$anyElementTrue (aggregation)

Definition定义

$anyElementTrue

Evaluates an array as a set and returns true if any of the elements are true and false otherwise. An empty array returns false.将数组计算为集合，如果任何元素为true，则返回true，否则返回false。空数组返回false。

$anyElementTrue has the following syntax:具有以下语法：

{ $anyElementTrue: [ <expression> ] }

The <expression> itself must resolve to an array, separate from the outer array that denotes the argument list. <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离。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

If a set contains a nested array element, $anyElementTrue does not descend into the nested array but evaluates the array at top-level.如果集合包含嵌套数组元素，$anyElementTrue不会下降到嵌套数组中，而是在顶级计算数组。

In addition to the false boolean value, $anyElementTrue evaluates as false the following: null, 0, and undefined values. 除了false布尔值外，$anyElementTrue还将以下值计算为false：null、0和undefined的值。The $anyElementTrue evaluates all other values as true, including non-zero numeric values and arrays.$anyElementTrue将所有其他值计算为true，包括非零数值和数组。

Example实例

Create an example collection named survey with the following documents:使用以下文档创建一个名为survey的示例集合：

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 $anyElementTrue operator to determine if the responses array contains any value that evaluates to true:以下操作使用$anyElementTrue运算符来确定responses数组是否包含任何计算结果为true的值：

db.survey.aggregate(
   [
     { $project: { responses: 1, isAnyTrue: { $anyElementTrue: [ "$responses" ] }, _id: 0 } }
   ]
)

The operation returns the following results:该操作返回以下结果：

{ "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 }