MongoDB 聚合 $out
聚合 $out
此聚合阶段将聚合管道返回的文档写入一个集合。
The $out stage must be the last stage of the aggregation pipeline. ($out 阶段必须是聚合管道的最后一个阶段。)
示例
In this example, we are using the "sample_airbnb" database loaded from our sample data in the Intro to Aggregations section. (在此示例中，我们使用的是在“聚合入门”部分的示例数据中加载的“sample_airbnb”数据库。)
db.listingsAndReviews.aggregate([
{
$group: {
_id: "$property_type",
properties: {
$push: {
name: "$name",
accommodates: "$accommodates",
price: "$price",
},
},
},
},
{ $out: "properties_by_type" },
])
The first stage will group properties by the property_type and include the name, accommodates, and price fields for each. The $out stage will create a new collection called properties_by_type in the current database and write the resulting documents into that collection. (第一个阶段将按 property_type 对房产进行分组，并为每个房产包含 name、accommodates 和 price 字段。$out 阶段将在当前数据库中创建一个名为 properties_by_type 的新集合，并将结果文档写入该集合。)
