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fix(database): fix DatabasePagingSource pagination when using orderByChild #2336

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Merged
demolaf merged 4 commits into from
Jun 19, 2026
Merged

fix(database): fix DatabasePagingSource pagination when using orderByChild #2336

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66db2bd
fix(database): fix DatabasePagingSource pagination when using orderBy…
demolaf Jun 17, 2026
5df651d
fix(database): make DatabasePagingKey public and add equals/hashCode
demolaf Jun 17, 2026
a9e554b
fix(database): surface load errors to logcat and fix lifecycle observ…
demolaf Jun 17, 2026
bbd4687
fix(database): extend orderByValue() cursor support and use shared Te…
demolaf Jun 19, 2026
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104 changes: 104 additions & 0 deletions database/src/androidTest/java/com/firebase/ui/database/paging/DatabasePagingSourceTest.java
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@@ -0,0 +1,104 @@
package com.firebase.ui.database.paging;

import androidx.paging.PagingSource;
import androidx.test.core.app.ApplicationProvider;
import androidx.test.ext.junit.runners.AndroidJUnit4;

import com.firebase.ui.database.Bean;
import com.firebase.ui.database.TestUtils;
import com.google.firebase.FirebaseApp;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

import androidx.annotation.NonNull;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

@RunWith(AndroidJUnit4.class)
public class DatabasePagingSourceTest {
private static final int PAGE_SIZE = 3;
private static final int TOTAL_ITEMS = 6;

private DatabaseReference mRef;

@Before
public void setUp() throws InterruptedException {
FirebaseApp app = TestUtils.getAppInstance(ApplicationProvider.getApplicationContext());
mRef = FirebaseDatabase.getInstance(app).getReference().child("paging_test");

mRef.removeValue();
for (int i = 1; i <= TOTAL_ITEMS; i++) {
mRef.push().setValue(new Bean(i));
}

CountDownLatch latch = new CountDownLatch(1);
mRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
if (snapshot.getChildrenCount() >= TOTAL_ITEMS) {
mRef.removeEventListener(this);
latch.countDown();
}
}

@Override
public void onCancelled(@NonNull DatabaseError error) {}
});
assertTrue("Timed out seeding test data", latch.await(30, TimeUnit.SECONDS));
}

@After
public void tearDown() {
mRef.removeValue();
}

@Test
public void testOrderByChild_noDuplicatesAcrossPages() {
DatabasePagingSource source = new DatabasePagingSource(mRef.orderByChild("number"));

PagingSource.LoadResult<DatabasePagingKey, DataSnapshot> result1 =
source.loadSingle(new PagingSource.LoadParams.Refresh<>(null, PAGE_SIZE, false))
.timeout(30, TimeUnit.SECONDS)
.blockingGet();

assertTrue(result1 instanceof PagingSource.LoadResult.Page);
PagingSource.LoadResult.Page<DatabasePagingKey, DataSnapshot> page1 =
(PagingSource.LoadResult.Page<DatabasePagingKey, DataSnapshot>) result1;
assertEquals(PAGE_SIZE, page1.getData().size());

DatabasePagingKey nextKey = page1.getNextKey();

PagingSource.LoadResult<DatabasePagingKey, DataSnapshot> result2 =
source.loadSingle(new PagingSource.LoadParams.Append<>(nextKey, PAGE_SIZE, false))
.timeout(30, TimeUnit.SECONDS)
.blockingGet();

assertTrue(result2 instanceof PagingSource.LoadResult.Page);
PagingSource.LoadResult.Page<DatabasePagingKey, DataSnapshot> page2 =
(PagingSource.LoadResult.Page<DatabasePagingKey, DataSnapshot>) result2;

Set<String> allKeys = new HashSet<>();
for (DataSnapshot snapshot : page1.getData()) {
allKeys.add(snapshot.getKey());
}
for (DataSnapshot snapshot : page2.getData()) {
assertTrue("Duplicate key across pages: " + snapshot.getKey(),
allKeys.add(snapshot.getKey()));
}
assertEquals(TOTAL_ITEMS, allKeys.size());
}
}
35 changes: 35 additions & 0 deletions database/src/main/java/com/firebase/ui/database/paging/DatabasePagingKey.java
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@@ -0,0 +1,35 @@
package com.firebase.ui.database.paging;

import java.util.Objects;

public class DatabasePagingKey {
private final Object mChildValue;
private final String mNodeKey;

public DatabasePagingKey(Object childValue, String nodeKey) {
mChildValue = childValue;
mNodeKey = nodeKey;
}

public Object getChildValue() {
return mChildValue;
}

public String getNodeKey() {
return mNodeKey;
}

@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
DatabasePagingKey that = (DatabasePagingKey) o;
return Objects.equals(mChildValue, that.mChildValue) &&
Objects.equals(mNodeKey, that.mNodeKey);
}

@Override
public int hashCode() {
return Objects.hash(mChildValue, mNodeKey);
}
}
2 changes: 1 addition & 1 deletion database/src/main/java/com/firebase/ui/database/paging/DatabasePagingOptions.java
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Expand Up @@ -94,7 +94,7 @@ public Builder<T> setQuery(@NonNull Query query,
public Builder<T> setQuery(@NonNull Query query,
@NonNull PagingConfig config,
@NotNull SnapshotParser<T> parser) {
final Pager<String, DataSnapshot> pager = new Pager<>(config,
final Pager<DatabasePagingKey, DataSnapshot> pager = new Pager<>(config,
() -> new DatabasePagingSource(query));
mData = PagingLiveData.cachedIn(PagingLiveData.getLiveData(pager),
mOwner.getLifecycle());
Expand Down
90 changes: 63 additions & 27 deletions database/src/main/java/com/firebase/ui/database/paging/DatabasePagingSource.java
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@@ -1,12 +1,16 @@
package com.firebase.ui.database.paging;

import android.annotation.SuppressLint;
import android.util.Log;

import com.google.android.gms.tasks.Task;
import com.google.android.gms.tasks.Tasks;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.Query;
import com.google.firebase.database.snapshot.Index;
import com.google.firebase.database.snapshot.PathIndex;
import com.google.firebase.database.snapshot.ValueIndex;

import org.jetbrains.annotations.Nullable;

Expand All @@ -21,7 +25,7 @@
import io.reactivex.rxjava3.core.Single;
import io.reactivex.rxjava3.schedulers.Schedulers;

public class DatabasePagingSource extends RxPagingSource<String, DataSnapshot> {
public class DatabasePagingSource extends RxPagingSource<DatabasePagingKey, DataSnapshot> {
private final Query mQuery;

private static final String STATUS_DATABASE_NOT_FOUND = "DATA_NOT_FOUND";
Expand All @@ -32,29 +36,42 @@ public DatabasePagingSource(Query query) {
this.mQuery = query;
}

private static final String TAG = "DatabasePagingSource";

/**
* DatabaseError.fromStatus() is not meant to be public.
* DatabaseError.fromStatus() and PathIndex are not meant to be public.
*/
@SuppressLint("RestrictedApi")
@NonNull
@Override
public Single<LoadResult<String, DataSnapshot>> loadSingle(@NonNull LoadParams<String> params) {
public Single<LoadResult<DatabasePagingKey, DataSnapshot>> loadSingle(
@NonNull LoadParams<DatabasePagingKey> params) {
final Index index = mQuery.getSpec().getIndex();
final boolean needsIndexedCursor =
index instanceof PathIndex || index instanceof ValueIndex;
Task<DataSnapshot> task;

if (params.getKey() == null) {
task = mQuery.limitToFirst(params.getLoadSize()).get();
} else {
task = mQuery.startAt(null, params.getKey()).limitToFirst(params.getLoadSize() + 1).get();
DatabasePagingKey key = params.getKey();
if (needsIndexedCursor) {
task = startAtChildValue(key.getChildValue(), key.getNodeKey())
.limitToFirst(params.getLoadSize() + 1).get();
} else {
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// orderByKey() — the node key alone is a sufficient cursor
task = mQuery.startAt(null, key.getNodeKey())
.limitToFirst(params.getLoadSize() + 1).get();
}
}

return Single.fromCallable(() -> {
try {
Tasks.await(task);
DataSnapshot dataSnapshot = task.getResult();
if (dataSnapshot.exists()) {

//Make List of DataSnapshot
List<DataSnapshot> data = new ArrayList<>();
String lastKey = null;
DatabasePagingKey lastKey = null;

if (params.getKey() == null) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Expand All @@ -69,15 +86,16 @@ public Single<LoadResult<String, DataSnapshot>> loadSingle(@NonNull LoadParams<S
}

while (iterator.hasNext()) {
DataSnapshot snapshot = iterator.next();
data.add(snapshot);
data.add(iterator.next());
}
}

//Detect End of Data
if (!data.isEmpty()) {
//Get Last Key
lastKey = getLastPageKey(data);
DataSnapshot last = data.get(data.size() - 1);
Object cursorValue = needsIndexedCursor
? getIndexedValue(last, index) : null;
lastKey = new DatabasePagingKey(cursorValue, last.getKey());
}
return toLoadResult(data, lastKey);
} else {
Expand All @@ -89,19 +107,45 @@ public Single<LoadResult<String, DataSnapshot>> loadSingle(@NonNull LoadParams<S
}
} catch (ExecutionException e) {
if (e.getCause() instanceof Exception) {
// throw the original Exception
throw (Exception) e.getCause();
}
// Only throw a new Exception when the original
// Throwable cannot be cast to Exception
throw new Exception(e);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
return new LoadResult.Error<DatabasePagingKey, DataSnapshot>(e);
}
}).subscribeOn(Schedulers.io()).onErrorReturn(LoadResult.Error::new);
}).subscribeOn(Schedulers.io()).onErrorReturn(e -> {
Log.e(TAG, "DatabasePagingSource load failed", e);
return new LoadResult.Error<>(e);
});
}

@SuppressLint("RestrictedApi")
private Object getIndexedValue(DataSnapshot snapshot, Index index) {
if (index instanceof PathIndex) {
return snapshot.child(((PathIndex) index).getQueryDefinition()).getValue();
} else if (index instanceof ValueIndex) {
return snapshot.getValue();
}
return null;
}

private LoadResult<String, DataSnapshot> toLoadResult(
@SuppressLint("RestrictedApi")
private Query startAtChildValue(Object childValue, String nodeKey) {
if (childValue instanceof String) {
return mQuery.startAt((String) childValue, nodeKey);
} else if (childValue instanceof Boolean) {
return mQuery.startAt((Boolean) childValue, nodeKey);
} else if (childValue instanceof Number) {
return mQuery.startAt(((Number) childValue).doubleValue(), nodeKey);
}
// childValue is null when a node lacks the ordered child field; key alone keeps the cursor correct
return mQuery.startAt(null, nodeKey);
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}
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private LoadResult<DatabasePagingKey, DataSnapshot> toLoadResult(
@NonNull List<DataSnapshot> snapshots,
String nextPage
DatabasePagingKey nextPage
) {
return new LoadResult.Page<>(
snapshots,
Expand All @@ -111,18 +155,10 @@ private LoadResult<String, DataSnapshot> toLoadResult(
LoadResult.Page.COUNT_UNDEFINED);
}

@Nullable
private String getLastPageKey(@NonNull List<DataSnapshot> data) {
if (data.isEmpty()) {
return null;
} else {
return data.get(data.size() - 1).getKey();
}
}

@Nullable
@Override
public String getRefreshKey(@NonNull PagingState<String, DataSnapshot> state) {
public DatabasePagingKey getRefreshKey(
@NonNull PagingState<DatabasePagingKey, DataSnapshot> state) {
return null;
}
}
17 changes: 12 additions & 5 deletions database/src/main/java/com/firebase/ui/database/paging/FirebaseRecyclerPagingAdapter.java
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Expand Up @@ -7,10 +7,10 @@
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.LifecycleEventObserver;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.OnLifecycleEvent;
import androidx.paging.PagingData;
import androidx.paging.PagingDataAdapter;
import androidx.recyclerview.widget.RecyclerView;
Expand All @@ -22,7 +22,7 @@
*/
public abstract class FirebaseRecyclerPagingAdapter<T, VH extends RecyclerView.ViewHolder>
extends PagingDataAdapter<DataSnapshot, VH>
implements LifecycleObserver {
implements LifecycleEventObserver {

private DatabasePagingOptions<T> mOptions;
private SnapshotParser<T> mParser;
Expand Down Expand Up @@ -88,7 +88,6 @@ public void updateOptions(@NonNull DatabasePagingOptions<T> options) {
/**
* Start listening to paging / scrolling events and populating adapter data.
*/
@OnLifecycleEvent(Lifecycle.Event.ON_START)
public void startListening() {
mPagingData.observeForever(mDataObserver);
}
Expand All @@ -97,11 +96,19 @@ public void startListening() {
* Unsubscribe from paging / scrolling events, no more data will be populated, but the existing
* data will remain.
*/
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
public void stopListening() {
mPagingData.removeObserver(mDataObserver);
}

@Override
public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Lifecycle.Event event) {
if (event == Lifecycle.Event.ON_START) {
startListening();
} else if (event == Lifecycle.Event.ON_STOP) {
stopListening();
}
}

@Override
public void onBindViewHolder(@NonNull VH viewHolder, int position) {
DataSnapshot snapshot = getItem(position);
Expand Down
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