}
Can someone please suggest, how to get output here (in the where_auto_suggest) like - "<b>Ca</b>labasas <b>CA</b>"

Answer 1

I don't really know why but if you use a edge_ngram tokenizer instead of an edge_ngram filter you will have highlighted characters instead of highlighted words.
So in your settings, you could declare such a tokenizer :
"settings": {
"index": {
"analysis": {
"tokenizer": {
"edge_tokenizer": {
"type": "edge_ngram",
"min_gram": 1,
"max_gram": 50,
"token_chars": [
"letter",
"digit",
"punctuation",
"symbol"
]
}
},
...
}
}
}
And change your analyzer to :
"analyzer": {
"auto_suggest_analyzer": {
"filter": [
"lowercase"
],
"type": "custom",
"tokenizer": "edge_tokenizer"
}
...
}
Thus your example request will return
{
...
"hits": {
"total": {
"value": 1,
"relation": "eq"
},
"max_score": 0.2876821,
"hits": [
{
"_index": "autosuggest_index_test",
"_type": "_doc",
"_id": "grIzo28BY9R4-IxJhcFv",
"_score": 0.2876821,
"_source": {
"where_auto_suggest": "california"
},
"highlight": {
"where_auto_suggest": [
"<b>ca</b>lifornia"
]
}
}
]
}
...
}