MongoDB将带有数组的记录转换为新集合中的多个记录
为此，可以将$out与aggregate()和$undend一起使用。让我们用文档创建一个集合
> db.demo757.insertOne(
... {
... "id": 101,
... "Name": ["John", "Bob", "Chris"]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eb025745637cd592b2a4ae2")
}
> db.demo757.insertOne(
... {
... "id": 102,
... "Name": ["David"]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eb025755637cd592b2a4ae3")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo757.find();
这将产生以下输出-
{ "_id" : ObjectId("5eb025745637cd592b2a4ae2"), "id" : 101, "Name" : [ "John", "Bob", "Chris" ] }
{ "_id" : ObjectId("5eb025755637cd592b2a4ae3"), "id" : 102, "Name" : [ "David" ] }以下是将具有数组的一个记录转换为新集合中的多个记录的查询-
> db.demo757.aggregate([
... {$unwind: '$Name'},
... {$project: {_id: 0}},
... {$out: 'demo758'}
... ])
> db.demo758.find();这将产生以下输出-
{ "_id" : ObjectId("5eb02582192bedc4738b5881"), "id" : 101, "Name" : "John" }
{ "_id" : ObjectId("5eb02582192bedc4738b5882"), "id" : 101, "Name" : "Bob" }
{ "_id" : ObjectId("5eb02582192bedc4738b5883"), "id" : 101, "Name" : "Chris" }
{ "_id" : ObjectId("5eb02582192bedc4738b5884"), "id" : 102, "Name" : "David" }