MongoDB聚合运算符：$setEquals
文章目录
$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
}