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$setIntersection（表达式操作符）

定义

$setIntersection

接收两个或多个数组，并返回一个数组，其中包含出现在每个输入数组中的元素。

$setIntersection 通过以下语法实现：

{ $setIntersection: [ <expression1>, <expression2>, ... ] }

如果参数各自解析为一个数组，则它们可以是任何有效的表达式。有关表达式的更多信息，请参阅表达式。

行为

$setIntersection performs set operation on arrays, treating arrays as sets. If an array contains duplicate entries, $setIntersection ignores the duplicate entries. $setIntersection ignores the order of the elements.

$setIntersection 过滤掉结果中的重复项，以输出仅包含唯一条目的大量。输出大量中元素的顺序未指定。

If no intersections are found (i.e. the input arrays contain no common elements), $setIntersection returns an empty array.

If a set contains a nested array element, $setIntersection does not descend into the nested array but evaluates the array at top-level.

例子

结果

注意

{ $setIntersection: [
  [ "a", "c" ],
  [ "a", "b" ]
] }

[ "a" ]

两个数组之间唯一的共同元素是 "a"。

{ $setIntersection: [
  [ "a", "c" ],
  [ "a", "b", "c" ]
] }

[ "a", "c" ]

"a" 和 "c" 是两个数组之间的公共元素。

{ $setIntersection: [
  [ "a", "b", "a" ],
  [ "b", "a" ]
] }

[ "b", "a" ]

"b" 和 "a" 是两个数组之间的公共元素。

{ $setIntersection: [
  [ "a", "b" ],
  [ [ "a", "b" ] ]
] }

[ ]

两个数组之间没有共同元素。字符串元素 "a" 和 "b" 不等于大量[ "a", "b" ]。

{ $setIntersection: [
  [ ],
  [ "a", "b" ]
] }

[ ]

由于第一个大量为空，因此两个数组之间没有共同元素。

{ $setIntersection: [
  [ "a", "a" ],
  [ "a", "b" ]
] }

[ "a" ]

唯一的共同元素是 "a"，它会在结果中出现一次，因为只考虑唯一元素。

示例

本部分包含展示如何将 $setIntersection 与集合一起使用的示例。

元素数组示例

考虑包含以下文档的 flowers 集合：

db.flowers.insertMany( [
   { "_id" : 1, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid" ] },
   { "_id" : 2, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "orchid", "rose", "orchid" ] },
   { "_id" : 3, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid", "jasmine" ] },
   { "_id" : 4, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "jasmine", "rose" ] },
   { "_id" : 5, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ ] },
   { "_id" : 6, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose" ], [ "orchid" ] ] },
   { "_id" : 7, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose", "orchid" ] ] },
   { "_id" : 8, "flowerFieldA" : [ ], "flowerFieldB" : [ ] },
   { "_id" : 9, "flowerFieldA" : [ ], "flowerFieldB" : [ "rose" ] }
] )

The following operation uses the $setIntersection operator to return an array of elements common to both the flowerFieldA array and the flowerFieldB array:

db.flowers.aggregate(
   [
     { $project: { flowerFieldA: 1, flowerFieldB: 1, commonToBoth: { $setIntersection: [ "$flowerFieldA", "$flowerFieldB" ] }, _id: 0 } }
   ]
)

操作返回以下结果：

{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid" ], "commonToBoth" : [ "orchid", "rose" ] }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "orchid", "rose", "orchid" ], "commonToBoth" : [ "orchid", "rose" ] }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid", "jasmine" ], "commonToBoth" : [ "orchid", "rose" ] }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "jasmine", "rose" ], "commonToBoth" : [ "rose" ] }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ ], "commonToBoth" : [ ] }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose" ], [ "orchid" ] ], "commonToBoth" : [ ] }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose", "orchid" ] ], "commonToBoth" : [ ] }
{ "flowerFieldA" : [ ], "flowerFieldB" : [ ], "commonToBoth" : [ ] }
{ "flowerFieldA" : [ ], "flowerFieldB" : [ "rose" ], "commonToBoth" : [ ] }

检索授予当前用户的角色相关的文档

从 MongoDB 7.0 开始，您可以使用新的 USER_ROLES 系统变量来返回用户角色。

本部分的场景显示了具有各种角色的用户，而这些用户对包含预算信息的集合中的文档具有有限访问权限。

该场景显示了 USER_ROLES 的一种可能用途。budget 集合包含带有名为 allowedRoles 字段的文档。正如以下场景所示，您可以编写查询将 allowedRoles 字段中找到的用户角色与 USER_ROLES 系统变量返回的角色进行比较。

注意

有关另一个 USER_ROLES 示例场景，请参阅检索授予当前用户的角色相关的医疗信息。该示例不会将用户角色存储在文档字段中，如以下示例所示。

对于本部分中的预算方案，请执行以下步骤来创建角色、用户和 budget 集合：

创建角色

运行：

db.createRole( { role: "Marketing", roles: [], privileges: [] } )
db.createRole( { role: "Sales", roles: [], privileges: [] } )
db.createRole( { role: "Development", roles: [], privileges: [] } )
db.createRole( { role: "Operations", roles: [], privileges: [] } )

创建用户

创建名为 John 和 Jane 的用户，并赋予所需角色。将 test 数据库替换为您的数据库名称。

db.createUser( {
   user: "John",
   pwd: "jn008",
   roles: [
      { role: "Marketing", db: "test" },
      { role: "Development", db: "test" },
      { role: "Operations", db: "test" },
      { role: "read", db: "test" }
   ]
} )
db.createUser( {
   user: "Jane",
   pwd: "je009",
   roles: [
      { role: "Sales", db: "test" },
      { role: "Operations", db: "test" },
      { role: "read", db: "test" }
   ]
} )

创建集合

运行：

db.budget.insertMany( [
   {
      _id: 0,
      allowedRoles: [ "Marketing" ],
      comment: "For marketing team",
      yearlyBudget: 15000
   },
   {
      _id: 1,
      allowedRoles: [ "Sales" ],
      comment: "For sales team",
      yearlyBudget: 17000,
      salesEventsBudget: 1000
   },
   {
      _id: 2,
      allowedRoles: [ "Operations" ],
      comment: "For operations team",
      yearlyBudget: 19000,
      cloudBudget: 12000
   },
   {
      _id: 3,
      allowedRoles: [ "Development" ],
      comment: "For development team",
      yearlyBudget: 27000
   }
] )

执行以下步骤以检索 John 可以访问的文档：

以 John 身份登录

运行：

db.auth( "John", "jn008" )

检索文档

要使用系统变量，请将$$添加到变量名称的开头。将USER_ROLES系统变量指定为$$USER_ROLES。

运行：

db.budget.aggregate( [ {
   $match: {
      $expr: {
         $not: {
            $eq: [ { $setIntersection: [ "$allowedRoles", "$$USER_ROLES.role" ] }, [] ]
         }
      }
   }
} ] )

The previous example returns the documents from the budget collection that match at least one of the roles that the user who runs the example has. To do that, the example uses $setIntersection to return documents where the intersection between the budget document allowedRoles field and the set of user roles from $$USER_ROLES is not empty.

检查文档

John 具有Marketing、Operations和Development 角色，且能看到以下文档：

[
   {
      _id: 0,
      allowedRoles: [ 'Marketing' ],
      comment: 'For marketing team',
      yearlyBudget: 15000
   },
   {
      _id: 2,
      allowedRoles: [ 'Operations' ],
      comment: 'For operations team',
      yearlyBudget: 19000,
      cloudBudget: 12000
   },
   {
      _id: 3,
      allowedRoles: [ 'Development' ],
      comment: 'For development team',
      yearlyBudget: 27000
   }
]

执行以下步骤以检索 Jane 可以访问的文档：

以 Jane 身份登录

运行：

db.auth( "Jane", "je009" )

检索文档

要使用系统变量，请将$$添加到变量名称的开头。将USER_ROLES系统变量指定为$$USER_ROLES。

运行：

db.budget.aggregate( [ {
   $match: {
      $expr: {
         $not: {
            $eq: [ { $setIntersection: [ "$allowedRoles", "$$USER_ROLES.role" ] }, [] ]
         }
      }
   }
} ] )

检查文档

Jane 具有 Sales和 Operations 角色，且能看到以下文档：

[
   {
      _id: 1,
      allowedRoles: [ 'Sales' ],
      comment: 'For sales team',
      yearlyBudget: 17000,
      salesEventsBudget: 1000
   },
   {
      _id: 2,
      allowedRoles: [ 'Operations' ],
      comment: 'For operations team',
      yearlyBudget: 19000,
      cloudBudget: 12000
   }
]

注意

在分片集群上，查询可以由另一个服务器节点代表用户在分片上运行。在这些查询中，USER_ROLES 仍填充用户的角色。