$setIsSubset (聚合)

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定义

行为
示例

定义

$setIsSubset

接收两个数组，当第一个数组是第二个数组的子集（包括第一个数组等于第二个数组时）返回 true，否则返回 false。

$setIsSubset 的语法如下

{ $setIsSubset: [ <expression1>, <expression2> ] }

参数可以是任何有效的表达式，只要它们每个解析为数组。有关表达式更多信息，请参阅表达式操作符。

行为

$setIsSubset 对数组执行集合运算，将数组视为集合。如果数组包含重复条目，$setIsSubset 忽略重复条目。 $setIsSubset 忽略元素的顺序。

如果集合包含嵌套数组元素，$setIsSubset 不会进入嵌套数组，而是在顶层评估数组。

示例

结果

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

true

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

false

示例

考虑一个包含以下文档的 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" ] }
] )

以下操作使用 $setIsSubset 操作符来判断 flowerFieldA 数组是否是 flowerFieldB 数组的子集

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

操作返回以下结果

{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid" ], "AisSubset" : true }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "orchid", "rose", "orchid" ], "AisSubset" : true }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid", "jasmine" ], "AisSubset" : true }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "jasmine", "rose" ], "AisSubset" : false }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ ], "AisSubset" : false }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose" ], [ "orchid" ] ], "AisSubset" : false }
{ "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose", "orchid" ] ], "AisSubset" : false }
{ "flowerFieldA" : [ ], "flowerFieldB" : [ ], "AisSubset" : true }
{ "flowerFieldA" : [ ], "flowerFieldB" : [ "rose" ], "AisSubset" : true }

$setIntersection

$setUnion