MongoDB - double $group make nested a nested
MongoDB - double $group make nested a nested
提问于 2019-12-26 02:02:49
我有一个集合，它在unwind之后具有这样的结构(我删除了我认为与问题无关的信息)
{
"_id" : ObjectId("1"),
"Members" : {
"City" : "New York"
},
"Group_name" : "Group A"
}
{
"_id" : ObjectId("2"),
"Members" : {
"City" : "Seattle"
},
"Group_name" : "Group A"
}
{
"_id" : ObjectId("3"),
"Members" : {
"City" : "Seattle"
},
"Group_name" : "Group A"
}
{
"_id" : ObjectId("4"),
"Members" : {
"City" : "New York"
},
"Group_name" : "Group B"
}
{
"_id" : ObjectId("5"),
"Members" : {
"City" : "Los Angeles"
},
"Group_name" : "Group B"
}
{
"_id" : ObjectId("6"),
"Members" : {
"City" : "Los Angeles"
},
"Group_name" : "Group B"
}我使用了双对象Id来得到如下结果：
{ "_id" : { "group" : "A", "city" : "New York" }, "totalMembers" : 1 }
{ "_id" : { "group" : "A", "city" : "Seattle" }, "totalMembers" : 2 }
{ "_id" : { "group" : "B", "city" : "New York" }, "totalMembers" : 1 }
{ "_id" : { "group" : "B", "city" : "Los Angeles" }, "totalMembers" : 2 }我希望能够获得一个具有以下结构的文档：
{
"_id" : "A",
"Cities" : {
"New York" : 1,
"Seattle" : 2
}
}
{
"_id" : "B",
"Cities" : {
"New York" : 1,
"Los Angeles" : 2
}
}到目前为止，这是我的代码，我还不能先按“group”分组，然后再按“city”分组。
db.Users_Group.aggregate([
{"$unwind":"$Members"},
{"$group":{"_id":{"group":"$Group_Name","City":"$Members.City"},"totalUsers":{"$sum":1}}},
{"$group":{"_id":"$_id.grupo","total":{"$sum":1}}}
] )这样，我就可以得到该组中所有成员的总和，而不是按城市分隔。如何将各个城市的文档与每个群组中该城市的总用户进行嵌套？感谢大家在这方面的帮助。提前谢谢。
回答 1
Stack Overflow用户
回答已采纳
发布于 2019-12-26 04:23:19
您需要再运行一次$group，并为$arrayToObject准备数据，这需要一组k-v对：
db.collection.aggregate([
// your current aggregation stages
{
$group: {
_id: "$_id.group",
Cities: { $push: { k: "$_id.city", v: "$totalMembers" } }
}
},
{
$project: {
_id: 1,
Cities: { $arrayToObject: "$Cities" }
}
}
])页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/59480786
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