MongoDB聚合运算符：$setEquals

MongoDB聚合运算符：$setEquals

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

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
}