More Like This queries return 0 results if field in source document has 0 tokens in analyzed field #30148
Description
Elasticsearch version: 6.2.4
Plugins installed: []
JVM version: 1.8.0_101
OS version: MacOS (Darwin Kernel Version 15.6.0)
Description of the problem including expected versus actual behavior:
"More Like This" queries do not return any results when a field on the source document produces no tokens at index time. Using a keyword field and manually specifying the analyzer at query time works as expected.
Steps to reproduce:
PUT test
{
"mappings": {
"type": {
"properties": {
"myField": {
"type": "text"
},
"empty": {
"type": "text"
}
}
}
}
}
POST /_bulk
{ "index": { "_index": "test", "_type": "type","_id":1}}
{"myField":"and_foo", "empty":""}
{ "index": { "_index": "test", "_type": "type","_id":2}}
{"myField":"and_foo", "empty":""}
This query correctly returns 1 result:
GET /_search
{
"query": {
"more_like_this": {
"fields": [
"myField"
],
"like": [
{
"_index": "test",
"_type": "type",
"_id": "1"
}
],
"min_term_freq": 1,
"min_doc_freq": 1
}
}
}
This query returns no results when using both fields:
GET /_search
{
"query": {
"more_like_this": {
"fields": [
"myField", "empty"
],
"like": [
{
"_index": "test",
"_type": "type",
"_id": "1"
}
],
"min_term_freq": 1,
"min_doc_freq": 1
}
}
}
If you update the "empty" field in document 1 to contain non-analyzable characters (like punctuation), the first query still gives 0 results. Changing the "empty" field to be a keyword field works as expected.