Allow access to mongoDatabaseFactory used in ReactiveMongoTemplate.

By offering a getter method for the ReactiveMongoDatabaseFactory users subclassing ReactiveMongoTemplate could evaluate the current transaction state via ReactiveMongoDatabaseUtils.isTransactionActive(getDatabaseFactory()).
This change also aligns the reactive and imperative template implementation in that regard.

Closes #3540
Original pull request: #3541.

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

@@ -28,7 +28,6 @@ import org.bson.Document;
 import org.bson.conversions.Bson;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import org.springframework.beans.BeansException;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
@@ -3454,7 +3453,20 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		}
 	}
 
+	/**
+	 * @deprecated since 3.1.4. Use {@link #getMongoDatabaseFactory()} instead.
+	 * @return the {@link MongoDatabaseFactory} in use.
+	 */
+	@Deprecated
 	public MongoDatabaseFactory getMongoDbFactory() {
+		return getMongoDatabaseFactory();
+	}
+
+	/**
+	 * @return the {@link MongoDatabaseFactory} in use.
+	 * @since 3.1.4
+	 */
+	public MongoDatabaseFactory getMongoDatabaseFactory() {
 		return mongoDbFactory;
 	}
 

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

@@ -2730,6 +2730,14 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		return potentiallyForceAcknowledgedWrite(wc);
 	}
 
+	/**
+	 * @return the {@link MongoDatabaseFactory} in use.
+	 * @since 3.1.4
+	 */
+	public ReactiveMongoDatabaseFactory getMongoDatabaseFactory() {
+		return mongoDatabaseFactory;
+	}
+
 	@Nullable
 	private WriteConcern potentiallyForceAcknowledgedWrite(@Nullable WriteConcern wc) {