A special single bucket aggregation that selects child documents that have the specified type, as defined in a join field.
This aggregation has a single option:
-
type- The child type that should be selected.
For example, let’s say we have an index of questions and answers. The answer type has the following join field in the mapping:
PUT child_example
{
"mappings": {
"properties": {
"join": {
"type": "join",
"relations": {
"question": "answer"
}
}
}
}
}The question document contain a tag field and the answer documents contain an owner field. With the children
aggregation the tag buckets can be mapped to the owner buckets in a single request even though the two fields exist in
two different kinds of documents.
An example of a question document:
PUT child_example/_doc/1
{
"join": {
"name": "question"
},
"body": "<p>I have Windows 2003 server and i bought a new Windows 2008 server...",
"title": "Whats the best way to file transfer my site from server to a newer one?",
"tags": [
"windows-server-2003",
"windows-server-2008",
"file-transfer"
]
}Examples of answer documents:
PUT child_example/_doc/2?routing=1
{
"join": {
"name": "answer",
"parent": "1"
},
"owner": {
"location": "Norfolk, United Kingdom",
"display_name": "Sam",
"id": 48
},
"body": "<p>Unfortunately you're pretty much limited to FTP...",
"creation_date": "2009-05-04T13:45:37.030"
}
PUT child_example/_doc/3?routing=1&refresh
{
"join": {
"name": "answer",
"parent": "1"
},
"owner": {
"location": "Norfolk, United Kingdom",
"display_name": "Troll",
"id": 49
},
"body": "<p>Use Linux...",
"creation_date": "2009-05-05T13:45:37.030"
}The following request can be built that connects the two together:
POST child_example/_search?size=0
{
"aggs": {
"top-tags": {
"terms": {
"field": "tags.keyword",
"size": 10
},
"aggs": {
"to-answers": {
"children": {
"type" : "answer" 
},
"aggs": {
"top-names": {
"terms": {
"field": "owner.display_name.keyword",
"size": 10
}
}
}
}
}
}
}
}
|
The |
The above example returns the top question tags and per tag the top answer owners.
Possible response:
{
"took": 25,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"skipped" : 0,
"failed": 0
},
"hits": {
"total" : {
"value": 3,
"relation": "eq"
},
"max_score": null,
"hits": []
},
"aggregations": {
"top-tags": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "file-transfer",
"doc_count": 1,
"to-answers": {
"doc_count": 2, 
"top-names": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "Sam",
"doc_count": 1
},
{
"key": "Troll",
"doc_count": 1
}
]
}
}
},
{
"key": "windows-server-2003",
"doc_count": 1, 
"to-answers": {
"doc_count": 2, 
"top-names": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "Sam",
"doc_count": 1
},
{
"key": "Troll",
"doc_count": 1
}
]
}
}
},
{
"key": "windows-server-2008",
"doc_count": 1, 
"to-answers": {
"doc_count": 2, 
"top-names": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "Sam",
"doc_count": 1
},
{
"key": "Troll",
"doc_count": 1
}
]
}
}
}
]
}
}
}
|
The number of question documents with the tag |
|
The number of answer documents that are related to question documents with the tag |