$setIsSubset (aggregation)

在本页面

Definition

接受两个数组,当第一个数组是第二个数组的子集时(包括第一个数组等于第二个数组时),返回true,否则返回false

$setIsSubset具有以下语法:

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

参数可以是任何有效的expression,只要它们每个都解析为数组即可。有关表达式的更多信息,请参见Expressions

Behavior

$setIsSubset对数组执行 set 操作,将数组视为 set。如果数组包含重复项,则$setIsSubset会忽略重复项。 $setIsSubset忽略元素的 Sequences。

如果集合包含嵌套数组元素,则$setIsSubset不会*降级到嵌套数组中,而是在顶级对数组进行求值。

Example Result
{ $setIsSubset: [ [ "a", "b", "a" ], [ "b", "a" ] ] } true
{ $setIsSubset: [ [ "a", "b" ], [ [ "a", "b" ] ] ] } false

Example

考虑包含以下文档的experiments集合:

{ "_id" : 1, "A" : [ "red", "blue" ], "B" : [ "red", "blue" ] }
{ "_id" : 2, "A" : [ "red", "blue" ], "B" : [ "blue", "red", "blue" ] }
{ "_id" : 3, "A" : [ "red", "blue" ], "B" : [ "red", "blue", "green" ] }
{ "_id" : 4, "A" : [ "red", "blue" ], "B" : [ "green", "red" ] }
{ "_id" : 5, "A" : [ "red", "blue" ], "B" : [ ] }
{ "_id" : 6, "A" : [ "red", "blue" ], "B" : [ [ "red" ], [ "blue" ] ] }
{ "_id" : 7, "A" : [ "red", "blue" ], "B" : [ [ "red", "blue" ] ] }
{ "_id" : 8, "A" : [ ], "B" : [ ] }
{ "_id" : 9, "A" : [ ], "B" : [ "red" ] }

以下操作使用$setIsSubset运算符确定A数组是否是B数组的子集:

db.experiments.aggregate(
   [
     { $project: { A:1, B: 1, AisSubset: { $setIsSubset: [ "$A", "$B" ] }, _id:0 } }
   ]
)

该操作返回以下结果:

{ "A" : [ "red", "blue" ], "B" : [ "red", "blue" ], "AisSubset" : true }
{ "A" : [ "red", "blue" ], "B" : [ "blue", "red", "blue" ], "AisSubset" : true }
{ "A" : [ "red", "blue" ], "B" : [ "red", "blue", "green" ], "AisSubset" : true }
{ "A" : [ "red", "blue" ], "B" : [ "green", "red" ], "AisSubset" : false }
{ "A" : [ "red", "blue" ], "B" : [ ], "AisSubset" : false }
{ "A" : [ "red", "blue" ], "B" : [ [ "red" ], [ "blue" ] ], "AisSubset" : false }
{ "A" : [ "red", "blue" ], "B" : [ [ "red", "blue" ] ], "AisSubset" : false }
{ "A" : [ ], "B" : [ ], "AisSubset" : true }
{ "A" : [ ], "B" : [ "red" ], "AisSubset" : true }
首页