ElasticSearch - Unable to filter on an array of strings - elasticsearch

Question

I have the following model class:
public class NewsItem
{
public String Language { get; set; }
public DateTime DateUpdated { get; set; }
public List<String> Tags { get; set; }
}
I index it with NEST using the automapping, resulting in the mapping below:
{
"search": {
"mappings": {
"news": {
"properties": {
"dateUpdated": {
"type": "date",
"format": "strict_date_optional_time||epoch_millis"
},
"language": {
"type": "string"
},
"tags": {
"type": "string"
},
}
}
}
}
}
I then run a query on language which works fine:
{
"query": {
"constant_score": {
"filter": [
{
"terms": {
"language": [
"en"
]
}
}
]
}
},
"sort": {
"dateUpdated": {
"order": "desc"
}
}
}
But running the same query on the tags property doesn't work. Is there any special tricks to query an array field? I read the docs again and again and I don't understand why this query gives no results:
{
"query": {
"constant_score": {
"filter": [
{
"terms": {
"tags": [
"Hillary"
]
}
}
]
}
},
"sort": {
"dateUpdated": {
"order": "desc"
}
}
}
The document returned from another query:
{
"_index": "search",
"_type": "news",
"_score": 0.12265198,
"_source": {
"tags": [
"Hillary"
],
"language": "en",
"dateUpdated": "2016-11-07T15:41:00Z"
}
}

Answer 1

Your tags field is analyzed, hence Hillary has been indexed to hillary. So you have two ways out:
A. Use a match query instead (since terms query does not analyze the token
{
"query": {
"bool": {
"filter": [
{
"match": { <--- use match here
"tags": "Hillary"
}
}
]
}
},
"sort": {
"dateUpdated": {
"order": "desc"
}
}
}
B. Keep the terms query but lowercase the token:
{
"query": {
"bool": {
"filter": [
{
"terms": {
"tags": [
"hillary" <--- lowercase here
]
}
}
]
}
},
"sort": {
"dateUpdated": {
"order": "desc"
}
}
}

Answer 2

Elasticsearch by default runs an analyzer on all strings but Terms filter on other hand computer exact match. So this implies that ES is storing 'Hillary' as 'hillary' while you are querying for 'Hillary'. So, there are 2 ways to fix this. Either you use a match query instead of terms query or you don't automap and rather create an index and analyze the tags field as you want. You can also query 'hillary' but this would be a solution for this one case because if tag was something like 'us elections' us and elections both will be stored separately.