Partial search on date fields in elasticsearch - elasticsearch

Question

I'm trying to implement partial search on a date field in elastic search. For example if startDate is stored as "2019-08-28" i should be able to retrieve the same while querying just "2019" or "2019-08" or "2019-0".
For other fields i'm doing this:
{
"simple_query_string": {
"fields": [
"customer"
],
"query": "* Andrew *",
"analyze_wildcard": "true",
"default_operator": "AND"
}}
which perfectly works on text fields, but the same doesn't work on date fields.
This is the mapping :
{"mappings":{"properties":{"startDate":{"type":"date"}}}}
Any way this can be achieved, be it change in mapping or other query method? Also i found this discussion related to partial dates in elastic, not sure if it's much relevant but here it is:
https://github.com/elastic/elasticsearch/issues/45284

Answer 1

Excerpt from ES-Docs
Internally, dates are converted to UTC (if the time-zone is specified)
and stored as a long number representing milliseconds-since-the-epoch.
It is not possible to do searching as we can do on a text field. However, we can tell ES to index date field as both date & text.e.g
Index date field as multi-type:
PUT sample
{
"mappings": {
"properties": {
"my_date": {
"type": "date",
"format": "year_month_day",//<======= yyyy-MM-dd
"fields": {
"formatted": {
"type": "text", //<========= another representation of type TEXT, can be accessed using my_date.formatted
"analyzer": "whitespace" //<======= whitespace analyzer (standard will tokenized 2020-01-01 into 2020,01 & 01)
}
}
}
}
}
}
POST dates/_doc
{
"date":"2020-01-01"
}
POST dates/_doc
{
"date":"2019-01-01"
}
Use wildcard query to search: You can even use n-grams at indexing time for faster search if required.
GET dates/_search
{
"query": {
"wildcard": {
"date.formatted": {
"value": "2020-0*"
}
}
}
}