使用MongoDB的多级$ group
要实现多级$group，请使用MongoDB聚合。让我们创建一个包含文档的集合-
> db.demo76.insertOne({ Name:"Chris","Age" : 21, "CountryName" : 'US' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42281")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 21, "CountryName" : 'US' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42282")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 23, "CountryName" : 'UK' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42283")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 23, "CountryName" : 'UK' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42284")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 21, "CountryName" : 'AUS' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42285")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 21, "CountryName" : 'AUS' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42286")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 23, "CountryName" : 'AUS' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42287")
}
> db.demo76.insertOne({ Name:"Chris","Age" : 21, "CountryName" : 'UK' });
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bd3e571bf0181ecc42288")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo76.find();
这将产生以下输出-
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42281"), "Name" : "Chris", "Age" : 21, "CountryName" : "US" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42282"), "Name" : "Chris", "Age" : 21, "CountryName" : "US" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42283"), "Name" : "Chris", "Age" : 23, "CountryName" : "UK" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42284"), "Name" : "Chris", "Age" : 23, "CountryName" : "UK" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42285"), "Name" : "Chris", "Age" : 21, "CountryName" : "AUS" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42286"), "Name" : "Chris", "Age" : 21, "CountryName" : "AUS" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42287"), "Name" : "Chris", "Age" : 23, "CountryName" : "AUS" }
{ "_id" : ObjectId("5e2bd3e571bf0181ecc42288"), "Name" : "Chris", "Age" : 21, "CountryName" : "UK" }以下是实现多级$group的查询-
> db.demo76.aggregate([
... { "$match": { "Name": "Chris" }},
... { "$group": {
... "_id": { "Age": "$Age", "CountryName": "$CountryName" },
... "count": { "$sum": 1 }
... }},
... { "$group": {
... "_id": "$_id.Age",
... "CountryName": {
... "$push": {
... "k": "$_id.CountryName",
... "v": "$count"
... }
... }
... }},
... { "$addFields": {
... "CountryName": {
... "$arrayToObject": "$CountryName"
... }
... }}
... ]);这将产生以下输出-
{ "_id" : 23, "CountryName" : { "AUS" : 1, "UK" : 2 } }
{ "_id" : 21, "CountryName" : { "UK" : 1, "AUS" : 2, "US" : 2 } }