IOS：如何从 Firebase 实时数据库中的列表中获取特定的更改子项？

Question

I have List of objects in firebase DB. how to get specific child who changed in the list? Do I have made connection with every child?

Answer 1

Actually yes you have to do that. If you eg have users in there, you'll end up with something like this:

{
  users: {
    "user-0": {
      "firstName": "Max",
      "lastName": "Powers"
    },
    "user-1": {
      "firstName": "Maxime",
      "lastName": "Powers"
    }
  }
}

Now, from your apps perspective, the user is signed in and therefore the app knows the user-id. With this information you can subscribe to changes on the whole user.

If you go one step further and nest eg rides below each user, as a mobility app will do, you end up with a JSON like this:

{
  users: {
    "user-0": {
      "rides": {
        "ride-0": {
          "updated_at": ...
        }
      }
    }
  }
}

When in this mobility app a user creates a ride, the app will will receive a ride-id from the backend which it can use to subscribe to the related ride in firebase. The path would be eg users/<user-id>/rides/<ride-id> . The app will then get updates each time this ride is updted in the realtime database.

In the end each user has multiple subscriptions. We do it for a couple of years this way and it works quite well