Truncate and Index String values in Elasticsearch 2.3.x - elasticsearch

Question

I am running ES 2.3.3. I want to index a non-analyzed String but truncate it to a certain number of characters. The ignore_above property, according to the documentation, will NOT index a field above the provided value. I don't want that. I want to take say a field that could potentially be 30K long and truncate it to 10K long, but still be able to filter and sort on the 10K that is retained.
Is this possible in ES 2.3.3 or do I need to do this using Java prior to indexing a document.

Answer 1

I want to index a non-analyzed String but truncate it to a certain number of characters.
Technically it's possible with Update API and Upsert option, but, depending on your exact needs, it may not be very handy.
Let's say you want to index this document:
{
"name": "foofoofoofoo",
"age": 29
}
but you need to truncate name field so that it has only 5 characters. Using Update API, you'd have to execute a script:
POST http://localhost:9200/insert/test/1/_update
{
"script" : "ctx._source.name = ctx._source.name.substring(0,5);",
"scripted_upsert": true,
"upsert" : {
"name": "foofoofoofoo",
"age": 29
}
}
It means that, if ES does not find the document with given id (here id=1), it should index the document that is inside upsert element, and perform given script. So as you can see, it's rather inconvenient if you want to have automatically generated ids, as you have to provide the id in URI.
Result:
GET http://localhost:9200/insert/test/1
{
"_index": "insert",
"_type": "test",
"_id": "1",
"_version": 1,
"found": true,
"_source": {
"name": "foofo",
"age": 29
}
}