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$regexFindAll (aggregation)

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Definition定义

$regexFindAll

New in version 4.2. 4.2版新增。

Provides regular expression (regex) pattern matching capability in aggregation expressions. The operator returns an array of documents that contains information on each match. If a match is not found, returns an empty array.在聚合表达式中提供正则表达式（regex）模式匹配功能。运算符返回一个文档数组，其中包含每个匹配项的信息。如果未找到匹配项，则返回一个空数组。

Prior to MongoDB 4.2, aggregation pipeline can only use the query operator $regex in the $match stage. 在MongoDB 4.2之前，聚合管道只能在$match阶段使用查询运算符$regex。For more information on using regex in a query, see $regex.有关在查询中使用regex的更多信息，请参阅$regex。

Syntax语法

The $regexFindAll operator has the following syntax:$regexFindAll运算符具有以下语法：

{ $regexFindAll: { input: <expression> , regex: <expression>, options: <expression> } }
Field字段Description描述
inputThe string on which you wish to apply the regex pattern. Can be a string or any valid expression that resolves to a string. 要应用正则表达式模式的字符串。可以是字符串，也可以是解析为字符串的任何有效表达式。
regexThe regex pattern to apply. 要应用的正则表达式模式。Can be any valid expression that resolves to either a string or regex pattern /<pattern>/. 可以是解析为字符串或正则表达式模式/<pattern>/的任何有效表达式。When using the regex /<pattern>/, you can also specify the regex options i and m (but not the s or x options): 使用正则表达式/<pattern>/时，还可以指定regex选项i和m（但不能指定s或x选项）：
  • "pattern"
  • /<pattern>/
  • /<pattern>/<options>
Alternatively, you can also specify the regex options with the options field. 或者，您也可以使用options字段指定regex选项。To specify the s or x options, you must use the options field.若要指定s或x选项，必须使用options字段。
You cannot specify options in both the regex and the options field. 不能在regex和options字段中都指定选项。
optionsOptional. 可选。The following <options> are available for use with regular expression. 以下<options>可用于正则表达式。
Note
You cannot specify options in both the regex and the options field. 不能在regex和options字段中都指定选项。
Option选项Description描述
iCase insensitivity to match both upper and lower cases. 区分大小写以匹配大小写。You can specify the option in the options field or as part of the regex field.您可以在options字段中指定该选项，也可以将其作为正则表达式字段的一部分。
mFor patterns that include anchors (i.e. ^ for the start, $ for the end), match at the beginning or end of each line for strings with multiline values. 对于包含锚点的模式（例如，^表示开始，$表示结束），对于具有多行值的字符串，请在每行的开头或末尾进行匹配。Without this option, these anchors match at beginning or end of the string.如果没有此选项，这些锚点将在字符串的开头或末尾匹配。
If the pattern contains no anchors or if the string value has no newline characters (e.g. \n), the m option has no effect. 如果模式不包含锚，或者字符串值没有换行符（例如\n），则m选项无效。
x"Extended" capability to ignore all white space characters in the pattern unless escaped or included in a character class.“扩展”功能可以忽略模式中的所有空白字符，除非转义或包含在字符类中。
Additionally, it ignores characters in-between and including an un-escaped hash/pound (#) character and the next new line, so that you may include comments in complicated patterns. 此外，它会忽略介于之间的字符，并包括一个未转义的hash/pund（#）字符和下一个新行，这样您就可以以复杂的模式包含注释。This only applies to data characters; white space characters may never appear within special character sequences in a pattern.这仅适用于数据字符；空白字符可能永远不会出现在模式中的特殊字符序列中。
The x option does not affect the handling of the VT character (i.e. code 11).x选项不影响VT字符（即代码11）的处理。
You can specify the option only in the options field. 只能在options字段中指定选项。
sAllows the dot character (i.e. .) to match all characters including newline characters.允许点字符（即.）与包括换行符在内的所有字符匹配。
You can specify the option only in the options field. 只能在options字段中指定选项。

Returns返回

The operator returns an array:运算符返回一个数组：

  • If the operator does not find a match, the operator returns an empty array.如果运算符找不到匹配项，则运算符将返回一个空数组。
  • If the operator finds a match, the operator returns an array of documents that contains the following information for each match:如果运算符找到匹配项，则运算符会返回一组文档，其中包含每个匹配项的以下信息：

    • the matching string in the input,input中的匹配字符串，
    • the code point index (not byte index) of the matching string in the input, and输入中匹配字符串的代码点索引（而非字节索引），以及
    • An array of the strings that corresponds to the groups captured by the matching string. 与匹配字符串捕获的组相对应的字符串数组。Capturing groups are specified with unescaped parenthesis () in the regex pattern.捕获组是用regex模式中未加括号()指定的。
    [ { "match" : <string>, "idx" : <num>, "captures" : <array of strings> }, ... ]
Tip

See also: 另请参阅：

Behavior行为

PCRE Library

Starting in version 6.1, MongoDB uses the PCRE2 (Perl Compatible Regular Expressions) library to implement regular expression pattern matching. 从6.1版本开始，MongoDB使用PCRE2(PerlCompatibleRegularExpressions)库来实现正则表达式模式匹配。To learn more about PCRE2, see the PCRE Documentation.要了解有关PCRE2的更多信息，请参阅PCRE文档。

$regexFindAll and Collation和排序规则

$regexFindAll ignores the collation specified for the collection, db.collection.aggregate(), and the index, if used.忽略为集合指定的排序规则db.collection.aggregate()和索引（如果使用）。

For example, the create a sample collection with collation strength 1 (i.e. compare base character only and ignore other differences such as case and diacritics):例如，创建排序规则强度为1的示例集合（即，仅比较基本字符，忽略其他差异，如大小写和变音符号）：

db.createCollection( "myColl", { collation: { locale: "fr", strength: 1 } } )

Insert the following documents:插入以下文件：

db.myColl.insertMany([
   { _id: 1, category: "café" },
   { _id: 2, category: "cafe" },
   { _id: 3, category: "cafE" }
])

Using the collection's collation, the following operation performs a case-insensitive and diacritic-insensitive match:使用集合的排序规则，以下操作执行不区分大小写和不区分重音符号的匹配：

db.myColl.aggregate( [ { $match: { category: "cafe" } } ] )

The operation returns the following 3 documents:该操作返回以下3个文档：

{ "_id" : 1, "category" : "café" }
{ "_id" : 2, "category" : "cafe" }
{ "_id" : 3, "category" : "cafE" }

However, the aggregation expression $regexFind ignores collation; that is, the following regular expression pattern matching examples are case-sensitive and diacritic sensitive:但是，聚合表达式$regexFind忽略排序规则；也就是说，以下正则表达式模式匹配示例区分大小写和变音符号：

db.myColl.aggregate( [ { $addFields: { results: { $regexFindAll: { input: "$category", regex: /cafe/ }  } } } ] )
db.myColl.aggregate(
   [ { $addFields: { results: { $regexFindAll: { input: "$category", regex: /cafe/ }  } } } ],
   { collation: { locale: "fr", strength: 1 } }       // Ignored in the $regexFindAll
)

Both operations return the following:两个操作都返回以下内容：

{ "_id" : 1, "category" : "café", "results" : [ ] }
{ "_id" : 2, "category" : "cafe", "results" : [ { "match" : "cafe", "idx" : 0, "captures" : [ ] } ] }
{ "_id" : 3, "category" : "cafE", "results" : [ ] }

To perform a case-insensitive regex pattern matching, use the i Option instead. See i Option for an example.要执行不区分大小写的regex模式匹配，请改用i选项。有关示例，请参阅i选项。

captures Output Behavior输出行为

If your regex pattern contains capture groups and the pattern finds a match in the input, the captures array in the results corresponds to the groups captured by the matching string. 如果regex模式包含捕获组，并且该模式在input中找到匹配项，则结果中的捕获数组与匹配字符串捕获的组相对应。Capture groups are specified with unescaped parentheses () in the regex pattern. 捕获组是用regex模式中未加括号的括号()指定的。The length of the captures array equals the number of capture groups in the pattern and the order of the array matches the order in which the capture groups appear.captures数组的长度等于模式中捕获组的数量，并且数组的顺序与捕获组的出现顺序相匹配。

Create a sample collection named contacts with the following documents:使用以下文档创建名为contacts的示例集合：

db.contacts.insertMany([
  { "_id": 1, "fname": "Carol", "lname": "Smith", "phone": "718-555-0113" },
  { "_id": 2, "fname": "Daryl", "lname": "Doe", "phone": "212-555-8832" },
  { "_id": 3, "fname": "Polly", "lname": "Andrews", "phone": "208-555-1932" },
  { "_id": 4, "fname": "Colleen", "lname": "Duncan", "phone": "775-555-0187" },
  { "_id": 5, "fname": "Luna", "lname": "Clarke", "phone": "917-555-4414" }
])

The following pipeline applies the regex pattern /(C(ar)*)ol/ to the fname field:以下管道将regex模式/(C(ar)*)ol/应用于fname字段：

db.contacts.aggregate([
  {
    $project: {
      returnObject: {
        $regexFindAll: { input: "$fname", regex: /(C(ar)*)ol/ }
      }
    }
  }
])

The regex pattern finds a match with fname values Carol and Colleen:regex模式查找与fname值Carol和Colleen匹配的值：

{ "_id" : 1, "returnObject" : [ { "match" : "Carol", "idx" : 0, "captures" : [ "Car", "ar" ] } ] }
{ "_id" : 2, "returnObject" : [ ] }
{ "_id" : 3, "returnObject" : [ ] }
{ "_id" : 4, "returnObject" : [ { "match" : "Col", "idx" : 0, "captures" : [ "C", null ] } ] }
{ "_id" : 5, "returnObject" : [ ] }

The pattern contains the capture group (C(ar)*) which contains the nested group (ar). 该模式包含捕获组(C(ar)*)，该捕获组包含嵌套组(ar)。The elements in the captures array correspond to the two capture groups. captures数组中的元素对应于两个捕获组。If a matching document is not captured by a group (e.g. Colleen and the group (ar)), $regexFindAll replaces the group with a null placeholder.如果一个组（例如Colleen和组(ar)）没有捕获匹配的文档，$regexFindAll将用null占位符替换该组。

As shown in the previous example, the captures array contains an element for each capture group (using null for non-captures). 如前一个示例所示，captures数组包含每个捕获组的一个元素（对非捕获使用null）。Consider the following example which searches for phone numbers with New York City area codes by applying a logical or of capture groups to the phone field. 考虑以下示例，该示例通过将逻辑or捕获组应用于phone字段来搜索具有纽约市区号的电话号码。Each group represents a New York City area code:每组代表一个纽约市区号：

db.contacts.aggregate([
  {
    $project: {
      nycContacts: {
        $regexFindAll: { input: "$phone", regex: /^(718).*|^(212).*|^(917).*/ }
      }
    }
  }
])

For documents which are matched by the regex pattern, the captures array includes the matching capture group and replaces any non-capturing groups with null:对于regex模式匹配的文档，captures数组包括匹配的捕获组，并将任何非捕获组替换为null：

{ "_id" : 1, "nycContacts" : [ { "match" : "718-555-0113", "idx" : 0, "captures" : [ "718", null, null ] } ] }
{ "_id" : 2, "nycContacts" : [ { "match" : "212-555-8832", "idx" : 0, "captures" : [ null, "212", null ] } ] }
{ "_id" : 3, "nycContacts" : [ ] }
{ "_id" : 4, "nycContacts" : [ ] }
{ "_id" : 5, "nycContacts" : [ { "match" : "917-555-4414", "idx" : 0, "captures" : [ null, null, "917" ] } ] }

Examples实例

$regexFindAll and Its Options及其选项

To illustrate the behavior of the $regexFindAll operator as discussed in this example, create a sample collection products with the following documents:为了说明本例中讨论的$regexFindAll运算符的行为，请使用以下文档创建一个示例集合products：

db.products.insertMany([
   { _id: 1, description: "Single LINE description." },
   { _id: 2, description: "First lines\nsecond line" },
   { _id: 3, description: "Many spaces before     line" },
   { _id: 4, description: "Multiple\nline descriptions" },
   { _id: 5, description: "anchors, links and hyperlinks" },
   { _id: 6, description: "métier work vocation" }
])

By default, $regexFindAll performs a case-sensitive match. 默认情况下，$regexFindAll执行区分大小写的匹配。For example, the following aggregation performs a case-sensitive $regexFindAll on the description field. 例如，以下聚合对description字段执行区分大小写的$regexFindAll。The regex pattern /line/ does not specify any grouping:正则表达式模式/line/未指定任何分组：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex: /line/ } } } }
])

The operation returns the following:该操作返回以下内容：

{
   "_id" : 1,
   "description" : "Single LINE description.",
   "returnObject" : [ ]
}
{
   "_id" : 2,
   "description" : "First lines\nsecond line",
   "returnObject" : [ { "match" : "line", "idx" : 6, "captures" : [ ]}, { "match" : "line", "idx" : 19, "captures" : [ ] } ]
}
{
   "_id" : 3,
   "description" : "Many spaces before     line",
   "returnObject" : [ { "match" : "line", "idx" : 23, "captures" : [ ] } ]
}
{
   "_id" : 4,
   "description" : "Multiple\nline descriptions",
   "returnObject" : [ { "match" : "line", "idx" : 9, "captures" : [ ] }
] }

{
   "_id" : 5,
   "description" : "anchors, links and hyperlinks",
   "returnObject" : [ ]
}
{
   "_id" : 6,
   "description" : "métier work vocation",
   "returnObject" : [ ]
}

The following regex pattern /lin(e|k)/ specifies a grouping (e|k) in the pattern:以下regex模式/lin(e|k)/指定模式中的分组(e|k)：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex: /lin(e|k)/ } } } }
])

The operation returns the following:该操作返回以下内容：

{
   "_id" : 1,
   "description" : "Single LINE description.",
   "returnObject": [ ]
}
{
   "_id" : 2,
   "description" : "First lines\nsecond line",
   "returnObject" : [ { "match" : "line", "idx" : 6, "captures" : [ "e" ] }, { "match" : "line", "idx" : 19, "captures" : [ "e" ] } ]
}
{
   "_id" : 3,
   "description" : "Many spaces before     line",
   "returnObject" : [ { "match" : "line", "idx" : 23, "captures" : [ "e" ] } ]
}
{
   "_id" : 4,
   "description" : "Multiple\nline descriptions",
   "returnObject" : [ { "match" : "line", "idx" : 9, "captures" : [ "e" ] } ]
}
{
   "_id" : 5,
   "description" : "anchors, links and hyperlinks",
   "returnObject" : [ { "match" : "link", "idx" : 9, "captures" : [ "k" ] }, { "match" : "link", "idx" : 24, "captures" : [ "k" ] } ]
}
{
   "_id" : 6,
   "description" : "métier work vocation",
   "returnObject" : [ ]
}

In the return option, the idx field is the code point index and not the byte index. 在return选项中，idx字段是代码点索引，而不是字节索引。To illustrate, consider the following example that uses the regex pattern /tier/:为了进行说明，请考虑以下使用正则表达式模式/tier/的示例：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex: /tier/ } } } }
])

The operation returns the following where only the last record matches the pattern and the returned idx is 2 (instead of 3 if using a byte index)该操作返回以下内容，其中只有最后一条记录与模式匹配，并且返回的idx为2（如果使用字节索引，则为3）

{ "_id" : 1, "description" : "Single LINE description.", "returnObject" : [ ] }
{ "_id" : 2, "description" : "First lines\nsecond line", "returnObject" : [ ] }
{ "_id" : 3, "description" : "Many spaces before     line", "returnObject" : [ ] }
{ "_id" : 4, "description" : "Multiple\nline descriptions", "returnObject" : [ ] }
{ "_id" : 5, "description" : "anchors, links and hyperlinks", "returnObject" : [ ] }
{ "_id" : 6, "description" : "métier work vocation",
             "returnObject" : [ { "match" : "tier", "idx" : 2, "captures" : [ ] } ] }

i Option选项

Note

You cannot specify options in both the regex and the options field.不能在regex和options字段中都指定选项。

To perform case-insensitive pattern matching, include the i option as part of the regex field or in the options field:要执行不区分大小写的模式匹配，请将i选项作为regex字段或options字段的一部分：

// Specify i as part of the regex field
{ $regexFindAll: { input: "$description", regex: /line/i } }

// Specify i in the options field
{ $regexFindAll: { input: "$description", regex: /line/, options: "i" } }
{ $regexFindAll: { input: "$description", regex: "line", options: "i" } }

For example, the following aggregation performs a case-insensitive $regexFindAll on the description field. 例如，以下聚合对描述字段执行不区分大小写的$regexFindAll。The regex pattern /line/ does not specify any grouping:正则表达式模式/line/未指定任何分组：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex: /line/i } } } }
])

The operation returns the following documents:该操作返回以下文档：

{
   "_id" : 1,
   "description" : "Single LINE description.",
   "returnObject" : [ { "match" : "LINE", "idx" : 7, "captures" : [ ] } ]
}
{
   "_id" : 2,
   "description" : "First lines\nsecond line",
   "returnObject" : [ { "match" : "line", "idx" : 6, "captures" : [ ] }, { "match" : "line", "idx" : 19, "captures" : [ ] } ]
}
{
   "_id" : 3,
   "description" : "Many spaces before     line",
   "returnObject" : [ { "match" : "line", "idx" : 23, "captures" : [ ] } ]
}
{
   "_id" : 4,
   "description" : "Multiple\nline descriptions",
   "returnObject" : [ { "match" : "line", "idx" : 9, "captures" : [ ] } ]
}
{
   "_id" : 5,
   "description" : "anchors, links and hyperlinks",
   "returnObject" : [ ]
}
{ "_id" : 6, "description" : "métier work vocation", "returnObject" : [ ] }

m Option选项

Note

You cannot specify options in both the regex and the options field.不能在regex和options字段中都指定选项。

To match the specified anchors (e.g. ^, $) for each line of a multiline string, include the m option as part of the regex field or in the options field:要为多行字符串的每一行匹配指定的锚点（例如^、$），请将m选项作为regex字段或options字段的一部分：

// Specify m as part of the regex field
{ $regexFindAll: { input: "$description", regex: /line/m } }

// Specify m in the options field
{ $regexFindAll: { input: "$description", regex: /line/, options: "m" } }
{ $regexFindAll: { input: "$description", regex: "line", options: "m" } }

The following example includes both the i and the m options to match lines starting with either the letter s or S for multiline strings:以下示例包括i和m选项，用于匹配多行字符串中以字母s或S开头的行：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex: /^s/im } } } }
])

The operation returns the following:该操作返回以下内容：

{
   "_id" : 1,
   "description" : "Single LINE description.",
   "returnObject" : [ { "match" : "S", "idx" : 0, "captures" : [ ] } ]
}
{
   "_id" : 2,
   "description" : "First lines\nsecond line",
   "returnObject" : [ { "match" : "s", "idx" : 12, "captures" : [ ] } ]
}
{
   "_id" : 3,
   "description" : "Many spaces before     line",
   "returnObject" : [ ]
}
{
   "_id" : 4,
   "description" : "Multiple\nline descriptions",
   "returnObject" : [ ]
}
{
   "_id" : 5,
   "description" : "anchors, links and hyperlinks",
   "returnObject" : [ ]
}
{ "_id" : 6, "description" : "métier work vocation", "returnObject" : [ ] }

x Option

Note

You cannot specify options in both the regex and the options field.不能在regex和options字段中都指定选项。

To ignore all unescaped white space characters and comments (denoted by the un-escaped hash # character and the next new-line character) in the pattern, include the s option in the options field:要忽略模式中所有未转义的空白字符和注释（由未转义的hash#字符和下一个换行符表示），请在options字段中包含s选项：

// Specify x in the options field
{ $regexFindAll: { input: "$description", regex: /line/, options: "x" } }
{ $regexFindAll: { input: "$description", regex: "line", options: "x" } }

The following example includes the x option to skip unescaped white spaces and comments:以下示例包括用于跳过未跳过的空白和注释的x选项：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex: /lin(e|k) # matches line or link/, options:"x" } } } }
])

The operation returns the following:该操作返回以下内容：

{
   "_id" : 1,
   "description" : "Single LINE description.",
   "returnObject" : [ ]
}
{
   "_id" : 2,
   "description" : "First lines\nsecond line",
   "returnObject" : [ { "match" : "line", "idx" : 6, "captures" : [ "e" ] }, { "match" : "line", "idx" : 19, "captures" : [ "e" ] } ]
}
{
   "_id" : 3,
   "description" : "Many spaces before     line",
   "returnObject" : [ { "match" : "line", "idx" : 23, "captures" : [ "e" ] } ]
}
{
   "_id" : 4,
   "description" : "Multiple\nline descriptions",
   "returnObject" : [ { "match" : "line", "idx" : 9, "captures" : [ "e" ] } ]
}
{
   "_id" : 5,
   "description" : "anchors, links and hyperlinks",
   "returnObject" : [ { "match" : "link", "idx" : 9, "captures" : [ "k" ] }, { "match" : "link", "idx" : 24, "captures" : [ "k" ] } ]
}
{ "_id" : 6, "description" : "métier work vocation", "returnObject" : [ ] }

s Option

Note

You cannot specify options in both the regex and the options field.不能在regex和options字段中都指定选项。

To allow the dot character (i.e. .) in the pattern to match all characters including the new line character, include the s option in the options field:要允许模式中的点字符（即.）与包括换行符在内的所有字符匹配，请在options字段中包含s选项：

// Specify s in the options field
{ $regexFindAll: { input: "$description", regex: /m.*line/, options: "s" } }
{ $regexFindAll: { input: "$description", regex: "m.*line", options: "s" } }

The following example includes the s option to allow the dot character (i.e. .) to match all characters including new line as well as the i option to perform a case-insensitive match:以下示例包括允许点字符（即.）匹配包括新行在内的所有字符的s选项，以及执行不区分大小写匹配的i选项：

db.products.aggregate([
   { $addFields: { returnObject: { $regexFindAll: { input: "$description", regex:/m.*line/, options: "si"  } } } }
])

The operation returns the following:该操作返回以下内容：

{
   "_id" : 1,
   "description" : "Single LINE description.",
   "returnObject" : [ ]
}
{
   "_id" : 2,
   "description" : "First lines\nsecond line",
   "returnObject" : [ ]
}
{
   "_id" : 3,
   "description" : "Many spaces before     line",
   "returnObject" : [ { "match" : "Many spaces before line", "idx" : 0, "captures" : [ ] } ]
}
{
   "_id" : 4,
   "description" : "Multiple\nline descriptions",
   "returnObject" : [ { "match" : "Multiple\nline", "idx" : 0, "captures" : [ ] } ]
}
{
   "_id" : 5,
   "description" : "anchors, links and hyperlinks",
   "returnObject" : [ ]
}
{ "_id" : 6, "description" : "métier work vocation", "returnObject" : [ ] }

Use $regexFindAll to Parse Email from String使用$regexFindAll从字符串分析电子邮件

Create a sample collection feedback with the following documents:使用以下文档创建示例集合feedback：

db.feedback.insertMany([
   { "_id" : 1, comment: "Hi, I'm just reading about MongoDB -- aunt.arc.tica@example.com"  },
   { "_id" : 2, comment: "I wanted to concatenate a string" },
   { "_id" : 3, comment: "How do I convert a date to string? Contact me at either cam@mongodb.com or c.dia@mongodb.com" },
   { "_id" : 4, comment: "It's just me. I'm testing.  fred@MongoDB.com" }
])

The following aggregation uses the $regexFindAll to extract all emails from the comment field (case insensitive).以下聚合使用$regexFindAll从comment字段中提取所有电子邮件（不区分大小写）。

db.feedback.aggregate( [
    { $addFields: {
       "email": { $regexFindAll: { input: "$comment", regex: /[a-z0-9_.+-]+@[a-z0-9_.+-]+\.[a-z0-9_.+-]+/i } }
    } },
    { $set: { email: "$email.match"} }
] )
First Stage第一阶段

The stage uses the $addFields stage to add a new field email to the document. 该阶段使用$addFields阶段将新的字段电子邮件添加到文档中。The new field is an array that contains the result of performing the $regexFindAll on the comment field:新字段是一个数组，包含对comment字段执行$regexFindAll的结果：

{ "_id" : 1, "comment" : "Hi, I'm just reading about MongoDB -- aunt.arc.tica@example.com", "email" : [ { "match" : "aunt.arc.tica@example.com", "idx" : 38, "captures" : [ ] } ] }
{ "_id" : 2, "comment" : "I wanted to concatenate a string", "email" : [ ] }
{ "_id" : 3, "comment" : "How do I convert a date to string? Contact me at either cam@mongodb.com or c.dia@mongodb.com", "email" : [ { "match" : "cam@mongodb.com", "idx" : 56, "captures" : [ ] }, { "match" : "c.dia@mongodb.com", "idx" : 75, "captures" : [ ] } ] }
{ "_id" : 4, "comment" : "It's just me. I'm testing.  fred@MongoDB.com", "email" : [ { "match" : "fred@MongoDB.com", "idx" : 28, "captures" : [ ] } ] }
Second Stage第二阶段

The stage use the $set stage to reset the email array elements to the "email.match" value(s). 该阶段使用$set阶段将email数组元素重置为"email.match"值。If the current value of email is null, the new value of email is set to null.如果email的当前值为null，则将email的新值设置为null。

{ "_id" : 1, "comment" : "Hi, I'm just reading about MongoDB -- aunt.arc.tica@example.com", "email" : [ "aunt.arc.tica@example.com" ] }
{ "_id" : 2, "comment" : "I wanted to concatenate a string", "email" : [ ] }
{ "_id" : 3, "comment" : "How do I convert a date to string? Contact me at either cam@mongodb.com or c.dia@mongodb.com", "email" : [ "cam@mongodb.com", "c.dia@mongodb.com" ] }
{ "_id" : 4, "comment" : "It's just me. I'm testing.  fred@MongoDB.com", "email" : [ "fred@MongoDB.com" ] }

Use Captured Groupings to Parse User Name使用捕获的分组分析用户名

Create a sample collection feedback with the following documents:使用以下文档创建示例集合feedback：

db.feedback.insertMany([
   { "_id" : 1, comment: "Hi, I'm just reading about MongoDB -- aunt.arc.tica@example.com"  },
   { "_id" : 2, comment: "I wanted to concatenate a string" },
   { "_id" : 3, comment: "How do I convert a date to string? Contact me at either cam@mongodb.com or c.dia@mongodb.com" },
   { "_id" : 4, comment: "It's just me. I'm testing.  fred@MongoDB.com" }
])

To reply to the feedback, assume you want to parse the local-part of the email address to use as the name in the greetings. 要回复反馈，假设您想解析电子邮件地址的本地部分，用作问候语中的名称。Using the captured field returned in the $regexFindAll results, you can parse out the local part of each email address:使用$regexFindAll结果中返回的captured字段，您可以解析出每个电子邮件地址的本地部分：

db.feedback.aggregate( [
    { $addFields: {
       "names": { $regexFindAll: { input: "$comment", regex: /([a-z0-9_.+-]+)@[a-z0-9_.+-]+\.[a-z0-9_.+-]+/i } },
    } },
    { $set: { names: { $reduce: { input:  "$names.captures", initialValue: [ ], in: { $concatArrays: [ "$$value", "$$this" ] } } } } }
] )
First Stage第一阶段

The stage uses the $addFields stage to add a new field names to the document. 该阶段使用$addFields阶段向文档添加新的字段names。The new field contains the result of performing the $regexFindAll on the comment field:新字段包含对comment字段执行$regexFindAll的结果：

{
   "_id" : 1,
   "comment" : "Hi, I'm just reading about MongoDB -- aunt.arc.tica@example.com",
   "names" : [ { "match" : "aunt.arc.tica@example.com", "idx" : 38, "captures" : [ "aunt.arc.tica" ] } ]
}

{ "_id" : 2, "comment" : "I wanted to concatenate a string", "names" : [ ] }
{
   "_id" : 3,
   "comment" : "How do I convert a date to string? Contact me at either cam@mongodb.com or c.dia@mongodb.com",
   "names" : [
      { "match" : "cam@mongodb.com", "idx" : 56, "captures" : [ "cam" ] },
      { "match" : "c.dia@mongodb.com", "idx" : 75, "captures" : [ "c.dia" ] }
    ]
}
{
   "_id" : 4,
   "comment" : "It's just me. I'm testing.  fred@MongoDB.com",
   "names" : [ { "match" : "fred@MongoDB.com", "idx" : 28, "captures" : [ "fred" ] } ]
}
Second Stage第二阶段

The stage use the $set stage with the $reduce operator to reset names to an array that contains the "$names.captures" elements.该阶段使用带有$reduce运算符的$set阶段将names重置为包含"$names.captures"元素的数组。

{
   "_id" : 1,
   "comment" : "Hi, I'm just reading about MongoDB -- aunt.arc.tica@example.com",
   "names" : [ "aunt.arc.tica" ]
}
{ "_id" : 2, "comment" : "I wanted to concatenate a string", "names" : [ ] }
{
   "_id" : 3,
   "comment" : "How do I convert a date to string? Contact me at either cam@mongodb.com or c.dia@mongodb.com",
   "names" : [ "cam", "c.dia" ]
}
{
   "_id" : 4,
   "comment" : "It's just me. I'm testing.  fred@MongoDB.com",
   "names" : [ "fred" ]
}
Tip

See also: 另请参阅：

For more information on the behavior of the captures array and additional examples, see captures Output Behavior.有关captures数组行为的更多信息和其他示例，请参阅captures输出行为。