$redact (aggregation stage)（聚合阶段）

Evaluate Access at Every Document Level评估每个文档级别的访问权限

A forecasts collection contains documents of the following form where the tags field lists the different access values for that document/embedded document level; i.e. a value of [ "G", "STLW" ] specifies either "G" or "STLW" can access the data:forecasts（预测）集合包含以下形式的文档，其中标签字段列出了该文档/嵌入式文档级别的不同访问值；即，值[ "G", "STLW" ]指定"G"或"STLW"可以访问数据：

db.forecasts.insertOne(
   {
      _id: 1,
      title: "123 Department Report",
      tags: [ "G", "STLW" ],
      year: 2014,
      subsections: [
         {
         subtitle: "Section 1: Overview",
         tags: [ "SI", "G" ],
         content:  "Section 1: This is the content of section 1."
         },
         {
         subtitle: "Section 2: Analysis",
         tags: [ "STLW" ],
         content: "Section 2: This is the content of section 2."
         },
         {
         subtitle: "Section 3: Budgeting",
         tags: [ "TK" ],
         content: {
            text: "Section 3: This is the content of section 3.",
            tags: [ "HCS" ]
         }
         }
      ]
   }
)

A user has access to view information with either the tag "STLW" or "G". To run a query on all documents with year 2014 for this user, include a $redact stage as in the following:用户可以使用标签"STLW"或"G"查看信息。要对该用户2014年的所有文档运行查询，请包含一个$redact阶段，如下所示：

var userAccess = [ "STLW", "G" ];
db.forecasts.aggregate(
   [
   { $match: { year: 2014 } },
   { $redact: {
      $cond: {
         if: { $gt: [ { $size: { $setIntersection: [ "$tags", userAccess ] } }, 0 ] },
         then: "$$DESCEND",
         else: "$$PRUNE"
         }
      }
   }
   ]
);

The aggregation operation returns the following "redacted" document:聚合操作返回以下“已编辑”文档：

{
   _id: 1,
   title: "123 Department Report",
   tags: [ "G", "STLW" ],
   year: 2014,
   subsections: [
      {
      subtitle: "Section 1: Overview",
      tags: [ "SI", "G" ],
      content: "Section 1: This is the content of section 1."
      },
      {
      subtitle: "Section 2: Analysis",
      tags: [ "STLW" ],
      content : "Section 2: This is the content of section 2."
      }
   ]
}

Exclude All Fields at a Given Level排除给定级别的所有字段

A collection accounts contains the following document:集合accounts包含以下文档：

db.accounts.insertOne(
   {
      _id: 1,
      level: 1,
      acct_id: "xyz123",
      cc: {
         level: 5,
         type: "yy",
         num: 000000000000,
         exp_date: ISODate("2015-11-01T00:00:00.000Z"),
         billing_addr: {
         level: 5,
         addr1: "123 ABC Street",
         city: "Some City"
         },
         shipping_addr: [
         {
            level: 3,
            addr1: "987 XYZ Ave",
            city: "Some City"
         },
         {
            level: 3,
            addr1: "PO Box 0123",
            city: "Some City"
         }
         ]
      },
      status: "A"
   }
)

In this example document, the level field determines the access level required to view the data.在此示例文档中，level字段确定查看数据所需的访问级别。

To run a query on all documents with status A and exclude all fields contained in a document/embedded document at level 5, include a $redact stage that specifies the system variable "$$PRUNE" in the then field:要对状态为A的所有文档运行查询，并排除级别5的文档/嵌入文档中包含的所有字段，请在then字段中包含一个$redact阶段，指定系统变量"$$PRUNE"：

db.accounts.aggregate(
   [
      { $match: { status: "A" } },
      {
         $redact: {
         $cond: {
            if: { $eq: [ "$level", 5 ] },
            then: "$$PRUNE",
            else: "$$DESCEND"
         }
         }
      }
   ]
);

The $redact stage evaluates the level field to determine access. $redact阶段评估级别字段以确定访问权限。If the level field equals 5, then exclude all fields at that level, even if the excluded field contains embedded documents that may have different level values, such as the shipping_addr field.如果level字段等于5，则排除该级别的所有字段，即使排除的字段包含可能具有不同level值的嵌入式文档，例如shipping_addr字段。

The aggregation operation returns the following "redacted" document:聚合操作返回以下“已编辑”文档：

{
   _id: 1,
   level: 1,
   acct_id: "xyz123",
   status: "A"
}

The result set shows that the $redact stage excluded the field cc as a whole, including the shipping_addr field which contained embedded documents that had level field values equal to 3 and not 5.结果集显示，$redact阶段将字段cc作为一个整体排除在外，包括shipping_addr字段，该字段包含level（级别）字段值等于3而不是5的嵌入式文档。