How to exclude an element from a Firestore query?

Question

I have a collection of users and I want to query all users from the database and display them in a RecyclerView except one, mine. This is my db

Answer 1

The simplest solution would be to use a PagedListAdapter and create a custom DataSource for the Firestore queries. In the DataSource the Query can be transformed into an Array or ArrayList in which you can easily remove your item before adding the data to the method callback.onResult(...).

I used a similar solution to process data after a Firestore query in order to filter and sort by a time attribute, and then re-sort by a quality score attribute in the client before passing the data back in to callback.onResult(...).

Documentation

• Google: Build your own data sources
• Codepath: Paging Library Guide

Data Source Sample

class ContentFeedDataSource() : ItemKeyedDataSource() {

override fun loadBefore(params: LoadParams, callback: LoadCallback) {}

override fun getKey(item: Content) = item.timestamp

override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback) {
    FirestoreCollections.contentCollection
            .collection(FirestoreCollections.ALL_COLLECTION)
            .orderBy(Constants.TIMESTAMP, Query.Direction.DESCENDING)
            .whereGreaterThanOrEqualTo(Constants.TIMESTAMP, DateAndTime.getTimeframe(WEEK))
            .limit(params.requestedLoadSize.toLong())
            .get().addOnCompleteListener {
                val items = arrayListOf()
                for (document in it.result.documents) {
                    val content = document.toObject(Content::class.java)
                    items.add(content)
                }
                callback.onResult(items.sortedByDescending { it?.qualityScore })
            }
}

override fun loadAfter(params: LoadParams, callback: LoadCallback) {
    FirestoreCollections.contentCollection
            .collection(FirestoreCollections.ALL_COLLECTION)
            .orderBy(Constants.TIMESTAMP, Query.Direction.DESCENDING)
            .startAt(params.key)
            .whereGreaterThanOrEqualTo(Constants.TIMESTAMP, DateAndTime.getTimeframe(WEEK))
            .limit(params.requestedLoadSize.toLong())
            .get().addOnCompleteListener {
                val items = arrayListOf()
                for (document in it.result.documents) {
                    val content = document.toObject(Content::class.java)
                    items.add(content)
                }
                val sortedByQualityScore = ArrayList(items.sortedByDescending { it?.qualityScore })
                callback.onResult(sortedByQualityScore)
                sortedByQualityScore.clear()
            }
}
}