Elasticsearch group and order by nested field's min value - sorting

Question

I've got a structure of products which are available in different stores with different prices:
[{
"name": "SomeProduct",
"store_prices": [
{
"store": "FooStore1",
"price": 123.45
},
{
"store": "FooStore2",
"price": 345.67
}
]
},{
"name": "OtherProduct",
"store_prices": [
{
"store": "FooStore1",
"price": 456.78
},
{
"store": "FooStore2",
"price": 234.56
}
]
}]
I want to show a list of products, ordered by the lowest price ascending, limited to 10 results, in this way:
SomeProduct: 123.45 USD
OtherProduct: 234.56 USD
How to do this? I've tried the nested aggregation approach described in https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-nested-aggregation.html but it only returns the min price of all products, not the respective min price for each product:
{
"_source": [
"name",
"store_prices.price"
],
"query": {
"match_all": {}
},
"sort": {
"store_prices.price": "asc"
},
"aggs": {
"stores": {
"nested": {
"path": "store_prices"
},
"aggs": {
"min_price": {"min": {"field": "store_prices.price"}}
}
}
},
"from": 0,
"size": 10
}
In SQL, what I want to do could be described using the following query. I'm afraid I'm thinking too much "in sql":
SELECT
p.name,
MIN(s.price) AS price
FROM
products p
INNER JOIN
store_prices s ON s.product_id = p.id
GROUP BY
p.id
ORDER BY
price ASC
LIMIT 10

Answer 1

You need a nested sorting:
{
"query": // HERE YOUR QUERY,
"sort": {
"store_prices.price": {
"order" : "asc",
"nested_path" : "store_prices",
"nested_filter": {
// HERE THE FILTERS WHICH ARE EVENTUALLY
// FILTERING OUT SOME OF YOUR STORES
}
}
}
}
Pay attention that you have to repeat the eventual nested queries inside the nested filter field. You find then the price in the score field of the response.