OpenSearch/docs/java-rest/high-level/apis/search.asciidoc

[[java-rest-high-search]]
=== Search API

[[java-rest-high-document-search-request]]
==== Search Request

The `SearchRequest` is used for any operation that has to do with searching
documents, aggregations, suggestions and also offers ways of requesting
highlighting on the resulting documents.

In its most basic form, we can add a query to the request:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-basic]
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<1> Creates the `SeachRequest`. Without arguments this runs against all indices.
<2> Most search parameters are added to the `SearchSourceBuilder`. It offers setters for everything that goes into the search request body.
<3> Add a `match_all` query to the `SearchSourceBuilder`.

===== Optional arguments

Let's first look at some of the optional arguments of a `SearchRequest`:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-indices-types]
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<1> Restricts the request to an index
<2> Limits the request to a type

There are a couple of other interesting optional parameters:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-routing]
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<1> Set a routing parameter

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-indicesOptions]
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<1> Setting `IndicesOptions` controls how unavailable indices are resolved and
how wildcard expressions are expanded

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-preference]
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<1> Use the preference parameter e.g. to execute the search to prefer local
shards. The default is to randomize across shards.

===== Using the SearchSourceBuilder

Most options controlling the search behavior can be set on the
`SearchSourceBuilder`,
which contains more or less the equivalent of the options in the search request
body of the Rest API.

Here are a few examples of some common options:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-basics]
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<1> Create a `SearchSourceBuilder` with default options.
<2> Set the query. Can be any type of `QueryBuilder`
<3> Set the `from` option that determines the result index to start searching
from. Defaults to 0.
<4> Set the `size` option that determines the number of search hits to return.
Defaults to 10.
<5> Set an optional timeout that controls how long the search is allowed to
take.

After this, the `SearchSourceBuilder` only needs to be added to the
`SearchRequest`:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-source-setter]
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===== Requesting Aggregations

Aggregations can be added to the search by first creating the appropriate
`AggregationBuilder` and then setting it on the `SearchSourceBuilder`. In the
following example we create a `terms` aggregation on company names with a
sub-aggregation on the average age of employees in the company:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations]
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We will later see how to <<java-rest-high-retrieve-aggs,access aggregations>> in the `SearchResponse`.

===== Requesting Suggestions

To add Suggestions to the search request, use one of the `SuggestionBuilder` implementations
that are easily accessible from the `SuggestBuilders` factory class. Suggestion builders
need to be added to the top level `SuggestBuilder`, which itself can be set on the  `SearchSourceBuilder`.

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-suggestion]
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<1> Creates a new `TermSuggestionBuilder` for the `user` field and
the text `kmichy`
<2> Adds the suggestion builder and names it `suggest_user`

We will later see how to <<java-rest-high-retrieve-suggestions,retrieve suggestions>> from the 
`SearchResponse`.

[[java-rest-high-document-search-sync]]
==== Synchronous Execution

When executing a `SearchRequest` in the following manner, the client waits
for the `SearchResponse` to be returned before continuing with code execution:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-execute]
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[[java-rest-high-document-search-async]]
==== Asynchronous Execution


Executing a `SearchRequest` can also be done in an asynchronous fashion so that
the client can return directly. Users need to specify how the response or
potential failures will be handled by passing in appropriate listeners:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-execute-async]
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<1> Called when the execution is successfully completed.
<2> Called when the whole `SearchRequest` fails.

==== SearchResponse

The `SearchResponse` that is returned by executing the search provides details
about the search execution itself as well as access to the documents returned.
First, there is useful information about the request execution itself, like the
HTTP status code, execution time or wether the request terminated early or timed
out:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-response-1]
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Second, the response also provides information about the execution on the
shard level by offering statistics about the total number of shards that were
affected by the search, and the successful vs. unsuccessful shards. Possible
failures can also be handled by iterating over an array off
`ShardSearchFailures` like in the following example:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-response-2]
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[[java-rest-high-retrieve-searchHits]]
===== Retrieving SearchHits

To get access to the returned documents, we need to first get the `SearchHits`
contained in the response:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-get]
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The `SearchHits` provides global information about all hits, like total number
of hits or the maximum score:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-info]
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Nested inside the `SearchHits` are the individual search results that can
be iterated over:


["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-singleHit]
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The `SearchHit` provides access to basic information like index, type, docId and
score of each search hit:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-singleHit-properties]
--------------------------------------------------

Furthermore, it lets you get back the document source, either as a simple
JSON-String or as a map of key/value pairs. In this map, regular fields
are keyed by the field name and contain the field value. Multi-valued fields are
returned as lists of objects, nested objects as another key/value map. These
cases need to be cast accordingly:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-hits-singleHit-source]
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[[java-rest-high-retrieve-aggs]]
===== Retrieving Aggregations

Aggregations can be retrieved from the `SearchResponse` by first getting the
root of the aggregation tree, the `Aggregations` object, and then getting the
aggregation by name.

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-get]
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<1> Get the `by_company` terms aggregation
<2> Get the buckets that is keyed with `Elastic`
<3> Get the `average_age` sub-aggregation from that bucket

Note that if you access aggregations by name, you need to specify the
aggregation interface according to the type of aggregation you requested,
otherwise a `ClassCastException` will be thrown:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-get-wrongCast]
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<1> This will throw an exception because "by_company" is a `terms` aggregation
but we try to retrieve it as a `range` aggregation

It is also possible to access all aggregations as a map that is keyed by the
aggregation name. In this case, the cast to the proper aggregation interface
needs to happen explicitly:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-asMap]
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There are also getters that return all top level aggregations as a list:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-asList]
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And last but not least you can iterate over all aggregations and then e.g.
decide how to further process them based on their type:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-aggregations-iterator]
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[[java-rest-high-retrieve-suggestions]]
===== Retrieving Suggestions

To get back the suggestions from a `SearchResponse`, use the `Suggest` object as an entry point and then retrieve the nested suggestion objects:

["source","java",subs="attributes,callouts,macros"]
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include-tagged::{doc-tests}/SearchDocumentationIT.java[search-request-suggestion-get]
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<1> Use the `Suggest` class to access suggestions
<2> Suggestions can be retrieved by name. You need to assign them to the correct
type of Suggestion class (here `TermSuggestion`), otherwise a `ClassCastException` is thrown
<3> Iterate over the suggestion entries
<4> Iterate over the options in one entry