当mongo数组具有特定值时，省略它的一部分

{
  "_id": ObjectId("60a5e3c6a6e5a9a7e8b7c6d5"),
  "name": "John",
  "age": 30,
  "hobbies": [
    {
      "name": "reading",
      "level": "high"
    },
    {
      "name": "swimming",
      "level": "medium"
    },
    {
      "name": "running",
      "level": "low"
    }
  ]
}

db.users.find(
  { "hobbies": { "$elemMatch": { "level": "medium" } } },
  { "hobbies.$": 1 }
)

{
  "_id": ObjectId("60a5e3c6a6e5a9a7e8b7c6d5"),
  "hobbies": [
    {
      "name": "reading",
      "level": "high"
    },
    {
      "name": "swimming",
      "level": "medium"
    }
  ]
}