DATAMONGO-2490 - Fix dbref fetching during ongoing transaction.

Original pull request: #875.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/MongoDatabaseUtils.java

@@ -79,7 +79,7 @@ public class MongoDatabaseUtils {
 	 * @param factory the {@link MongoDbFactory} to get the {@link MongoDatabase} from.
 	 * @return the {@link MongoDatabase} that is potentially associated with a transactional {@link ClientSession}.
 	 */
-	public static MongoDatabase getDatabase(String dbName, MongoDbFactory factory) {
+	public static MongoDatabase getDatabase(@Nullable String dbName, MongoDbFactory factory) {
 		return doGetMongoDatabase(dbName, factory, SessionSynchronization.ON_ACTUAL_TRANSACTION);
 	}
 
@@ -88,13 +88,13 @@ public class MongoDatabaseUtils {
 	 * <p />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the current
 	 * {@link Thread} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
-	 * 
+	 *
 	 * @param dbName the name of the {@link MongoDatabase} to get.
 	 * @param factory the {@link MongoDbFactory} to get the {@link MongoDatabase} from.
 	 * @param sessionSynchronization the synchronization to use. Must not be {@literal null}.
 	 * @return the {@link MongoDatabase} that is potentially associated with a transactional {@link ClientSession}.
 	 */
-	public static MongoDatabase getDatabase(String dbName, MongoDbFactory factory,
+	public static MongoDatabase getDatabase(@Nullable String dbName, MongoDbFactory factory,
 			SessionSynchronization sessionSynchronization) {
 		return doGetMongoDatabase(dbName, factory, sessionSynchronization);
 	}

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

@@ -45,6 +45,7 @@ import org.springframework.dao.support.PersistenceExceptionTranslator;
 import org.springframework.data.mongodb.ClientSessionException;
 import org.springframework.data.mongodb.LazyLoadingException;
 import org.springframework.data.mongodb.MongoDbFactory;
+import org.springframework.data.mongodb.MongoDatabaseUtils;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.lang.Nullable;
 import org.springframework.objenesis.ObjenesisStd;
@@ -497,7 +498,7 @@ public class DefaultDbRefResolver implements DbRefResolver {
 	 */
 	protected MongoCollection<Document> getCollection(DBRef dbref) {
 
-		return (StringUtils.hasText(dbref.getDatabaseName()) ? mongoDbFactory.getDb(dbref.getDatabaseName())
-				: mongoDbFactory.getDb()).getCollection(dbref.getCollectionName(), Document.class);
+		return MongoDatabaseUtils.getDatabase(dbref.getDatabaseName(), mongoDbFactory)
+				.getCollection(dbref.getCollectionName(), Document.class);
 	}
 }

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

@@ -31,6 +31,7 @@ import org.junit.Test;
 import org.junit.rules.TestRule;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
+import org.springframework.data.mongodb.core.mapping.DBRef;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.test.util.MongoTestUtils;
 import org.springframework.data.mongodb.test.util.MongoVersion;
@@ -54,6 +55,7 @@ public class ClientSessionTests {
 
 	private static final String DB_NAME = "client-session-tests";
 	private static final String COLLECTION_NAME = "test";
+	private static final String REF_COLLECTION_NAME = "test-with-ref";
 
 	MongoTemplate template;
 	MongoClient client;
@@ -154,6 +156,31 @@ public class ClientSessionTests {
 		assertThat(template.exists(query(where("id").is(saved.getId())), SomeDoc.class)).isFalse();
 	}
 
+	@Test // DATAMONGO-2490
+	public void shouldBeAbleToReadDbRefDuringTransaction() {
+
+		SomeDoc ref = new SomeDoc("ref-1", "da value");
+		WithDbRef source = new WithDbRef("source-1", "da source", ref);
+
+		ClientSession session = mongoClient.startSession(ClientSessionOptions.builder().causallyConsistent(true).build());
+
+		assertThat(session.getOperationTime()).isNull();
+
+		session.startTransaction();
+
+		WithDbRef saved = template.withSession(() -> session).execute(action -> {
+
+			template.save(ref);
+			template.save(source);
+
+			return template.findOne(query(where("id").is(source.id)), WithDbRef.class);
+		});
+
+		assertThat(saved.getSomeDocRef()).isEqualTo(ref);
+
+		session.abortTransaction();
+	}
+
 	@Data
 	@AllArgsConstructor
 	@org.springframework.data.mongodb.core.mapping.Document(COLLECTION_NAME)
@@ -163,4 +190,14 @@ public class ClientSessionTests {
 		String value;
 	}
 
+	@Data
+	@AllArgsConstructor
+	@org.springframework.data.mongodb.core.mapping.Document(REF_COLLECTION_NAME)
+	static class WithDbRef {
+
+		@Id String id;
+		String value;
+		@DBRef SomeDoc someDocRef;
+	}
+
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/PersonRepositoryTransactionalTests.java

@@ -20,6 +20,7 @@ import static org.springframework.data.mongodb.test.util.MongoTestUtils.*;
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.Optional;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 import org.bson.Document;
@@ -175,6 +176,25 @@ public class PersonRepositoryTransactionalTests {
 		assertAfterTransaction(hu).isNotPresent();
 	}
 
+	@Test // DATAMONGO-2490
+	public void shouldBeAbleToReadDbRefDuringTransaction() {
+
+		User rat = new User();
+		rat.setUsername("rat");
+
+		template.save(rat);
+
+		Person elene = new Person("Elene", "Cromwyll", 18);
+		elene.setCoworker(rat);
+
+		repository.save(elene);
+
+		Optional<Person> loaded = repository.findById(elene.getId());
+		assertThat(loaded).isPresent();
+		assertThat(loaded.get().getCoworker()).isNotNull();
+		assertThat(loaded.get().getCoworker().getUsername()).isEqualTo(rat.getUsername());
+	}
+
 	private AfterTransactionAssertion assertAfterTransaction(Person person) {
 
 		AfterTransactionAssertion assertion = new AfterTransactionAssertion<>(new Persistable<Object>() {