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JAVA-2673 #1950

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c79bc72
JAVA-2673
Apr 29, 2026
71e84a5
remove unused import
Apr 29, 2026
2f1a517
address copilot feedback
Apr 29, 2026
fa700ae
update the docs
Apr 29, 2026
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55 changes: 55 additions & 0 deletions driver-core/src/main/com/mongodb/internal/operation/AsyncWriteThenReadOperationCursor.java
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@@ -0,0 +1,55 @@
/*
* Copyright 2008-present MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.mongodb.internal.operation;

import com.mongodb.MongoNamespace;
import com.mongodb.internal.async.AsyncBatchCursor;
import com.mongodb.internal.async.SingleResultCallback;
import com.mongodb.internal.binding.AsyncReadWriteBinding;
import com.mongodb.internal.connection.OperationContext;

/**
* An async-only operation that performs a write followed by a read that returns a cursor.
*
* <p>Unlike {@link ReadOperationCursor}, this operation requires an {@link AsyncReadWriteBinding}
* so that both the write and the read portions can be executed without narrowing casts.
*
* <p>This class is not part of the public API and may be removed or changed at any time</p>
*/
public interface AsyncWriteThenReadOperationCursor<T> {
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@strogiyotec strogiyotec Apr 29, 2026

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this is a new interface that will be used by OperationExecutorImpl
It adds a new override to execute that accepts this interface instead of ReadOperation
All methods here were copied from ReadOperation interface


/**
* @return the command name of the write phase of this operation (e.g. "mapReduce", "aggregate")
*/
String getCommandName();

/**
* @return the namespace the write phase targets
*/
MongoNamespace getNamespace();

/**
* Executes the write phase followed by the read phase, yielding an {@link AsyncBatchCursor}
* over the results of the read.
*
* @param binding the read-write binding used by both phases
* @param operationContext the operation context to use
* @param callback receives the {@link AsyncBatchCursor} on success, or the failure of either phase
*/
void executeAsync(AsyncReadWriteBinding binding, OperationContext operationContext,
SingleResultCallback<AsyncBatchCursor<T>> callback);
}
3 changes: 2 additions & 1 deletion ...eams/src/main/com/mongodb/reactivestreams/client/internal/ClientSessionPublisherImpl.java
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Expand Up @@ -27,6 +27,7 @@
import com.mongodb.internal.observability.micrometer.TracingManager;
import com.mongodb.internal.observability.micrometer.TransactionSpan;
import com.mongodb.internal.operation.AbortTransactionOperation;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.CommitTransactionOperation;
import com.mongodb.internal.operation.ReadOperation;
import com.mongodb.internal.operation.WriteConcernHelper;
Expand Down Expand Up @@ -88,7 +89,7 @@ public boolean notifyMessageSent() {

@Override
public void notifyOperationInitiated(final Object operation) {
assertTrue(operation instanceof ReadOperation || operation instanceof WriteOperation);
assertTrue(operation instanceof ReadOperation || operation instanceof WriteOperation || operation instanceof AsyncWriteThenReadOperationCursor);
if (!(hasActiveTransaction() || operation instanceof CommitTransactionOperation)) {
assertTrue(getPinnedServerAddress() == null
|| (transactionState != TransactionState.ABORTED && transactionState != TransactionState.NONE));
Expand Down
43 changes: 40 additions & 3 deletions ...-streams/src/main/com/mongodb/reactivestreams/client/internal/MapReducePublisherImpl.java
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Expand Up @@ -40,6 +40,7 @@
import org.bson.BsonDocument;
import org.bson.conversions.Bson;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Mono;

import java.util.concurrent.TimeUnit;
import java.util.function.Function;
Expand Down Expand Up @@ -201,10 +202,46 @@ public ReadOperationCursor<T> asReadOperation(final int initialBatchSize) {
if (inline) {
// initialBatchSize is ignored for map reduce operations.
return createMapReduceInlineOperation();
} else {
return new VoidWriteOperationThenCursorReadOperation<>(createMapReduceToCollectionOperation(),
createFindOperation(initialBatchSize));
}
throw new IllegalStateException("Non-inline map-reduce uses the write-then-read path; "
+ "asReadOperation must not be called.");
}

@Override
public Mono<BatchCursor<T>> batchCursor(final int initialBatchSize) {
if (inline) {
return super.batchCursor(initialBatchSize);
}
return writeThenReadBatchCursor(initialBatchSize);
}
Comment on lines +211 to +216
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@strogiyotec strogiyotec Apr 29, 2026

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Added a unit test here


@Override
public Publisher<T> first() {
if (inline) {
return super.first();
}
return writeThenReadBatchCursor(1)
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@strogiyotec strogiyotec Apr 30, 2026

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this number 1 comes from BatchCursorPublisher

.flatMap(batchCursor -> {
batchCursor.setBatchSize(1);
return Mono.from(batchCursor.next())
.doOnTerminate(batchCursor::close)
.flatMap(results -> {
if (results == null || results.isEmpty()) {
return Mono.empty();
}
return Mono.fromCallable(() -> results.get(0));
});
});
}

private Mono<BatchCursor<T>> writeThenReadBatchCursor(final int initialBatchSize) {
return getMongoOperationPublisher()
.createWriteThenReadOperationMono(
operations -> operations.createTimeoutSettings(maxTimeMS),
() -> new VoidWriteOperationThenCursorReadOperation<>(createMapReduceToCollectionOperation(),
createFindOperation(initialBatchSize)),
getClientSession())
.map(BatchCursor::new);
}

private WrappedMapReduceReadOperation<T> createMapReduceInlineOperation() {
Expand Down
11 changes: 11 additions & 0 deletions ...streams/src/main/com/mongodb/reactivestreams/client/internal/MongoOperationPublisher.java
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Expand Up @@ -60,6 +60,8 @@
import com.mongodb.internal.TimeoutSettings;
import com.mongodb.internal.async.SingleResultCallback;
import com.mongodb.internal.bulk.WriteRequest;
import com.mongodb.internal.async.AsyncBatchCursor;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.IndexHelper;
import com.mongodb.internal.operation.Operations;
import com.mongodb.internal.operation.ReadOperation;
Expand Down Expand Up @@ -513,6 +515,15 @@ <T> Mono<T> createReadOperationMono(final Supplier<TimeoutSettings> timeoutSetti
.execute(readOperation, readPreference, getReadConcern(), clientSession);
}

<R> Mono<AsyncBatchCursor<R>> createWriteThenReadOperationMono(
final Function<Operations<?>, TimeoutSettings> timeoutSettingsFunction,
final Supplier<AsyncWriteThenReadOperationCursor<R>> operationSupplier,
@Nullable final ClientSession clientSession) {
AsyncWriteThenReadOperationCursor<R> operation = operationSupplier.get();
return getExecutor(timeoutSettingsFunction.apply(operations))
.execute(operation, getReadConcern(), clientSession);
}

<R> Mono<R> createWriteOperationMono(final Function<Operations<?>, TimeoutSettings> timeoutSettingsFunction,
final Supplier<WriteOperation<R>> operationSupplier, @Nullable final ClientSession clientSession) {
return createWriteOperationMono(() -> timeoutSettingsFunction.apply(operations), operationSupplier, clientSession);
Expand Down
16 changes: 16 additions & 0 deletions ...ctive-streams/src/main/com/mongodb/reactivestreams/client/internal/OperationExecutor.java
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Expand Up @@ -19,6 +19,8 @@
import com.mongodb.ReadConcern;
import com.mongodb.ReadPreference;
import com.mongodb.internal.TimeoutSettings;
import com.mongodb.internal.async.AsyncBatchCursor;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.ReadOperation;
import com.mongodb.internal.operation.WriteOperation;
import com.mongodb.lang.Nullable;
Expand Down Expand Up @@ -54,6 +56,20 @@ <T> Mono<T> execute(ReadOperation<?, T> operation, ReadPreference readPreference
*/
<T> Mono<T> execute(WriteOperation<T> operation, ReadConcern readConcern, @Nullable ClientSession session);

/**
* Execute an operation that writes and then reads a cursor within a single read-write binding.
*
* <p>The binding is acquired once and used for both phases, avoiding the need to narrow an
* {@code AsyncReadBinding} to an {@code AsyncWriteBinding}.
*
* @param operation the write-then-read operation.
* @param readConcern the read concern
* @param session the session to associate this operation with
* @param <T> the document type returned by the cursor.
*/
<T> Mono<AsyncBatchCursor<T>> execute(AsyncWriteThenReadOperationCursor<T> operation,
ReadConcern readConcern, @Nullable ClientSession session);

/**
* Create a new OperationExecutor with a specific timeout settings
*
Expand Down
47 changes: 47 additions & 0 deletions ...e-streams/src/main/com/mongodb/reactivestreams/client/internal/OperationExecutorImpl.java
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Expand Up @@ -33,6 +33,8 @@
import com.mongodb.internal.connection.ReadConcernAwareNoOpSessionContext;
import com.mongodb.internal.observability.micrometer.Span;
import com.mongodb.internal.observability.micrometer.TracingManager;
import com.mongodb.internal.async.AsyncBatchCursor;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.OperationHelper;
import com.mongodb.internal.operation.ReadOperation;
import com.mongodb.internal.operation.WriteOperation;
Expand Down Expand Up @@ -179,6 +181,51 @@ public <T> Mono<T> execute(final WriteOperation<T> operation, final ReadConcern
);
}

@Override
public <T> Mono<AsyncBatchCursor<T>> execute(final AsyncWriteThenReadOperationCursor<T> operation, final ReadConcern readConcern,
@Nullable final ClientSession session) {
isTrue("open", !mongoClient.getCluster().isClosed());
notNull("operation", operation);
notNull("readConcern", readConcern);

Comment on lines +184 to +190
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@strogiyotec strogiyotec Apr 29, 2026

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I added notifyOperationInitiated call , also implementationf of notifyOperationInitiated now also checked instance of AsyncWriteThenRead

if (session != null) {
session.notifyOperationInitiated(operation);
}

return Mono.from(subscriber ->
clientSessionHelper.withClientSession(session, this)
.flatMap(actualClientSession -> {
AsyncReadWriteBinding binding = getReadWriteBinding(primary(), actualClientSession, session == null);
RequestContext requestContext = getContext(subscriber);
OperationContext operationContext = getOperationContext(requestContext, actualClientSession, readConcern, operation.getCommandName())
.withSessionContext(new ClientSessionBinding.AsyncClientSessionContext(actualClientSession,
isImplicitSession(session), readConcern));
Span span = tracingManager.createOperationSpan(actualClientSession.getTransactionSpan(),
operationContext, operation.getCommandName(), operation.getNamespace());

return Mono.<AsyncBatchCursor<T>>create(sink -> operation.executeAsync(binding, operationContext, (result, t) -> {
try {
binding.release();
} finally {
if (t != null) {
Throwable exceptionToHandle = t instanceof MongoException
? OperationHelper.unwrap((MongoException) t) : t;
labelException(session, exceptionToHandle);
unpinServerAddressOnTransientTransactionError(session, exceptionToHandle);
if (span != null) {
span.error(t);
}
}
if (span != null) {
span.end();
}
sinkToCallback(sink).onResult(result, t);
}
}));
}).subscribe(subscriber)
);
}

@Override
public OperationExecutor withTimeoutSettings(final TimeoutSettings newTimeoutSettings) {
if (Objects.equals(timeoutSettings, newTimeoutSettings)) {
Expand Down
11 changes: 6 additions & 5 deletions ...om/mongodb/reactivestreams/client/internal/VoidWriteOperationThenCursorReadOperation.java
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Expand Up @@ -19,13 +19,13 @@
import com.mongodb.MongoNamespace;
import com.mongodb.internal.async.AsyncBatchCursor;
import com.mongodb.internal.async.SingleResultCallback;
import com.mongodb.internal.binding.AsyncReadBinding;
import com.mongodb.internal.binding.AsyncWriteBinding;
import com.mongodb.internal.binding.AsyncReadWriteBinding;
import com.mongodb.internal.connection.OperationContext;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.ReadOperationCursor;
import com.mongodb.internal.operation.WriteOperation;

class VoidWriteOperationThenCursorReadOperation<T> implements ReadOperationCursorAsyncOnly<T> {
class VoidWriteOperationThenCursorReadOperation<T> implements AsyncWriteThenReadOperationCursor<T> {
private final WriteOperation<Void> writeOperation;
private final ReadOperationCursor<T> cursorReadOperation;

Expand All @@ -46,8 +46,9 @@ public MongoNamespace getNamespace() {
}

@Override
public void executeAsync(final AsyncReadBinding binding, final OperationContext operationContext, final SingleResultCallback<AsyncBatchCursor<T>> callback) {
writeOperation.executeAsync((AsyncWriteBinding) binding, operationContext, (result, t) -> {
public void executeAsync(final AsyncReadWriteBinding binding, final OperationContext operationContext,
final SingleResultCallback<AsyncBatchCursor<T>> callback) {
writeOperation.executeAsync(binding, operationContext, (result, t) -> {
if (t != null) {
callback.onResult(null, t);
} else {
Expand Down
43 changes: 43 additions & 0 deletions ...src/test/unit/com/mongodb/reactivestreams/client/internal/MapReducePublisherImplTest.java
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Expand Up @@ -20,9 +20,13 @@
import com.mongodb.ReadPreference;
import com.mongodb.WriteConcern;
import com.mongodb.client.model.Sorts;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.MapReduceStatistics;
import com.mongodb.internal.operation.MapReduceToCollectionOperation;
import com.mongodb.internal.operation.MapReduceWithInlineResultsOperation;
import com.mongodb.reactivestreams.client.MapReducePublisher;


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removed empty line

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strogiyotec marked this conversation as resolved.
import org.bson.BsonDocument;
import org.bson.BsonInt32;
import org.bson.BsonJavaScript;
Expand All @@ -39,6 +43,7 @@
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertThrows;

@SuppressWarnings({"rawtypes", "deprecation"})
Expand All @@ -48,6 +53,44 @@ public class MapReducePublisherImplTest extends TestHelper {
private static final String REDUCE_FUNCTION = "reduceFunction(){}";
private static final String FINALIZE_FUNCTION = "finalizeFunction(){}";

@DisplayName("Non-inline MapReduce routes through the write-then-read executor path")
@Test
void shouldRouteNonInlineMapReduceThroughWriteThenReadPath() {
configureBatchCursor();
TestOperationExecutor executor = createOperationExecutor(asList(getBatchCursor()));

MapReducePublisher<Document> publisher =
new MapReducePublisherImpl<>(null, createMongoOperationPublisher(executor),
MAP_FUNCTION, REDUCE_FUNCTION)
.collectionName(NAMESPACE.getCollectionName());

Flux.from(publisher).blockFirst();

AsyncWriteThenReadOperationCursor<?> op = executor.getWriteThenReadOperation();
assertNotNull(op, "expected a write-then-read operation");
assertEquals(NAMESPACE, op.getNamespace());
// Must not fall through to the plain read-operation path.
assertNull(executor.getReadOperation());
}


@DisplayName("Inline MapReduce still routes through the read-operation path")
@Test
void shouldRouteInlineMapReduceThroughReadOperationPath() {
configureBatchCursor();
TestOperationExecutor executor = createOperationExecutor(asList(getBatchCursor()));

MapReducePublisher<Document> publisher =
new MapReducePublisherImpl<>(null, createMongoOperationPublisher(executor),
MAP_FUNCTION, REDUCE_FUNCTION); // no collectionName -> inline

Flux.from(publisher).blockFirst();

assertNotNull(executor.getReadOperation());
assertNull(executor.getWriteThenReadOperation());
}


@DisplayName("Should build the expected MapReduceWithInlineResultsOperation")
@Test
void shouldBuildTheExpectedMapReduceWithInlineResultsOperation() {
Expand Down
6 changes: 5 additions & 1 deletion ...eactive-streams/src/test/unit/com/mongodb/reactivestreams/client/internal/TestHelper.java
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Expand Up @@ -26,6 +26,7 @@
import com.mongodb.internal.bulk.IndexRequest;
import com.mongodb.internal.bulk.WriteRequest;
import com.mongodb.internal.client.model.FindOptions;
import com.mongodb.internal.operation.AsyncWriteThenReadOperationCursor;
import com.mongodb.internal.operation.ReadOperation;
import com.mongodb.internal.operation.WriteOperation;
import com.mongodb.lang.NonNull;
Expand Down Expand Up @@ -93,7 +94,10 @@ public class TestHelper {

Mockito.lenient().doAnswer(invocation -> Mono.empty())
.when(executor)
.execute(any(), any(), any());
.execute(any(WriteOperation.class), any(), any());
Mockito.lenient().doAnswer(invocation -> Mono.empty())
.when(executor)
.execute(any(AsyncWriteThenReadOperationCursor.class), any(), any());
Mockito.lenient().doAnswer(invocation -> Mono.empty())
.when(executor)
.execute(any(), any(), any(), any());
Expand Down
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