119 lines
3.6 KiB
Plaintext
119 lines
3.6 KiB
Plaintext
[[search-aggregations-bucket-reverse-nested-aggregation]]
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=== Reverse nested Aggregation
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A special single bucket aggregation that enables aggregating on parent docs from nested documents. Effectively this
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aggregation can break out of the nested block structure and link to other nested structures or the root document,
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which allows nesting other aggregations that aren't part of the nested object in a nested aggregation.
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The `reverse_nested` aggregation must be defined inside a `nested` aggregation.
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.Options:
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* `path` - Which defines to what nested object field should be joined back. The default is empty,
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which means that it joins back to the root / main document level. The path cannot contain a reference to
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a nested object field that falls outside the `nested` aggregation's nested structure a `reverse_nested` is in.
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For example, lets say we have an index for a ticket system with issues and comments. The comments are inlined into
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the issue documents as nested documents. The mapping could look like:
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[source,js]
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--------------------------------------------------
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{
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...
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"issue" : {
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"properties" : {
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"tags" : { "type" : "string" }
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"comments" : { <1>
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"type" : "nested"
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"properties" : {
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"username" : { "type" : "string", "index" : "not_analyzed" },
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"comment" : { "type" : "string" }
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}
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}
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}
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}
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}
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--------------------------------------------------
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<1> The `comments` is an array that holds nested documents under the `issue` object.
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The following aggregations will return the top commenters' username that have commented and per top commenter the top
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tags of the issues the user has commented on:
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[source,js]
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--------------------------------------------------
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{
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"query": {
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"match": {
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"name": "led tv"
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}
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},
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"aggs": {
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"comments": {
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"nested": {
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"path": "comments"
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},
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"aggs": {
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"top_usernames": {
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"terms": {
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"field": "comments.username"
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},
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"aggs": {
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"comment_to_issue": {
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"reverse_nested": {}, <1>
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"aggs": {
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"top_tags_per_comment": {
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"terms": {
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"field": "tags"
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}
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}
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}
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}
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}
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}
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}
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}
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}
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}
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--------------------------------------------------
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As you can see above, the the `reverse_nested` aggregation is put in to a `nested` aggregation as this is the only place
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in the dsl where the `reversed_nested` aggregation can be used. Its sole purpose is to join back to a parent doc higher
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up in the nested structure.
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<1> A `reverse_nested` aggregation that joins back to the root / main document level, because no `path` has been defined.
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Via the `path` option the `reverse_nested` aggregation can join back to a different level, if multiple layered nested
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object types have been defined in the mapping
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Possible response snippet:
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[source,js]
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--------------------------------------------------
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{
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"aggregations": {
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"comments": {
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"top_usernames": {
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"buckets": [
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{
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"key": "username_1",
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"doc_count": 12,
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"comment_to_issue": {
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"top_tags_per_comment": {
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"buckets": [
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{
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"key": "tag1",
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"doc_count": 9
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},
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...
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]
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}
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}
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},
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...
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]
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}
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}
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}
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}
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--------------------------------------------------
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