Firestore Pagination : StartAfter query with DocumentSnapshot not working

Question

I have a list of offers/deals saved in my firestore database. I want to fetch the first 3 deals sorted by discount in desc order i.e the deals with highest discount comes first and then next highest and so on. I am fetching them in segments of 3.

I am trying to achieve the same using android code. So, that the first 3 elements with discount 55,44,28 should come first, later 27,27,21 and finally 19,4.

class ContentGenerationActivityV1 : AppCompatActivity() {

     var lastDocument : DocumentSnapshot?= null
     lateinit var filterQuery: Query

     override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_content_generation)

        val doc = FirebaseFirestore.getInstance().collection("steal-deals").document("deals")

       filterQuery = doc.collection(getTodayTimeStamp().toString())
        .orderBy("discount", Query.Direction.DESCENDING)

       filterFetchButton.setOnClickListener {
           if(lastDocument == null){
              fetchFirstFew()
           } else {
            fetchMore()
        }
    }
}

//Get first 3 elements
fun fetchFirstFew(){

    Log.d("N/W CALL ::", "FIRST")

    filterQuery.limit(3) .get()
        .addOnSuccessListener { result ->

            lastDocument = result.documents.last()

            for (document in result) {
                Log.d("DEAL :: ", "${document.id} => ${document.data}")
            }

        }


}

//Get the next 3 elements
fun fetchMore(){

    Log.d("N/W CALL ::", "SECOND")

    filterQuery.startAfter(lastDocument)
        .limit(3).get()
        .addOnSuccessListener { result ->

            lastDocument = result.documents.last()

            for (document in result) {
                Log.d("DEAL :: ", "${document.id} => ${document.data}")
            }


        }
}

But it is always returning the first three elements (55,44,28) no matter what.

Please guide me so in achieving the same.

Check **[this](https://stackoverflow.com/questions/50741958/how-to-paginate-firestore-with-android)** out. Is in Java but I think you'll understand. It's a straightforward example. — Alex Mamo, Sep 14 '19 at 10:05
The code looks fine at first glance. You might want to set a breakpoint in `fetchMore` and run it in a debugger, to see if `lastDocument` has the correct value. — Frank van Puffelen, Sep 14 '19 at 14:22
I checked the `lastDocument` value twice and the i can confirm that the value was correct. — Saurabh Padwekar, Sep 14 '19 at 18:48
Did you find a solution for it yet? I'm having the same problem — Leonardo Dias, Dec 27 '19 at 23:08

score 2 · Answer 1 · answered Jun 25 '20 at 10:58

2

I had the same problem but after some research found out the "startAfter(lastDocument)" returns a new Query instance which you need to get and on that you need to call limit.

val query = filterQuery.startAfter(lastDocument)
query.limit(3).get().addOnSuccessListener {}

answered Jun 25 '20 at 10:58

Ishaan

3,658
2
23
39

Thanks a lot, I thought startAfter was mutating the existing one – user1336321 Mar 26 '21 at 20:04

score 1 · Answer 2 · answered Mar 15 '22 at 10:28

In addition to storing query object in separate reference, you also need to make sure that you are passing the non-null lastDocument to startAfter. You can either cast it to as Document Snapshot or put !! at the variable end

filterQuery.startAfter(lastDocument!!)
    .limit(3).get()

OR

filterQuery.startAfter(lastDocument as DocumentSnapshot)
    .limit(3).get()

It will surely work

score 0 · Answer 3 · edited Apr 27 '21 at 03:41

i just got this issue.

reference

so, in your code

Wrong:

filterQuery.limit(3) .get()
        .addOnSuccessListener { result ->

            lastDocument = result.documents.last()

            for (document in result) {
                Log.d("DEAL :: ", "${document.id} => ${document.data}")
            }

        }

True:

filterQuery = filterQuery.limit(3) .get()
        .addOnSuccessListener { result ->

            lastDocument = result.documents.last()

            for (document in result) {
                Log.d("DEAL :: ", "${document.id} => ${document.data}")
            }

        }

because when you chaining to query, it creates and returns a new Query that starts after the provided document (exclusive). so you have to reassign it!

Firestore Pagination : StartAfter query with DocumentSnapshot not working

3 Answers3