Regular Expressions and Elastic Search - regex

Question

I am trying to retrieve some company results using elasticsearch. I want to get companies that start with "A", then "B", etc. If I just do a pretty typical query with "prefix" like so
GET apple/company/_search
{
"query": {
"prefix": {
"name": "a"
}
},
"fields": [
"id",
"name",
"websiteUrl"
],
"size": 100
}
But this will return Acme as well as Lemur and Associates, so I need to distinguish between A at the beginning of the whole name versus just A at the beginning of a word.
It would seem like regular expressions would come to the rescue here, but elastic search just ignores whatever I try. In tests with other applications, ^[\S]a* should get you anything that starts with A that doesn't have a space in front of it. Elastic search returns 0 results with the following:
GET apple/company/_search
{
"query": {
"regexp": {
"name": "^[\S]a*"
}
},
"fields": [
"id",
"name",
"websiteUrl"
],
"size": 100
}
In FACT, the Sense UI for Elasticsearch will immediately alert you to a "Bad String Syntax Error". That's because even in a query elastic search wants some characters escaped. Nonetheless ^[\\S]a* doesn't work either.

Answer 1

Searching in Elasticsearch is both about the query itself, but also about the modelling of your data so it suits best the query to be used. One cannot simply index whatever and then try to struggle to come up with a query that does something.
The Elasticsearch way for your query is to have the following mapping for that field:
PUT /apple
{
"settings": {
"index": {
"analysis": {
"analyzer": {
"keyword_lowercase": {
"type": "custom",
"tokenizer": "keyword",
"filter": [
"lowercase"
]
}
}
}
}
},
"mappings": {
"company": {
"properties": {
"name": {
"type": "string",
"fields": {
"analyzed_lowercase": {
"type": "string",
"analyzer": "keyword_lowercase"
}
}
}
}
}
}
}
And to use this query:
GET /apple/company/_search
{
"query": {
"prefix": {
"name.analyzed_lowercase": {
"value": "a"
}
}
}
}
or
GET /apple/company/_search
{
"query": {
"query_string": {
"query": "name.analyzed_lowercase:A*"
}
}
}