Elasticsearch unexpected results when sorting against deeply nested attributes - sorting

Question

I'm trying to perform some sorting based on the attributes of a document's deeply nested children.
Let's say we have an index filled with publisher documents. A publisher has a collection of books, and
each book has a title, a published flag, and a collection of genre scores. A genre_score represents how well
a particular book matches a particular genre, or in this case a genre_id.
First, let's define some mappings (for simplicity, we will only be explicit about the nested types):
curl -XPUT 'localhost:9200/book_index' -d '
{
"mappings": {
"publisher": {
"properties": {
"books": {
"type": "nested",
"properties": {
"genre_scores": {
"type": "nested"
}
}
}
}
}
}
}'
Here are our two publishers:
curl -XPUT 'localhost:9200/book_index/publisher/1' -d '
{
"name": "Best Books Publishing",
"books": [
{
"name": "Published with medium genre_id of 1",
"published": true,
"genre_scores": [
{ "genre_id": 1, "score": 50 },
{ "genre_id": 2, "score": 15 }
]
}
]
}'
curl -XPUT 'localhost:9200/book_index/publisher/2' -d '
{
"name": "Puffin Publishers",
"books": [
{
"name": "Published book with low genre_id of 1",
"published": true,
"genre_scores": [
{ "genre_id": 1, "score": 10 },
{ "genre_id": 4, "score": 10 }
]
},
{
"name": "Unpublished book with high genre_id of 1",
"published": false,
"genre_scores": [
{ "genre_id": 1, "score": 100 },
{ "genre_id": 2, "score": 35 }
]
}
]
}'
And here is the final definition of our index & mappings...
curl -XGET 'localhost:9200/book_index/_mappings?pretty=true'
...
{
"book_index": {
"mappings": {
"publisher": {
"properties": {
"books": {
"type": "nested",
"properties": {
"genre_scores": {
"type": "nested",
"properties": {
"genre_id": {
"type": "long"
},
"score": {
"type": "long"
}
}
},
"name": {
"type": "text",
"fields": {
"keyword": {
"type": "keyword",
"ignore_above": 256
}
}
},
"published": {
"type": "boolean"
}
}
},
"name": {
"type": "text",
"fields": {
"keyword": {
"type": "keyword",
"ignore_above": 256
}
}
}
}
}
}
}
}
Now suppose we want to query for a list of publishers, and have them sorted by those who books performing
well in a particular genre. In other words, sort the publishers by the genre_score.score of one of their books
for the target genre_id.
We might write a search query like this...
curl -XGET 'localhost:9200/book_index/_search?pretty=true' -d '
{
"size": 5,
"from": 0,
"sort": [
{
"books.genre_scores.score": {
"order": "desc",
"nested_path": "books.genre_scores",
"nested_filter": {
"term": {
"books.genre_scores.genre_id": 1
}
}
}
}
],
"_source":false,
"query": {
"nested": {
"path": "books",
"query": {
"bool": {
"must": []
}
},
"inner_hits": {
"size": 5,
"sort": []
}
}
}
}'
Which correctly returns the Puffin (with a sort value of [100]) first and Best Books second (with a sort value of [50]).
But suppose we only want to consider books for which published is true. This would change our expectation to have Best Books first (with a sort of [50]) and Puffin second (with a sort of [10]).
Let's update our nested_filter and query to the following...
curl -XGET 'localhost:9200/book_index/_search?pretty=true' -d '
{
"size": 5,
"from": 0,
"sort": [
{
"books.genre_scores.score": {
"order": "desc",
"nested_path": "books.genre_scores",
"nested_filter": {
"bool": {
"must": [
{
"term": {
"books.genre_scores.genre_id": 1
}
}, {
"term": {
"books.published": true
}
}
]
}
}
}
}
],
"_source": false,
"query": {
"nested": {
"path": "books",
"query": {
"term": {
"books.published": true
}
},
"inner_hits": {
"size": 5,
"sort": []
}
}
}
}'
Suddenly, our sort values for both publishers has become [-9223372036854775808].
Why does adding an additional term to our nested_filter in the top-level sort have this impact?
Can anyone provide some insight as to why this behavior is happening? And additionally, if there are any viable solutions to the proposed query/sort?
This occurs in both ES1.x and ES5
Thanks!