Text Indexes文本索引¶

Overview概述¶

MongoDB provides text indexes to support text search queries on string content. MongoDB提供文本索引以支持对字符串内容的文本搜索查询。text indexes can include any field whose value is a string or an array of string elements.text索引可以包括值为字符串或字符串元素数组的任何字段。

Versions¶

To override the default version and specify a different version, include the option { "textIndexVersion": <version> } when creating the index.要覆盖默认版本并指定其他版本，请在创建索引时包含选项{ "textIndexVersion": <version> }。

Create Text Index创建文本索引¶

To create a text index, use the db.collection.createIndex() method. 要创建text索引，请使用db.collection.createIndex()方法。To index a field that contains a string or an array of string elements, include the field and specify the string literal "text" in the index document, as in the following example:要为包含字符串或字符串元素数组的字段编制索引，请在索引文档中包含该字段并指定字符串文字"text"，如下例所示：

db.reviews.createIndex( { comments: "text" } )

You can index multiple fields for the text index. 可以为text索引的多个字段编制索引。The following example creates a text index on the fields subject and comments:以下示例创建了subject和commands字段的text索引：

db.reviews.createIndex(
   {
     subject: "text",
     comments: "text"
   }
 )

A compound index can include text index keys in combination with ascending/descending index keys. 复合索引可以包括text索引键和升序/降序索引键。For more information, see Compound Index.有关更多信息，请参阅复合索引。

In order to drop a text index, use the index name. 要删除text索引，请使用索引名称。See Use the Index Name to Drop a text Index for more information.有关更多信息，请参阅使用索引名删除文本索引。

db.collection.createIndex( { "$**": "text" } )

db.collection.createIndex( { a: 1, "$**": "text" } )

Case Insensitivity大小写不敏感¶

The version 3 text index supports the common C, simple S, and for Turkish languages, the special T case foldings as specified in Unicode 8.0 Character Database Case Folding.

The case foldings expands the case insensitivity of the text index to include characters with diacritics, such as é and É, and characters from non-Latin alphabets, such as “И” and “и” in the Cyrillic alphabet.

Version 3 of the text index is also diacritic insensitive. As such, the index also does not distinguish between é, É, e, and E.

Previous versions of the text index are case insensitive for [A-z] only; i.e. case insensitive for non-diacritics Latin characters only . For all other characters, earlier versions of the text index treat them as distinct.对于所有其他字符，早期版本的文本索引将它们视为不同的字符。

Diacritic Insensitivity变音不敏感¶

With version 3, text index is diacritic insensitive. 对于版本3，text索引不区分重音。That is, the index does not distinguish between characters that contain diacritical marks and their non-marked counterpart, such as é, ê, and e. More specifically, the text index strips the characters categorized as diacritics in Unicode 8.0 Character Database Prop List.

Version 3 of the text index is also case insensitive to characters with diacritics. As such, the index also does not distinguish between é, É, e, and E.

Previous versions of the text index treat characters with diacritics as distinct.以前版本的text索引将带变音符号的字符视为不同的字符。

Tokenization Delimiters标记化分隔符¶

For tokenization, version 3 text index uses the delimiters categorized under Dash, Hyphen, Pattern_Syntax, Quotation_Mark, Terminal_Punctuation, and White_Space in Unicode 8.0 Character Database Prop List.

For example, if given a string "Il a dit qu'il «était le meilleur joueur du monde»", the text index treats «, », and spaces as delimiters.

Previous versions of the index treat « as part of the term "«était" and » as part of the term "monde»".

Index Entries索引项¶

text index tokenizes and stems the terms in the indexed fields for the index entries. text index stores one index entry for each unique stemmed term in each indexed field for each document in the collection. The index uses simple language-specific suffix stemming.

Supported Languages and Stop Words支持的语言和停止词¶

MongoDB supports text search for various languages. MongoDB支持各种语言的文本搜索。text indexes drop language-specific stop words (e.g. in English, the, an, a, and, etc.) and use simple language-specific suffix stemming. For a list of the supported languages, see Text Search Languages.

If you specify a language value of "none", then the text index uses simple tokenization with no list of stop words and no stemming.

To specify a language for the text index, see Specify a Language for Text Index.

sparse Property属性¶

text indexes are always sparse and ignore the sparse option. text索引总是稀疏的，忽略sparse选项。If a document lacks a text index field (or the field is null or an empty array), MongoDB does not add an entry for the document to the text index. 如果文档缺少text索引字段（或字段为null或空数组），MongoDB不会将文档条目添加到文本索引中。For inserts, MongoDB inserts the document but does not add to the text index.对于插入，MongoDB会插入文档，但不会添加到text索引中。

For a compound index that includes a text index key along with keys of other types, only the text index field determines whether the index references a document. 对于包含text索引键和其他类型键的复合索引，只有text索引字段确定索引是否引用文档。The other keys do not determine whether the index references the documents or not.其他键不确定索引是否引用文档。

Restrictions限制¶

Storage Requirements and Performance Costs存储要求和性能成本¶

text indexes have the following storage requirements and performance costs:text索引具有以下存储要求和性能成本：

• text indexes can be large. text索引可以很大。They contain one index entry for each unique post-stemmed word in each indexed field for each document inserted.对于插入的每个文档，它们在每个索引字段中为每个唯一的词干词包含一个索引项。
• Building a text index is very similar to building a large multi-key index and will take longer than building a simple ordered (scalar) index on the same data.
• When building a large text index on an existing collection, ensure that you have a sufficiently high limit on open file descriptors. See the recommended settings.
• text indexes will impact insertion throughput because MongoDB must add an index entry for each unique post-stemmed word in each indexed field of each new source document.
• Additionally, text indexes do not store phrases or information about the proximity of words in the documents. As a result, phrase queries will run much more effectively when the entire collection fits in RAM.

Text Search Support文本搜索支持¶

The text index supports $text query operations. For examples of text search, see the $text reference page. For examples of $text operations in aggregation pipelines, see Text Search in the Aggregation Pipeline.