汇总：将日期嵌套在嵌套文档（嵌套对象）中并显示计数？
对于聚合，请aggregate()在MongoDB中使用。用$组将日期分组。让我们创建一个包含文档的集合-
> db.demo717.insertOne(
... {
... "shippingdetails":
... [
... {
... duedate:"2020-04-29 22:33:04",
... },
... {
... duedate:"2020-03-29 22:33:04",
... },
... {
... duedate:"2020-04-29 22:33:04",
... },
... {
... duedate:"2020-01-29 22:33:04",
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea9b3cd85324c2c98cc4c30")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo717.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5ea9b3cd85324c2c98cc4c30"),
"shippingdetails" : [
{
"duedate" : "2020-04-29 22:33:04"
},
{
"duedate" : "2020-03-29 22:33:04"
},
{
"duedate" : "2020-04-29 22:33:04"
},
{
"duedate" : "2020-01-29 22:33:04"
}
]
}以下是查询聚合以将嵌套文档（嵌套对象）中的日期分组-
> db.demo717.aggregate(
... {
... $unwind:"$shippingdetails"},
... {
... $group: {
... _id: "$shippingdetails.duedate",
... count: {
... $sum: 1
... }
... }
... }
... )这将产生以下输出-
{ "_id" : "2020-01-29 22:33:04", "count" : 1 }
{ "_id" : "2020-03-29 22:33:04", "count" : 1 }
{ "_id" : "2020-04-29 22:33:04", "count" : 2 }