56 lines
2.0 KiB
Plaintext
56 lines
2.0 KiB
Plaintext
[[query-dsl-match-query-phrase-prefix]]
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=== Match Phrase Prefix Query
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The `match_phrase_prefix` is the same as `match_phrase`, except that it
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allows for prefix matches on the last term in the text. For example:
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[source,js]
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--------------------------------------------------
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{
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"match_phrase_prefix" : {
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"message" : "quick brown f"
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}
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}
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--------------------------------------------------
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It accepts the same parameters as the phrase type. In addition, it also
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accepts a `max_expansions` parameter (default `50`) that can control to how
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many prefixes the last term will be expanded. It is highly recommended to set
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it to an acceptable value to control the execution time of the query. For
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example:
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[source,js]
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--------------------------------------------------
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{
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"match_phrase_prefix" : {
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"message" : {
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"query" : "quick brown f",
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"max_expansions" : 10
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}
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}
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}
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--------------------------------------------------
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[IMPORTANT]
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===================================================
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The `match_phrase_prefix` query is a poor-man's autocomplete. It is very easy
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to use, which let's you get started quickly with _search-as-you-type_ but it's
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results, which usually are good enough, can sometimes be confusing.
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Consider the query string `quick brown f`. This query works by creating a
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phrase query out of `quick` and `brown` (i.e. the term `quick` must exist and
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must be followed by the term `brown`). Then it looks at the sorted term
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dictionary to find the first 50 terms that begin with `f`, and
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adds these terms to the phrase query.
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The problem is that the first 50 terms may not include the term `fox` so the
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phase `quick brown fox` will not be found. This usually isn't a problem as
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the user will continue to type more letters until the word they are looking
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for appears.
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For better solutions for _search-as-you-type_ see the
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<<search-suggesters-completion,completion suggester>> and
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{guide}/_index_time_search_as_you_type.html[Index-Time Search-as-You-Type].
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=================================================== |