113 lines
5.1 KiB
Plaintext
113 lines
5.1 KiB
Plaintext
[[java-rest-high-explain]]
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=== Explain API
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The explain api computes a score explanation for a query and a specific document.
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This can give useful feedback whether a document matches or didn’t match a specific query.
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[[java-rest-high-explain-request]]
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==== Explain Request
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An `ExplainRequest` expects an `index` and an `id` to specify a certain document,
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and a query represented by `QueryBuilder` to run against it (the way of <<java-rest-high-query-builders, building queries>>).
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-request]
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--------------------------------------------------
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===== Optional arguments
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-request-routing]
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--------------------------------------------------
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<1> Set a routing parameter
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-request-preference]
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--------------------------------------------------
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<1> Use the preference parameter e.g. to execute the search to prefer local
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shards. The default is to randomize across shards.
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-request-source]
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--------------------------------------------------
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<1> Set to true to retrieve the _source of the document explained. You can also
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retrieve part of the document by using _source_include & _source_exclude
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(see <<java-rest-high-document-get-request-optional-arguments, Get API>> for more details)
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-request-stored-field]
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--------------------------------------------------
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<1> Allows to control which stored fields to return as part of the document explained
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(requires the field to be stored separately in the mappings).
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[[java-rest-high-explain-sync]]
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==== Synchronous Execution
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The `explain` method executes the request synchronously:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-execute]
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--------------------------------------------------
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[[java-rest-high-explain-async]]
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==== Asynchronous Execution
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The `explainAsync` method executes the request asynchronously,
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calling the provided `ActionListener` when the response is ready:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-execute-async]
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--------------------------------------------------
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<1> The `ExplainRequest` to execute and the `ActionListener` to use when
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the execution completes.
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The asynchronous method does not block and returns immediately. Once the request
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completes, the `ActionListener` is called back using the `onResponse` method
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if the execution successfully completed or using the `onFailure` method if
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it failed.
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A typical listener for `ExplainResponse` is constructed as follows:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-execute-listener]
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--------------------------------------------------
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<1> Called when the execution is successfully completed.
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<2> Called when the whole `ExplainRequest` fails.
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[[java-rest-high-explain-response]]
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==== ExplainResponse
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The `ExplainResponse` contains the following information:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[explain-response]
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--------------------------------------------------
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<1> The index name of the explained document.
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<2> The id of the explained document.
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<3> Indicates whether or not the explained document exists.
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<4> Indicates whether or not there is a match between the explained document and
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the provided query (the `match` is retrieved from the lucene `Explanation` behind the scenes
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if the lucene `Explanation` models a match, it returns `true`, otherwise it returns `false`).
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<5> Indicates whether or not there exists a lucene `Explanation` for this request.
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<6> Get the lucene `Explanation` object if there exists.
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<7> Get the `GetResult` object if the `_source` or the stored fields are retrieved.
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The `GetResult` contains two maps internally to store the fetched `_source` and stored fields.
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You can use the following methods to get them:
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["source","java",subs="attributes,callouts,macros"]
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--------------------------------------------------
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include-tagged::{doc-tests}/SearchDocumentationIT.java[get-result]
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--------------------------------------------------
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<1> Retrieve the `_source` as a map.
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<2> Retrieve the specified stored fields as a map.
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