ElasticSearch source filtering array of objects - elasticsearch

Question

Here is a document
{
"Id": "1",
"Name": "Thing",
"Prices": [
{"CompanyId": "1", "Price": "11.11"},
{"CompanyId": "2", "Price": "12.12"},
{"CompanyId": "3", "Price": "13.13"}
And here is the associated ElasticSearch schema:
"Prices" : {
"type" : "nested",
"properties" : {
"CompanyId": {
"type" : "integer"
},
"Price" : {
"type" : "scaled_float",
"scaling_factor" : 100
}
}
}
If a user is buying for CompantId = 3 then the supplier doesn't want them to be able to see the preferential pricing for CompanyId = 1, say.
Therefore I need to use a source filter to remove all prices for which the CompanyId is not 3.
I have found that this works.
"_source":{
"excludes": ["Prices.companyId.CompanyId"]
}
But I don't understand how or why.
It can't possibly work because the required CompanyId is not mentioned anywhere in the whole ElasticSearch search JSON.
Adding a full search JSON:
{
"query":{
"bool":{
"must":[
{
"match_all":{
}
}
],
"filter":{
"match":{
"PurchasingViews":6060
}
}
}
},
"size":20,
"aggs":{
"CompanyName.raw":{
"terms":{
"field":"CompanyName.raw",
"size":20,
"order":{
"_count":"desc"
}
}
}
},
"_source":{
"excludes":[
"PurchasingViews",
"ContractFilters",
"SearchField*",
"Keywords*",
"Menus*",
"Prices.companyId.CompanyId"
]
}
}
Result:
{
"took":224,
"timed_out":false,
"_shards":{
"total":5,
"successful":5,
"skipped":0,
"failed":0
},
"hits":{
"total":1173525,
"max_score":1.0,
"hits":[
{
"_index":"products_purchasing",
"_type":"product_purchasing",
"_id":"12787114",
"_score":1.0,
"_source":{
"CompanyName":"...",
"Prices":[
{
"CompanyId":1474,
"Price":697.3
}
],
"CompanyId":571057,
"PartNumber":"...",
"LongDescription_en":"...",
"Name_en":"...",
"DescriptionSnippet_en":"...",
"ProductId":9605985,
"Id":12787114
}
}
]
},
"aggregations":{
"CompanyName.raw":{
"doc_count_error_upper_bound":84,
"sum_other_doc_count":21078,
"buckets":[
{
"key":"...",
"doc_count":534039
}
]
}
}
}

Answer 1

https://www.elastic.co/guide/en/elasticsearch/reference/current/nested.html
I believe the way you have put your mapping with the "nested" type has created the reference you are questioning.
Also - I would suggest framing the query as looking for 3 only rather than "excluding" everything except 3