Collation排序规则¶

Local Variants局部变异¶

Some collation locales have variants, which employ special language-specific rules. 一些排序规则区域设置有变体，它们使用特定于语言的特殊规则。To specify a locale variant, use the following syntax:要指定区域设置变量，请使用以下语法：

{ "locale" : "<locale code>@collation=<variant>" }

For example, to use the unihan variant of the Chinese collation:例如，要使用中文排序规则的unihan变体：

{ "locale" : "zh@collation=unihan" }

For a complete list of all collation locales and their variants, see Collation Locales.有关所有排序规则区域设置及其变体的完整列表，请参阅排序规则区域设置。

Collation and Views排序规则和视图¶

• You can specify a default collation for a view at creation time. 可以在创建时为视图指定默认排序规则。If no collation is specified, the view’s default collation is the “simple” binary comparison collator. 如果未指定排序规则，则视图的默认排序规则是“简单”二进制比较排序器。That is, the view does not inherit the collection’s default collation.也就是说，视图不会继承集合的默认排序规则。
• String comparisons on the view use the view’s default collation. 视图上的字符串比较使用视图的默认排序规则。An operation that attempts to change or override a view’s default collation will fail with an error.尝试更改或覆盖视图默认排序规则的操作将失败并出现错误。
• If creating a view from another view, you cannot specify a collation that differs from the source view’s collation.如果从另一个视图创建视图，则不能指定与源视图排序规则不同的排序规则。
• If performing an aggregation that involves multiple views, such as with $lookup or $graphLookup, the views must have the same collation.如果执行涉及多个视图的聚合，例如使用$lookup或$graphLookup，则这些视图必须具有相同的排序规则。

Collation and Index Use排序和索引使用¶

To use an index for string comparisons, an operation must also specify the same collation. 要使用索引进行字符串比较，操作还必须指定相同的排序规则。That is, an index with a collation cannot support an operation that performs string comparisons on the indexed fields if the operation specifies a different collation.也就是说，如果操作指定了不同的排序规则，则具有排序规则的索引不能支持对索引字段执行字符串比较的操作。

For example, the collection myColl has an index on a string field category with the collation locale "fr".例如，集合myColl在排序规则区域设置为 "fr"的字符串字段category上有一个索引。

db.myColl.createIndex( { category: 1 }, { collation: { locale: "fr" } } )

The following query operation, which specifies the same collation as the index, can use the index:以下查询操作指定了与索引相同的排序规则，可以使用索引：

db.myColl.find( { category: "cafe" } ).collation( { locale: "fr" } )

However, the following query operation, which by default uses the “simple” binary collator, cannot use the index:但是，以下查询操作（默认情况下使用“简单”二进制排序器）不能使用索引：

db.myColl.find( { category: "cafe" } )

For a compound index where the index prefix keys are not strings, arrays, and embedded documents, an operation that specifies a different collation can still use the index to support comparisons on the index prefix keys.对于索引前缀键不是字符串、数组和嵌入文档的复合索引，指定不同排序规则的操作仍然可以使用索引来支持索引前缀键的比较。

For example, the collection myColl has a compound index on the numeric fields score and price and the string field category; the index is created with the collation locale "fr" for string comparisons:例如，集合myColl在数字字段score和price以及字符串字段category上有一个复合索引；索引是使用排序规则区域设置"fr"创建的，用于字符串比较：

db.myColl.createIndex(
   { score: 1, price: 1, category: 1 },
   { collation: { locale: "fr" } } )

The following operations, which use "simple" binary collation for string comparisons, can use the index:以下使用"simple"二进制排序规则进行字符串比较的操作可以使用索引：

db.myColl.find( { score: 5 } ).sort( { price: 1 } )
db.myColl.find( { score: 5, price: { $gt: NumberDecimal( "10" ) } } ).sort( { price: 1 } )

The following operation, which uses "simple" binary collation for string comparisons on the indexed category field, can use the index to fulfill only the score: 5 portion of the query:以下操作使用"simple"二进制排序规则对索引category字段进行字符串比较，可以使用索引只完成查询的score: 5部分：

db.myColl.find( { score: 5, category: "cafe" } )