Question

有Post收集数据。

{"_id" : 1
,"subject" : "post1"
,"usersLiking": [
  {"user_id" : "user_id_01", "username" : "user01"}
  {"user_id" : "user_id_02", "username" : "user02"}
 ]
,"usersDisliking": [
  {"user_id" : "user_id_03", "username" : "user03"}
  {"user_id" : "user_id_04", "username" : "user04"}
  {"user_id" : "user_id_05", "username" : "user05"}
 ]
}
,{"_id" : 2
,"subject" : "post2"
,"usersLiking": [
  {"user_id" : "user_id_01", "username" : "user01"}
 ]
,"usersDisliking": [
  {"user_id" : "user_id_03", "username" : "user03"}
  {"user_id" : "user_id_04", "username" : "user04"}
 ]
}

我希望输出如下。

{"_id" : 1, "usersLikingCount" : 2, "usersDislikingCount" : 3}
{"_id" : 2, "usersLikingCount" : 1, "usersDislikingCount" : 2}

这对我来说太复杂了。我想得到多个嵌入文档的数量。查询是什么？感谢。

Answer 1

试试这个

db.collectionName.aggregate({"$project":{"usersLikingCount":{"$size":"$usersLiking"},"usersDislikingCount":{"$size":"$usersDisliking"}}})

如何在mongoDB上使用聚合

1 个答案: