Search the entire text of an `object` field in ElasticSearch - elasticsearch

Question

I have an ElasticSearch index which has an object property which stores some very dynamic JSON. I'd like to do full-text search on that JSON field. How do I index this field so that I can see if a certain word appears anywhere in the JSON, without knowing the exact key it will appear in, in advance? Like, is there a way to just index all leaf nodes of the JSON property? I'm on ElasticSearch 6.8 by the way, so I don't have the flattened field, which I think does this.
Index definition
PUT /test?include_type_name=true
{
"settings": {"number_of_shards": 1, "number_of_replicas": 1},
"mappings": {
"_doc": {
"_source": {"enabled": "true"},
"properties": {
"content": {
"type": "object",
"enabled": "true"
}
}
}
}
}
Document insertion
PUT /test/_doc/1
{
"content": {
"a": {
"b": {
"text": "42"
}
}
}
}
Query
GET /test/_search
{
"query": {
"match": {
"content": "42"
}
}
}
Response:
{
"took" : 1,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : 0,
"max_score" : null,
"hits" : [ ]
}
}

Answer 1

You're right, the flattened field type is what you need. But until your upgrade, you can do it using dynamic templates. In the mapping below, we match any string field inside the content object field to text and we also copy its value into another field called content_text that we're going to be able to search on:
PUT /test
{
"mappings": {
"dynamic_templates": [
{
"full_name": {
"match_mapping_type": "string",
"path_match": "content.*",
"mapping": {
"type": "text",
"copy_to": "content_text"
}
}
}
],
"properties": {
"content_text": {
"type": "text"
},
"content": {
"type": "object",
"enabled": "true"
}
}
}
}
Your sample document:
PUT /test/_doc/1
{
"content": {
"a": {
"b": {
"text": "42"
}
}
}
}
And now you can search on that new field as if you were searching on any field inside the content field:
GET /test/_search
{
"query": {
"match": {
"content_text": "42"
}
}
}