$redact (aggregation)

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:预测集合包含以下格式的文档，其中tags字段列出了该文档/嵌入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：

{
  _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 section3.",
        tags: [ "HCS" ]
      }
    }
  ]
}

A user has access to view information with either the tag "STLW" or "G". 用户可以使用标签"STLW""G"查看信息。To run a query on all documents with year 2014 for this user, include a $redact stage as in the following:要为该用户运行2014年所有文档的查询，请包括$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“修订”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：

{
  _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.在本示例文档中，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 allfields contained in a document/embedded document at level 5, include a $redact stage that specifies the system variable "$$PRUNE" in the then field:要对状态为A的所有文档运行查询，并排除级别5的文档/嵌入文档中包含的所有字段，请包括一个$redact阶段，该阶段在then字段中指定系统变量"$$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level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值的嵌入文档，例如shipping_addr字段。

The aggregation operation returns the following "redacted" document:聚合操作返回以下“修订”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阶段整体上排除了字段cc，包括shipping_addr字段，该字段包含级别字段值等于3而不是5的嵌入文档。