$anyElementTrue (aggregation)
定义
$anyElementTrue
Evaluates an array as a set and returns
true
if any of the elements aretrue
andfalse
otherwise. An empty array returnsfalse
.$anyElementTrue
采用以下语法:{ $anyElementTrue: [ <expression> ] } <expression>
本身必须解析为一个数组,与表示参数列表的外部数组分开。 有关表达式的更多信息,请参阅表达式操作符。
行为
如果集合包含嵌套数组元素,$anyElementTrue
不会下降进入嵌套数组,而是在顶层计算数组。
除了 false
布尔值外,$anyElementTrue
还将以下值计算为 false
:null
、0
和 undefined
值。$anyElementTrue
将所有其他值(包括非零数值和数组)计算为 true
。
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例子
使用以下文档创建名为survey
的示例collection:
db.survey.insertMany([ { "_id" : 1, "responses" : [ true ] }, { "_id" : 2, "responses" : [ true, false ] }, { "_id" : 3, "responses" : [ ] }, { "_id" : 4, "responses" : [ 1, true, "seven" ] }, { "_id" : 5, "responses" : [ 0 ] }, { "_id" : 6, "responses" : [ [ ] ] }, { "_id" : 7, "responses" : [ [ 0 ] ] }, { "_id" : 8, "responses" : [ [ false ] ] }, { "_id" : 9, "responses" : [ null ] }, { "_id" : 10, "responses" : [ undefined ] } ])
The following operation uses the $anyElementTrue
operator
to determine if the responses
array contains any value that
evaluates to true
:
db.survey.aggregate( [ { $project: { responses: 1, isAnyTrue: { $anyElementTrue: [ "$responses" ] }, _id: 0 } } ] )
操作返回以下结果:
{ "responses" : [ true ], "isAnyTrue" : true } { "responses" : [ true, false ], "isAnyTrue" : true } { "responses" : [ ], "isAnyTrue" : false } { "responses" : [ 1, true, "seven" ], "isAnyTrue" : true } { "responses" : [ 0 ], "isAnyTrue" : false } { "responses" : [ [ ] ], "isAnyTrue" : true } { "responses" : [ [ 0 ] ], "isAnyTrue" : true } { "responses" : [ [ false ] ], "isAnyTrue" : true } { "responses" : [ null ], "isAnyTrue" : false } { "responses" : [ undefined ], "isAnyTrue" : false }