MongoDB聚合运算符：$setEquals

$setEquals聚合运算符用于比较两个或多个数组，如果它们有相同的不重复的元素，则返回true，否则返回false。

语法

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

字段说明：

参数可以是任何可以解析为数组的表达式即可。

使用

$setEquals对数组执行集合操作，将数组视为集合。如果数组包含重复元素，$setEquals会忽略重复元素，并且$setEquals也会忽略元素的顺序。

如果集合包含嵌套数组元素，$setEquals 不会进入嵌套数组，而对顶层对数组进行评估。

举例	结果
{ $setEquals: [ [ "a", "b", "a" ], [ "b", "a" ] ] }	true
{ $setEquals: [ [ "a", "b" ], [ [ "a", "b" ] ] ] }	false

举例

使用下面的脚本创建bakeryOrders集合：

db.bakeryOrders.insertMany( [{ _id: 0, cakes: ["chocolate", "vanilla"], cupcakes: ["chocolate", "vanilla"] },{ _id: 1, cakes: ["chocolate", "vanilla"], cupcakes: ["vanilla", "chocolate"] },{ _id: 2, cakes: ["chocolate", "chocolate"], cupcakes: ["chocolate"] },{ _id: 3, cakes: ["vanilla"], cupcakes: ["chocolate"] },{ _id: 4, cakes: ["vanilla"], cupcakes: [] }
] )

以下操作使用$setEquals运算符来确定每个订单中的cakes数组和 cupcakes数组是否包含相同的口味：：

db.bakeryOrders.aggregate([{$project: {_id: 0,cakes: 1,cupcakes: 1,sameFlavors: { $setEquals: [ "$cakes", "$cupcakes" ] }}}] )

操作返回下面的结果：

{cakes: [ "chocolate", "vanilla" ],cupcakes: [ "chocolate", "vanilla" ],sameFlavors: true
},
{cakes: [ "chocolate", "vanilla" ],cupcakes: [ "vanilla", "chocolate" ],sameFlavors: true
},
{cakes: [ "chocolate", "chocolate" ],cupcakes: [ "chocolate" ],sameFlavors: true
},
{cakes: [ "vanilla" ],cupcakes: [ "chocolate" ],sameFlavors: false
},
{cakes: [ "vanilla" ],cupcakes: [],sameFlavors: false
}