Sort nested object in Elasticsearch - elasticsearch

Question

I'm using the following mapping:
PUT /my_index
{
"mappings": {
"blogpost": {
"properties": {
"title": {"type": "string"}
"comments": {
"type": "nested",
"properties": {
"comment": { "type": "string" },
"date": { "type": "date" }
}
}
}
}
}
}
Example of document:
PUT /my_index/blogpost/1
{
"title": "Nest eggs",
"comments": [
{
"comment": "Great article",
"date": "2014-09-01"
},
{
"comment": "More like this please",
"date": "2014-10-22"
},
{
"comment": "Visit my website",
"date": "2014-07-02"
},
{
"comment": "Awesome",
"date": "2014-08-23"
}
]
}
My question is how to retrieve this document and sort the nested object "comments" by "date"? the result:
PUT /my_index/blogpost/1
{
"title": "Nest eggs",
"comments": [
{
"comment": "Awesome",
"date": "2014-07-23"
},
{
"comment": "Visit my website",
"date": "2014-08-02"
},
{
"comment": "Great article",
"date": "2014-09-01"
},
{
"comment": "More like this please",
"date": "2014-10-22"
}
]
}

Answer 1

You need to sort on the inner_hits to sort the nested objects. This will give you the desired output
GET my_index/_search
{
"query": {
"nested": {
"path": "comments",
"query": {
"match_all": {}
},
"inner_hits": {
"sort": {
"comments.date": {
"order": "asc"
}
},
"size": 5
}
}
},
"_source": [
"title"
]
}
I am using source filtering to get only "title" as comments will be retrieved inside inner_hit but you can avoid that if you want
size is 5 because default value is 3 and we have 4 objects in the given example.
Hope this helps!