$text¶
- $text¶
2.6 新版功能.
$text performs a text search on the content of the fields indexed with a text index. A $text expression has the following syntax:
{ $text: { $search: <string>, $language: <string> } }
The $text operator accepts a text query document with the following fields:
Field Type Description $search string A string of terms that MongoDB parses and uses to query the text index. MongoDB performs a logical OR search of the terms unless specified as a phrase. See Behavior for more information on the field. $language string Optional. The language that determines the list of stop words for the search and the rules for the stemmer and tokenizer. If not specified, the search uses the default language of the index. For supported languages, see 文本搜索语言.
If you specify a language value of "none", then the text search uses simple tokenization with no list of stop words and no stemming.
The $text operator, by default, does not return results sorted in terms of the results’ score. For more information, see the Text Score documentation.
Behavior¶
Restrictions¶
- A query can specify, at most, one $text expression.
- The $text query can not appear in $nor expressions.
- To use a $text query in an $or expression, all clauses in the $or array must be indexed.
- You cannot use hint() if the query includes a $text query expression.
- You cannot specify $natural sort order if the query includes a $text expression.
- You cannot combine the $text expression, which requires a special text index, with a query operator that requires a different type of special index. For example you cannot combine $text expression with the $near operator.
$search Field¶
In the $search field, specify a string of words that the text operator parses and uses to query the text index. The text operator treats most punctuation in the string as delimiters, except a hyphen - that negates term or an escaped double quotes \" that specifies a phrase.
Phrases¶
To match on a phrase, as opposed to individual terms, enclose the phrase in escaped double quotes (\"), as in:
"\"ssl certificate\""
If the $search string includes a phrase and individual terms, text search will only match the documents that include the phrase. More specifically, the search performs a logical AND of the phrase with the individual terms in the search string.
For example, passed a $search string:
"\"ssl certificate\" authority key"
The $text operator searches for the phrase "ssl certificate" and ("authority" or "key" or "ssl" or "certificate" ).
Negations¶
Prefixing a word with a hyphen sign (-) negates a word:
- The negated word excludes documents that contain the negated word from the result set.
- When passed a search string that only contains negated words, text search will not match any documents.
- A hyphenated word, such as pre-market, is not a negation. The $text operator treats the hyphen as a delimiter.
The $text operator adds all negations to the query with the logical AND operator.
Match Operation¶
The $text operator ignores language-specific stop words, such as the and and in English.
The $text operator matches on the complete stemmed word. So if a document field contains the word blueberry, a search on the term blue will not match. However, blueberry or blueberries will match.
For non-diacritics, text search is case insensitive; i.e. case insensitive for [A-z].
Text Score¶
The $text operator assigns a score to each document that contains the search term in the indexed fields. The score represents the relevance of a document to a given text search query. The score can be part of a sort() method specification as well as part of the projection expression. The { $meta: "textScore" } expression provides information on the processing of the $text operation. See $meta projection operator for details on accessing the score for projection or sort.
Examples¶
The following examples assume a collection articles that has a text index on the field subject:
db.articles.ensureIndex( { subject: "text" } )
Search for a Single Word¶
The following query searches for the term coffee:
db.articles.find( { $text: { $search: "coffee" } } )
This query returns documents that contain the term coffee in the indexed subject field.
Match Any of the Search Terms¶
If the search string is a space-delimited string, $text operator performs a logical OR search on each term and returns documents that contains any of the terms.
The following query searches specifies a $search string of three terms delimited by space, "bake coffee cake":
db.articles.find( { $text: { $search: "bake coffee cake" } } )
This query returns documents that contain either bake or coffee or cake in the indexed subject field.
Search for a Phrase¶
To match the exact phrase as a single term, escape the quotes.
The following query searches for the phrase coffee cake:
db.articles.find( { $text: { $search: "\"coffee cake\"" } } )
This query returns documents that contain the phrase coffee cake.
参见
Exclude Documents That Contain a Term¶
A negated term is a term that is prefixed by a minus sign -. If you negate a term, the $text operator will exclude the documents that contain those terms from the results.
The following example searches for documents that contain the words bake or coffee but do not contain the term cake:
db.articles.find( { $text: { $search: "bake coffee -cake" } } )
参见
Return the Text Search Score¶
The following query searches for the term cake and returns the score assigned to each matching document:
db.articles.find(
{ $text: { $search: "cake" } },
{ score: { $meta: "textScore" } }
)
In the result set, the returned documents includes an additional field score that contains the document’s score associated with the text search. [1]
参见
Sort by Text Search Score¶
To sort by the text score, include the same $meta expression in both the projection document and the sort expression. [1] The following query searches for the term cake and sorts the results by the descending score:
db.articles.find(
{ $text: { $search: "cake" } },
{ score: { $meta: "textScore" } }
).sort( { score: { $meta: "textScore" } } )
In the result set, the returned documents includes an additional field score that contains the document’s score associated with the text search.
参见
Return Top 3 Matching Documents¶
Use the limit() method in conjunction with a sort() to return the top three matching documents. The following query searches for the term cake and sorts the results by the descending score:
db.articles.find(
{ $text: { $search: "cake" } },
{ score: { $meta: "textScore" } }
).sort( { score: { $meta: "textScore" } } ).limit(3)
参见
Text Search with Additional Query and Sort Expressions¶
The following query searches for documents with status equal to "A" that contain the terms coffee or cake in the indexed field subject and specifies a sort order of ascending date, descending text score:
db.articles.find(
{ status: "A", $text: { $search: "coffee cake" } },
{ score: { $meta: "textScore" } }
).sort( { date: 1, score: { $meta: "textScore" } } )
Search a Different Language¶
Use the optional $language field in the $text expression to specify a language that determines the list of stop words and the rules for the stemmer and tokenizer for the search string.
If you specify a language value of "none", then the text search uses simple tokenization with no list of stop words and no stemming.
The following query specifies es for Spanish as the language that determines the tokenization, stemming, and stop words:
db.articles.find(
{ $text: { $search: "leche", $language: "es" } }
)
The $text expression can also accept the language by name, spanish. See 文本搜索语言 for the supported languages.
参见
| [1] | (1, 2) The behavior and requirements of the $meta operator differs from that of the $meta aggregation operator. See the $meta aggregation operator for details. |