Kotlin 具有多个不同类型来源的 LiveData

我目前有一个包含MyItem个列表的项目，使用Firebase/LiveData.它被分成几个小组，每个小组都有项目.

如果发生以下任何情况，我希望能够更新此列表:

1. An item is updated (on the backend through Firebase)
2. A filter is changed (a separate table on Firebase for each user)
3. An item is bookmarked (a separate table on Firebase for each user)

To get the list of contents, I have a function like this to return LiveData that will update whenever an item is updated (#1).

database

getList(id: String): LiveData<List<MyItem>> {
    val data = MutableLiveData<List<MyItem>>()

    firestore
        .collection("groups")
        .document(id)
        .collection("items")
            .addSnapshotListener { snapshot, exception ->
                val items = snapshot?.toObjects(MyItem::class.java) ?: emptyList()

                // filter items 

                data.postValue(items)
        }

    return data
}

And within my ViewModel, I have logic for handling that case.

viewmodel

private val result = MediatorLiveData<Resource<List<MyItem>>>()

private var source: LiveData<List<MyItem>>? = null
val contents: LiveData<Resource<List<MyItem>>>
    get() {
        val group = database.group

        // if the selected group is changed.
        return Transformations.switchMap(group) { id ->
            // showing loading indicator
            result.value = Resource.loading(null)

            if (id != null) {
                // only 1 source for the current group
                source?.let {
                    result.removeSource(it)
                }

                source = database.getList(id).also {
                    result.addSource(it) {
                        result.value = Resource.success(it)
                    }
                }

                // how to add in source of filter changes?

            } else {
                result.value = Resource.init(null)
            }
            return@switchMap result
        }
    }

The logic is pretty complex, and hard to follow. Is there a better way to structure this to handle multiple different changes? What's the best way to store the user's current filters?

谢谢.