Mixing exact search with stemmingedit
When building a search application, stemming is often a must as it is desirable
for a query on skiing to match documents that contain ski or skis. But
what if a user wants to search for skiing specifically? The typical way to do
this would be to use a multi-field in order to have the same
content indexed in two different ways:
PUT index
{
"settings": {
"analysis": {
"analyzer": {
"english_exact": {
"tokenizer": "standard",
"filter": [
"lowercase"
]
}
}
}
},
"mappings": {
"properties": {
"body": {
"type": "text",
"analyzer": "english",
"fields": {
"exact": {
"type": "text",
"analyzer": "english_exact"
}
}
}
}
}
}
PUT index/_doc/1
{
"body": "Ski resort"
}
PUT index/_doc/2
{
"body": "A pair of skis"
}
POST index/_refresh
With such a setup, searching for ski on body would return both documents:
GET index/_search
{
"query": {
"simple_query_string": {
"fields": [ "body" ],
"query": "ski"
}
}
}
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"skipped" : 0,
"failed": 0
},
"hits": {
"total" : {
"value": 2,
"relation": "eq"
},
"max_score": 0.18232156,
"hits": [
{
"_index": "index",
"_type": "_doc",
"_id": "1",
"_score": 0.18232156,
"_source": {
"body": "Ski resort"
}
},
{
"_index": "index",
"_type": "_doc",
"_id": "2",
"_score": 0.18232156,
"_source": {
"body": "A pair of skis"
}
}
]
}
}
On the other hand, searching for ski on body.exact would only return
document 1 since the analysis chain of body.exact does not perform
stemming.
GET index/_search
{
"query": {
"simple_query_string": {
"fields": [ "body.exact" ],
"query": "ski"
}
}
}
{
"took": 1,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"skipped" : 0,
"failed": 0
},
"hits": {
"total" : {
"value": 1,
"relation": "eq"
},
"max_score": 0.8025915,
"hits": [
{
"_index": "index",
"_type": "_doc",
"_id": "1",
"_score": 0.8025915,
"_source": {
"body": "Ski resort"
}
}
]
}
}
This is not something that is easy to expose to end users, as we would need to have a way to figure out whether they are looking for an exact match or not and redirect to the appropriate field accordingly. Also what to do if only parts of the query need to be matched exactly while other parts should still take stemming into account?
Fortunately, the query_string and simple_query_string queries have a feature
that solves this exact problem: quote_field_suffix. This tells Elasticsearch
that the words that appear in between quotes are to be redirected to a different
field, see below:
GET index/_search
{
"query": {
"simple_query_string": {
"fields": [ "body" ],
"quote_field_suffix": ".exact",
"query": "\"ski\""
}
}
}
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"skipped" : 0,
"failed": 0
},
"hits": {
"total" : {
"value": 1,
"relation": "eq"
},
"max_score": 0.8025915,
"hits": [
{
"_index": "index",
"_type": "_doc",
"_id": "1",
"_score": 0.8025915,
"_source": {
"body": "Ski resort"
}
}
]
}
}
In the above case, since ski was in-between quotes, it was searched on the
body.exact field due to the quote_field_suffix parameter, so only document
1 matched. This allows users to mix exact search with stemmed search as they
like.
If the choice of field passed in quote_field_suffix does not exist
the search will fall back to using the default field for the query string.