76 lines
2.0 KiB
Plaintext
76 lines
2.0 KiB
Plaintext
[[mapping-index-field]]
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=== `_index` field
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When performing queries across multiple indexes, it is sometimes desirable to
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add query clauses that are associated with documents of only certain indexes.
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The `_index` field allows matching on the index a document was indexed into.
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Its value is accessible in certain queries and aggregations, and when sorting
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or scripting:
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[source,console]
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--------------------------
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PUT index_1/_doc/1
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{
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"text": "Document in index 1"
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}
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PUT index_2/_doc/2?refresh=true
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{
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"text": "Document in index 2"
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}
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GET index_1,index_2/_search
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{
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"query": {
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"terms": {
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"_index": ["index_1", "index_2"] <1>
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}
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},
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"aggs": {
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"indices": {
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"terms": {
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"field": "_index", <2>
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"size": 10
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}
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}
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},
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"sort": [
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{
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"_index": { <3>
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"order": "asc"
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}
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}
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],
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"script_fields": {
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"index_name": {
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"script": {
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"lang": "painless",
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"source": "doc['_index']" <4>
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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> Querying on the `_index` field
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<2> Aggregating on the `_index` field
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<3> Sorting on the `_index` field
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<4> Accessing the `_index` field in scripts
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The `_index` field is exposed virtually -- it is not added to the Lucene index
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as a real field. This means that you can use the `_index` field in a `term` or
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`terms` query (or any query that is rewritten to a `term` query, such as the
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`match`, `query_string` or `simple_query_string` query), as well as `prefix`
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and `wildcard` queries. However, it does not support `regexp` and `fuzzy`
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queries.
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Queries on the `_index` field accept index aliases in addition to concrete
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index names.
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NOTE: When specifying a remote index name such as `cluster_1:index_3`, the
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query must contain the separator character `:`. For example, a `wildcard` query
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on `cluster_*:index_3` would match documents from the remote index. However, a
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query on `cluster*index_1` is only matched against local indices, since no
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separator is present. This behavior aligns with the usual resolution rules for
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remote index names.
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