DATAMONGO-2344 - Fix slaveOK query option not applied correctly.

Since MongoDB 3.6 the slaveOk option translates to the primaryPreferred ReadPreference that is now again applied when executing a find operation.

Original pull request: #779.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/CursorPreparer.java

@@ -15,9 +15,15 @@
  */
 package org.springframework.data.mongodb.core;
 
-import org.bson.Document;
+import java.util.function.Function;
 
+import org.bson.Document;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+import com.mongodb.ReadPreference;
 import com.mongodb.client.FindIterable;
+import com.mongodb.client.MongoCollection;
 
 /**
  * Simple callback interface to allow customization of a {@link FindIterable}.
@@ -25,7 +31,14 @@ import com.mongodb.client.FindIterable;
  * @author Oliver Gierke
  * @author Christoph Strobl
  */
-interface CursorPreparer {
+interface CursorPreparer extends ReadPreferenceAware {
+
+	/**
+	 * Default {@link CursorPreparer} just passing on the given {@link FindIterable}.
+	 *
+	 * @since 2.2
+	 */
+	CursorPreparer NO_OP_PREPARER = (iterable -> iterable);
 
 	/**
 	 * Prepare the given cursor (apply limits, skips and so on). Returns the prepared cursor.
@@ -33,4 +46,37 @@ interface CursorPreparer {
 	 * @param cursor
 	 */
 	FindIterable<Document> prepare(FindIterable<Document> cursor);
+
+	/**
+	 * Apply query specific settings to {@link MongoCollection} and initate a find operation returning a
+	 * {@link FindIterable} via the given {@link Function find} function.
+	 * 
+	 * @param collection must not be {@literal null}.
+	 * @param find must not be {@literal null}.
+	 * @return
+	 * @throws IllegalArgumentException if one of the required arguments is {@literal null}.
+	 * @since 2.2
+	 */
+	default FindIterable<Document> initiateFind(MongoCollection<Document> collection,
+			Function<MongoCollection<Document>, FindIterable<Document>> find) {
+
+		Assert.notNull(collection, "Collection must not be null!");
+		Assert.notNull(find, "Find function must not be null!");
+
+		if (hasReadPreferences()) {
+			collection = collection.withReadPreference(getReadPreference());
+		}
+
+		return prepare(find.apply(collection));
+	}
+
+	/**
+	 * @return the {@link ReadPreference} to apply or {@literal null} if none defined.
+	 * @since 2.2
+	 */
+	@Override
+	@Nullable
+	default ReadPreference getReadPreference() {
+		return null;
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ExecutableFindOperationSupport.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.mongodb.core;
 
+import com.mongodb.ReadPreference;
 import lombok.AccessLevel;
 import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
@@ -267,6 +268,11 @@ class ExecutableFindOperationSupport implements ExecutableFindOperation {
 			this.limit = Optional.of(limit);
 			return this;
 		}
+
+		@Override
+		public ReadPreference getReadPreference() {
+			return delegate.getReadPreference();
+		}
 	}
 
 	/**

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/FindPublisherPreparer.java

@@ -15,14 +15,36 @@
  */
 package org.springframework.data.mongodb.core;
 
+import java.util.function.Function;
+
+import org.bson.Document;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+import com.mongodb.ReadPreference;
 import com.mongodb.reactivestreams.client.FindPublisher;
+import com.mongodb.reactivestreams.client.MongoCollection;
 
 /**
  * Simple callback interface to allow customization of a {@link FindPublisher}.
  *
  * @author Mark Paluch
+ * @author Christoph Strobl
  */
-interface FindPublisherPreparer {
+interface FindPublisherPreparer extends ReadPreferenceAware {
+
+	/**
+	 * Default {@link FindPublisherPreparer} just passing on the given {@link FindPublisher}.
+	 *
+	 * @since 2.2
+	 */
+	FindPublisherPreparer NO_OP_PREPARER = new FindPublisherPreparer() {
+
+		@Override
+		public <T> FindPublisher<T> prepare(FindPublisher<T> findPublisher) {
+			return findPublisher;
+		}
+	};
 
 	/**
 	 * Prepare the given cursor (apply limits, skips and so on). Returns the prepared cursor.
@@ -30,4 +52,37 @@ interface FindPublisherPreparer {
 	 * @param findPublisher must not be {@literal null}.
 	 */
 	<T> FindPublisher<T> prepare(FindPublisher<T> findPublisher);
+
+	/**
+	 * Apply query specific settings to {@link MongoCollection} and initate a find operation returning a
+	 * {@link FindPublisher} via the given {@link Function find} function.
+	 *
+	 * @param collection must not be {@literal null}.
+	 * @param find must not be {@literal null}.
+	 * @return
+	 * @throws IllegalArgumentException if one of the required arguments is {@literal null}.
+	 * @since 2.2
+	 */
+	default FindPublisher<Document> initiateFind(MongoCollection<Document> collection,
+			Function<MongoCollection<Document>, FindPublisher<Document>> find) {
+
+		Assert.notNull(collection, "Collection must not be null!");
+		Assert.notNull(find, "Find function must not be null!");
+
+		if (hasReadPreferences()) {
+			collection = collection.withReadPreference(getReadPreference());
+		}
+
+		return prepare(find.apply(collection));
+	}
+
+	/**
+	 * @return the {@link ReadPreference} to apply or {@literal null} if none defined.
+	 * @since 2.2
+	 */
+	@Override
+	@Nullable
+	default ReadPreference getReadPreference() {
+		return null;
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -105,6 +105,7 @@ import org.springframework.data.mongodb.core.mapreduce.MapReduceResults;
 import org.springframework.data.mongodb.core.query.Collation;
 import org.springframework.data.mongodb.core.query.Criteria;
 import org.springframework.data.mongodb.core.query.Meta;
+import org.springframework.data.mongodb.core.query.Meta.CursorOption;
 import org.springframework.data.mongodb.core.query.NearQuery;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.core.query.Update;
@@ -447,8 +448,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 			Document mappedFields = getMappedFieldsObject(query.getFieldsObject(), persistentEntity, returnType);
 			Document mappedQuery = queryMapper.getMappedObject(query.getQueryObject(), persistentEntity);
 
-			FindIterable<Document> cursor = new QueryCursorPreparer(query, entityType)
-					.prepare(collection.find(mappedQuery, Document.class).projection(mappedFields));
+			FindIterable<Document> cursor = new QueryCursorPreparer(query, entityType).initiateFind(collection,
+					col -> col.find(mappedQuery, Document.class).projection(mappedFields));
 
 			return new CloseableIterableCursorAdapter<>(cursor, exceptionTranslator,
 					new ProjectingReadCallback<>(mongoConverter, entityType, returnType, collectionName));
@@ -538,8 +539,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 					sortObject, fieldsObject, collectionName);
 		}
 
-		this.executeQueryInternal(new FindCallback(queryObject, fieldsObject, null), preparer, documentCallbackHandler,
-				collectionName);
+		this.executeQueryInternal(new FindCallback(queryObject, fieldsObject, null),
+				preparer != null ? preparer : CursorPreparer.NO_OP_PREPARER, documentCallbackHandler, collectionName);
 	}
 
 	/*
@@ -777,8 +778,9 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		Assert.notNull(mode, "BulkMode must not be null!");
 		Assert.hasText(collectionName, "Collection name must not be null or empty!");
 
-		DefaultBulkOperations operations = new DefaultBulkOperations(this, collectionName, new BulkOperationContext(mode,
-				Optional.ofNullable(getPersistentEntity(entityType)), queryMapper, updateMapper, eventPublisher, entityCallbacks));
+		DefaultBulkOperations operations = new DefaultBulkOperations(this, collectionName,
+				new BulkOperationContext(mode, Optional.ofNullable(getPersistentEntity(entityType)), queryMapper, updateMapper,
+						eventPublisher, entityCallbacks));
 
 		operations.setExceptionTranslator(exceptionTranslator);
 		operations.setDefaultWriteConcern(writeConcern);
@@ -814,8 +816,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		if (ObjectUtils.isEmpty(query.getSortObject())) {
 
 			return doFindOne(collectionName, query.getQueryObject(), query.getFieldsObject(),
-					operations.forType(entityClass).getCollation(query).map(Collation::toMongoCollation).orElse(null),
-					entityClass);
+					new QueryCursorPreparer(query, entityClass), entityClass);
 		} else {
 			query.limit(1);
 			List<T> results = find(query, entityClass, collectionName);
@@ -933,6 +934,11 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 						serializeToJsonSafely(mappedQuery), field, collectionName);
 			}
 
+			QueryCursorPreparer preparer = new QueryCursorPreparer(query, entityClass);
+			if (preparer.hasReadPreferences()) {
+				collection = collection.withReadPreference(preparer.getReadPreference());
+			}
+
 			DistinctIterable<T> iterable = collection.distinct(mappedFieldName, mappedQuery, mongoDriverCompatibleType);
 
 			return operations.forType(entityClass) //
@@ -1007,8 +1013,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		Assert.notNull(collectionName, "CollectionName must not be null!");
 		Assert.notNull(returnType, "ReturnType must not be null!");
 
-		String collection = StringUtils.hasText(collectionName) ? collectionName
-				: getCollectionName(domainType);
+		String collection = StringUtils.hasText(collectionName) ? collectionName : getCollectionName(domainType);
 		String distanceField = operations.nearQueryDistanceFieldName(domainType);
 
 		Aggregation $geoNear = TypedAggregation.newAggregation(domainType, Aggregation.geoNear(near, distanceField))
@@ -1039,8 +1044,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	@Nullable
 	@Override
 	public <T> T findAndModify(Query query, Update update, Class<T> entityClass) {
-		return findAndModify(query, update, new FindAndModifyOptions(), entityClass,
-				getCollectionName(entityClass));
+		return findAndModify(query, update, new FindAndModifyOptions(), entityClass, getCollectionName(entityClass));
 	}
 
 	@Nullable
@@ -1296,8 +1300,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 		Assert.notNull(batchToSave, "BatchToSave must not be null!");
 
-		return (Collection<T>) doInsertBatch(getCollectionName(entityClass), batchToSave,
-				this.mongoConverter);
+		return (Collection<T>) doInsertBatch(getCollectionName(entityClass), batchToSave, this.mongoConverter);
 	}
 
 	@Override
@@ -1795,7 +1798,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		return executeFindMultiInternal(
 				new FindCallback(new Document(), new Document(),
 						operations.forType(entityClass).getCollation().map(Collation::toMongoCollation).orElse(null)),
-				null, new ReadDocumentCallback<>(mongoConverter, entityClass, collectionName), collectionName);
+				CursorPreparer.NO_OP_PREPARER, new ReadDocumentCallback<>(mongoConverter, entityClass, collectionName),
+				collectionName);
 	}
 
 	@Override
@@ -2435,7 +2439,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @return the {@link List} of converted objects.
 	 */
 	protected <T> T doFindOne(String collectionName, Document query, Document fields, Class<T> entityClass) {
-		return doFindOne(collectionName, query, fields, null, entityClass);
+		return doFindOne(collectionName, query, fields, CursorPreparer.NO_OP_PREPARER, entityClass);
 	}
 
 	/**
@@ -2446,12 +2450,13 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @param query the query document that specifies the criteria used to find a record.
 	 * @param fields the document that specifies the fields to be returned.
 	 * @param entityClass the parameterized type of the returned list.
+	 * @param preparer the preparer used to modify the cursor on execution.
 	 * @return the {@link List} of converted objects.
 	 * @since 2.2
 	 */
 	@SuppressWarnings("ConstantConditions")
-	protected <T> T doFindOne(String collectionName, Document query, Document fields,
-			@Nullable com.mongodb.client.model.Collation collation, Class<T> entityClass) {
+	protected <T> T doFindOne(String collectionName, Document query, Document fields, CursorPreparer preparer,
+			Class<T> entityClass) {
 
 		MongoPersistentEntity<?> entity = mappingContext.getPersistentEntity(entityClass);
 		Document mappedQuery = queryMapper.getMappedObject(query, entity);
@@ -2462,7 +2467,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 					mappedFields, entityClass, collectionName);
 		}
 
-		return executeFindOneInternal(new FindOneCallback(mappedQuery, mappedFields, collation),
+		return executeFindOneInternal(new FindOneCallback(mappedQuery, mappedFields, preparer),
 				new ReadDocumentCallback<>(this.mongoConverter, entityClass, collectionName), collectionName);
 	}
 
@@ -2513,8 +2518,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 					serializeToJsonSafely(mappedQuery), mappedFields, entityClass, collectionName);
 		}
 
-		return executeFindMultiInternal(new FindCallback(mappedQuery, mappedFields, null), preparer, objectCallback,
-				collectionName);
+		return executeFindMultiInternal(new FindCallback(mappedQuery, mappedFields, null),
+				preparer != null ? preparer : CursorPreparer.NO_OP_PREPARER, objectCallback, collectionName);
 	}
 
 	/**
@@ -2736,6 +2741,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 			DocumentCallback<T> objectCallback, String collectionName) {
 
 		try {
+
 			T result = objectCallback
 					.doWith(collectionCallback.doInCollection(getAndPrepareCollection(doGetDatabase(), collectionName)));
 			return result;
@@ -2763,7 +2769,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @return
 	 */
 	private <T> List<T> executeFindMultiInternal(CollectionCallback<FindIterable<Document>> collectionCallback,
-			@Nullable CursorPreparer preparer, DocumentCallback<T> objectCallback, String collectionName) {
+			CursorPreparer preparer, DocumentCallback<T> objectCallback, String collectionName) {
 
 		try {
 
@@ -2771,14 +2777,9 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 			try {
 
-				FindIterable<Document> iterable = collectionCallback
-						.doInCollection(getAndPrepareCollection(doGetDatabase(), collectionName));
-
-				if (preparer != null) {
-					iterable = preparer.prepare(iterable);
-				}
-
-				cursor = iterable.iterator();
+				cursor = preparer
+						.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
+						.iterator();
 
 				List<T> result = new ArrayList<>();
 
@@ -2800,21 +2801,17 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	}
 
 	private void executeQueryInternal(CollectionCallback<FindIterable<Document>> collectionCallback,
-			@Nullable CursorPreparer preparer, DocumentCallbackHandler callbackHandler, String collectionName) {
+			CursorPreparer preparer, DocumentCallbackHandler callbackHandler, String collectionName) {
 
 		try {
 
 			MongoCursor<Document> cursor = null;
 
 			try {
-				FindIterable<Document> iterable = collectionCallback
-						.doInCollection(getAndPrepareCollection(doGetDatabase(), collectionName));
 
-				if (preparer != null) {
-					iterable = preparer.prepare(iterable);
-				}
-
-				cursor = iterable.iterator();
+				cursor = preparer
+						.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
+						.iterator();
 
 				while (cursor.hasNext()) {
 					callbackHandler.processDocument(cursor.next());
@@ -2908,21 +2905,19 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 		private final Document query;
 		private final Optional<Document> fields;
-		private final @Nullable com.mongodb.client.model.Collation collation;
+		private final CursorPreparer cursorPreparer;
 
-		public FindOneCallback(Document query, Document fields, @Nullable com.mongodb.client.model.Collation collation) {
+		FindOneCallback(Document query, Document fields, CursorPreparer preparer) {
 
 			this.query = query;
 			this.fields = Optional.of(fields).filter(it -> !ObjectUtils.isEmpty(fields));
-			this.collation = collation;
+			this.cursorPreparer = preparer;
 		}
 
+		@Override
 		public Document doInCollection(MongoCollection<Document> collection) throws MongoException, DataAccessException {
 
-			FindIterable<Document> iterable = collection.find(query, Document.class);
-			if (collation != null) {
-				iterable = iterable.collation(collation);
-			}
+			FindIterable<Document> iterable = cursorPreparer.initiateFind(collection, col -> col.find(query, Document.class));
 
 			if (LOGGER.isDebugEnabled()) {
 
@@ -3318,6 +3313,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 							case PARTIAL:
 								cursorToUse = cursorToUse.partial(true);
 								break;
+							case SLAVE_OK:
+								break;
 							default:
 								throw new IllegalArgumentException(String.format("%s is no supported flag.", option));
 						}
@@ -3330,6 +3327,11 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 			return cursorToUse;
 		}
+
+		@Override
+		public ReadPreference getReadPreference() {
+			return query.getMeta().getFlags().contains(CursorOption.SLAVE_OK) ? ReadPreference.primaryPreferred() : null;
+		}
 	}
 
 	/**

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoTemplate.java

@@ -102,6 +102,7 @@ import org.springframework.data.mongodb.core.mapping.event.ReactiveBeforeSaveCal
 import org.springframework.data.mongodb.core.mapreduce.MapReduceOptions;
 import org.springframework.data.mongodb.core.query.Collation;
 import org.springframework.data.mongodb.core.query.Meta;
+import org.springframework.data.mongodb.core.query.Meta.CursorOption;
 import org.springframework.data.mongodb.core.query.NearQuery;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.core.query.Update;
@@ -803,7 +804,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 		if (ObjectUtils.isEmpty(query.getSortObject())) {
 			return doFindOne(collectionName, query.getQueryObject(), query.getFieldsObject(), entityClass,
-					operations.forType(entityClass).getCollation(query).orElse(null));
+					new QueryFindPublisherPreparer(query, entityClass));
 		}
 
 		query.limit(1);
@@ -891,7 +892,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 		String idKey = operations.getIdPropertyName(entityClass);
 
-		return doFindOne(collectionName, new Document(idKey, id), null, entityClass, null);
+		return doFindOne(collectionName, new Document(idKey, id), null, entityClass, (Collation) null);
 	}
 
 	/*
@@ -932,6 +933,11 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 						serializeToJsonSafely(mappedQuery), field, collectionName);
 			}
 
+			FindPublisherPreparer preparer = new QueryFindPublisherPreparer(query, entityClass);
+			if (preparer.hasReadPreferences()) {
+				collection = collection.withReadPreference(preparer.getReadPreference());
+			}
+
 			DistinctPublisher<T> publisher = collection.distinct(mappedFieldName, mappedQuery, mongoDriverCompatibleType);
 			return operations.forType(entityClass).getCollation(query) //
 					.map(Collation::toMongoCollation) //
@@ -1981,7 +1987,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * @see org.springframework.data.mongodb.core.ReactiveMongoOperations#findAll(java.lang.Class, java.lang.String)
 	 */
 	public <T> Flux<T> findAll(Class<T> entityClass, String collectionName) {
-		return executeFindMultiInternal(new FindCallback(null), null,
+		return executeFindMultiInternal(new FindCallback(null), FindPublisherPreparer.NO_OP_PREPARER,
 				new ReadDocumentCallback<>(mongoConverter, entityClass, collectionName), collectionName);
 	}
 
@@ -2035,8 +2041,9 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 			LOGGER.debug(String.format("find for class: %s in collection: %s", entityClass, collectionName));
 
 			return executeFindMultiInternal(
-					collection -> new FindCallback(null).doInCollection(collection).cursorType(CursorType.TailableAwait), null,
-					new ReadDocumentCallback<>(mongoConverter, entityClass, collectionName), collectionName);
+					collection -> new FindCallback(null).doInCollection(collection).cursorType(CursorType.TailableAwait),
+					FindPublisherPreparer.NO_OP_PREPARER, new ReadDocumentCallback<>(mongoConverter, entityClass, collectionName),
+					collectionName);
 		}
 
 		return doFind(collectionName, query.getQueryObject(), query.getFieldsObject(), entityClass,
@@ -2327,6 +2334,29 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	protected <T> Mono<T> doFindOne(String collectionName, Document query, @Nullable Document fields,
 			Class<T> entityClass, @Nullable Collation collation) {
 
+		return doFindOne(collectionName, query, fields, entityClass, new FindPublisherPreparer() {
+			@Override
+			public <T> FindPublisher<T> prepare(FindPublisher<T> findPublisher) {
+				return collation != null ? findPublisher.collation(collation.toMongoCollation()) : findPublisher;
+			}
+		});
+	}
+
+	/**
+	 * Map the results of an ad-hoc query on the default MongoDB collection to an object using the template's converter.
+	 * The query document is specified as a standard {@link Document} and so is the fields specification.
+	 *
+	 * @param collectionName name of the collection to retrieve the objects from.
+	 * @param query the query document that specifies the criteria used to find a record.
+	 * @param fields the document that specifies the fields to be returned.
+	 * @param entityClass the parameterized type of the returned list.
+	 * @param preparer the preparer modifying collection and publisher to fit the needs.
+	 * @return the {@link List} of converted objects.
+	 * @since 2.2
+	 */
+	protected <T> Mono<T> doFindOne(String collectionName, Document query, @Nullable Document fields,
+			Class<T> entityClass, FindPublisherPreparer preparer) {
+
 		MongoPersistentEntity<?> entity = mappingContext.getPersistentEntity(entityClass);
 		Document mappedQuery = queryMapper.getMappedObject(query, entity);
 		Document mappedFields = fields == null ? null : queryMapper.getMappedObject(fields, entity);
@@ -2336,7 +2366,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 					serializeToJsonSafely(query), mappedFields, entityClass, collectionName));
 		}
 
-		return executeFindOneInternal(new FindOneCallback(mappedQuery, mappedFields, collation),
+		return executeFindOneInternal(new FindOneCallback(mappedQuery, mappedFields, preparer),
 				new ReadDocumentCallback<>(this.mongoConverter, entityClass, collectionName), collectionName);
 	}
 
@@ -2706,13 +2736,8 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 			@Nullable FindPublisherPreparer preparer, DocumentCallback<T> objectCallback, String collectionName) {
 
 		return createFlux(collectionName, collection -> {
-
-			FindPublisher<Document> findPublisher = collectionCallback.doInCollection(collection);
-
-			if (preparer != null) {
-				findPublisher = preparer.prepare(findPublisher);
-			}
-			return Flux.from(findPublisher).map(objectCallback::doWith);
+			return Flux.from(preparer.initiateFind(collection, collectionCallback::doInCollection))
+					.map(objectCallback::doWith);
 		});
 	}
 
@@ -2784,37 +2809,36 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 *
 	 * @author Oliver Gierke
 	 * @author Thomas Risberg
+	 * @author Christoph Strobl
 	 */
 	private static class FindOneCallback implements ReactiveCollectionCallback<Document> {
 
 		private final Document query;
 		private final Optional<Document> fields;
-		private final Optional<Collation> collation;
+		private final FindPublisherPreparer preparer;
 
-		FindOneCallback(Document query, @Nullable Document fields, @Nullable Collation collation) {
+		FindOneCallback(Document query, @Nullable Document fields, FindPublisherPreparer preparer) {
 			this.query = query;
 			this.fields = Optional.ofNullable(fields);
-			this.collation = Optional.ofNullable(collation);
+			this.preparer = preparer;
 		}
 
 		@Override
 		public Publisher<Document> doInCollection(MongoCollection<Document> collection)
 				throws MongoException, DataAccessException {
 
-			FindPublisher<Document> publisher = collection.find(query, Document.class);
-
 			if (LOGGER.isDebugEnabled()) {
 
 				LOGGER.debug("findOne using query: {} fields: {} in db.collection: {}", serializeToJsonSafely(query),
 						serializeToJsonSafely(fields.orElseGet(Document::new)), collection.getNamespace().getFullName());
 			}
 
+			FindPublisher<Document> publisher = preparer.initiateFind(collection, col -> col.find(query, Document.class));
+
 			if (fields.isPresent()) {
 				publisher = publisher.projection(fields.get());
 			}
 
-			publisher = collation.map(Collation::toMongoCollation).map(publisher::collation).orElse(publisher);
-
 			return publisher.limit(1).first();
 		}
 	}
@@ -3221,6 +3245,11 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 			return findPublisherToUse;
 		}
+
+		@Override
+		public ReadPreference getReadPreference() {
+			return query.getMeta().getFlags().contains(CursorOption.SLAVE_OK) ? ReadPreference.primaryPreferred() : null;
+		}
 	}
 
 	class TailingQueryFindPublisherPreparer extends QueryFindPublisherPreparer {

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReadPreferenceAware.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 org.springframework.data.mongodb.core;
+
+import org.springframework.lang.Nullable;
+
+import com.mongodb.ReadPreference;
+
+/**
+ * @author Christoph Strobl
+ * @since 2.2
+ */
+interface ReadPreferenceAware {
+
+	/**
+	 * @return {@literal true} if a {@link ReadPreference} is set.
+	 */
+	default boolean hasReadPreferences() {
+		return getReadPreference() != null;
+	}
+
+	/**
+	 * @return the {@link ReadPreference} to apply or {@literal null} if none set.
+	 */
+	@Nullable
+	ReadPreference getReadPreference();
+}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateUnitTests.java

@@ -935,7 +935,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733
 	public void appliesFieldsWhenInterfaceProjectionIsClosedAndQueryDoesNotDefineFields() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonProjection.class, null);
+		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonProjection.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document("firstname", 1)));
 	}
@@ -943,7 +944,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733
 	public void doesNotApplyFieldsWhenInterfaceProjectionIsClosedAndQueryDefinesFields() {
 
-		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, PersonProjection.class, null);
+		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, PersonProjection.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document("bar", 1)));
 	}
@@ -951,7 +953,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733
 	public void doesNotApplyFieldsWhenInterfaceProjectionIsOpen() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonSpELProjection.class, null);
+		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonSpELProjection.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document()));
 	}
@@ -959,7 +962,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733, DATAMONGO-2041
 	public void appliesFieldsToDtoProjection() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, Jedi.class, null);
+		template.doFind("star-wars", new Document(), new Document(), Person.class, Jedi.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document("firstname", 1)));
 	}
@@ -967,7 +971,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733
 	public void doesNotApplyFieldsToDtoProjectionWhenQueryDefinesFields() {
 
-		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, Jedi.class, null);
+		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, Jedi.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document("bar", 1)));
 	}
@@ -975,7 +980,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733
 	public void doesNotApplyFieldsWhenTargetIsNotAProjection() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, Person.class, null);
+		template.doFind("star-wars", new Document(), new Document(), Person.class, Person.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document()));
 	}
@@ -983,7 +989,8 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 	@Test // DATAMONGO-1733
 	public void doesNotApplyFieldsWhenTargetExtendsDomainType() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonExtended.class, null);
+		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonExtended.class,
+				CursorPreparer.NO_OP_PREPARER);
 
 		verify(findIterable).projection(eq(new Document()));
 	}
@@ -1637,6 +1644,37 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 		Assertions.assertThat(ReflectionTestUtils.getField(template, "entityCallbacks")).isSameAs(callbacks);
 	}
 
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForFind() {
+
+		template.find(new Query().slaveOk(), AutogenerateableId.class);
+
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForFindOne() {
+
+		template.findOne(new Query().slaveOk(), AutogenerateableId.class);
+
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForFindDistinct() {
+
+		template.findDistinct(new Query().slaveOk(), "name", AutogenerateableId.class, String.class);
+
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForStream() {
+
+		template.stream(new Query().slaveOk(), AutogenerateableId.class);
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
 	class AutogenerateableId {
 
 		@Id BigInteger id;

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ReactiveMongoTemplateUnitTests.java

@@ -40,7 +40,6 @@ import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
 import org.reactivestreams.Publisher;
-
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.support.StaticApplicationContext;
@@ -65,6 +64,7 @@ import org.springframework.lang.Nullable;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.util.CollectionUtils;
 
+import com.mongodb.ReadPreference;
 import com.mongodb.client.model.CountOptions;
 import com.mongodb.client.model.CreateCollectionOptions;
 import com.mongodb.client.model.DeleteOptions;
@@ -121,6 +121,7 @@ public class ReactiveMongoTemplateUnitTests {
 		when(db.getCollection(any(), any())).thenReturn(collection);
 		when(db.runCommand(any(), any(Class.class))).thenReturn(runCommandPublisher);
 		when(db.createCollection(any(), any(CreateCollectionOptions.class))).thenReturn(runCommandPublisher);
+		when(collection.withReadPreference(any())).thenReturn(collection);
 		when(collection.find(any(Class.class))).thenReturn(findPublisher);
 		when(collection.find(any(Document.class), any(Class.class))).thenReturn(findPublisher);
 		when(collection.aggregate(anyList())).thenReturn(aggregatePublisher);
@@ -324,8 +325,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719
 	public void appliesFieldsWhenInterfaceProjectionIsClosedAndQueryDoesNotDefineFields() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonProjection.class, null)
-				.subscribe();
+		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonProjection.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher).projection(eq(new Document("firstname", 1)));
 	}
@@ -333,8 +334,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719
 	public void doesNotApplyFieldsWhenInterfaceProjectionIsClosedAndQueryDefinesFields() {
 
-		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, PersonProjection.class, null)
-				.subscribe();
+		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, PersonProjection.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher).projection(eq(new Document("bar", 1)));
 	}
@@ -342,8 +343,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719
 	public void doesNotApplyFieldsWhenInterfaceProjectionIsOpen() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonSpELProjection.class, null)
-				.subscribe();
+		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonSpELProjection.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher, never()).projection(any());
 	}
@@ -351,7 +352,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719, DATAMONGO-2041
 	public void appliesFieldsToDtoProjection() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, Jedi.class, null).subscribe();
+		template.doFind("star-wars", new Document(), new Document(), Person.class, Jedi.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher).projection(eq(new Document("firstname", 1)));
 	}
@@ -359,7 +361,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719
 	public void doesNotApplyFieldsToDtoProjectionWhenQueryDefinesFields() {
 
-		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, Jedi.class, null).subscribe();
+		template.doFind("star-wars", new Document(), new Document("bar", 1), Person.class, Jedi.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher).projection(eq(new Document("bar", 1)));
 	}
@@ -367,7 +370,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719
 	public void doesNotApplyFieldsWhenTargetIsNotAProjection() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, Person.class, null).subscribe();
+		template.doFind("star-wars", new Document(), new Document(), Person.class, Person.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher, never()).projection(any());
 	}
@@ -375,7 +379,8 @@ public class ReactiveMongoTemplateUnitTests {
 	@Test // DATAMONGO-1719
 	public void doesNotApplyFieldsWhenTargetExtendsDomainType() {
 
-		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonExtended.class, null).subscribe();
+		template.doFind("star-wars", new Document(), new Document(), Person.class, PersonExtended.class,
+				FindPublisherPreparer.NO_OP_PREPARER).subscribe();
 
 		verify(findPublisher, never()).projection(any());
 	}
@@ -804,6 +809,30 @@ public class ReactiveMongoTemplateUnitTests {
 		Assertions.assertThat(ReflectionTestUtils.getField(template, "entityCallbacks")).isSameAs(callbacks);
 	}
 
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForFind() {
+
+		template.find(new Query().slaveOk(), AutogenerateableId.class).subscribe();
+
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForFindOne() {
+
+		template.findOne(new Query().slaveOk(), AutogenerateableId.class).subscribe();
+
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
+	@Test // DATAMONGO-2344
+	public void slaveOkQueryOptionShouldApplyPrimaryPreferredReadPreferenceForFindDistinct() {
+
+		template.findDistinct(new Query().slaveOk(), "name", AutogenerateableId.class, String.class).subscribe();
+
+		verify(collection).withReadPreference(eq(ReadPreference.primaryPreferred()));
+	}
+
 	@Data
 	@org.springframework.data.mongodb.core.mapping.Document(collection = "star-wars")
 	static class Person {