How does mongodb query a single subdocument

  mongodb, question

db.users.find()
{
_id : ObjectId(5a7d12871541ff3ed0bb9c79) ,
users: [{“id”: 1, “name”:”user1″}, {“id”: 2, “name”: “user2”}]
}

Does mongodb support direct query of subdocuments?

db.users.find({ “user.id” : 1 })
{
_id : ObjectId(5a7d12871541ff3ed0bb9c79) ,
users: [{“id”: 1, “name”:”user1″}, {“id”: 2, “name”: “user2”}]
}

This is the document, but I want to get {id:1,name:user1}, how should this statement be written?

If it can be determined that only one array element meets the requirements, the simplest way to write it is:

rs0:PRIMARY> db.users.find({ "users.id" : 1 }, {"users.$.id": 1})
 { "_id" : ObjectId("5a7d12871541ff3ed0bb9c79"), "users" : [ { "id" : 1, "name" : "user1" } ] }

If not, then$Only the first element satisfying the condition will be returned. To want all the elements, you need aggregation:

db.users.aggregate([
 {$match: {"users.id": 1}},
 {
 $project: {
 users: {
 $filter: {
 input: "$users",
 as: "user",
 cond: {
 $eq: ["$$user.id", 1]
 }
 }
 }
 }
 }
 ]);

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