DATAMONGO-2241 - Polishing.

Ensure to have to DbRefResolver operate within the session while reusing the MappingContext.

Original Pull Request: #734

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

@@ -33,7 +33,6 @@ import org.bson.codecs.Codec;
 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;
@@ -260,7 +259,15 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		this.mongoDbFactory = dbFactory;
 		this.exceptionTranslator = that.exceptionTranslator;
 		this.sessionSynchronization = that.sessionSynchronization;
-		this.mongoConverter = that.mongoConverter;
+
+		// we need to (re)create the MappingMongoConverter as we need to have it use a DbRefResolver that operates within
+		// the sames session. Otherwise loading referenced objects would happen outside of it.
+		if (that.mongoConverter instanceof MappingMongoConverter) {
+			this.mongoConverter = ((MappingMongoConverter) that.mongoConverter).with(dbFactory);
+		} else {
+			this.mongoConverter = that.mongoConverter;
+		}
+
 		this.queryMapper = that.queryMapper;
 		this.updateMapper = that.updateMapper;
 		this.schemaMapper = that.schemaMapper;

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

@@ -28,7 +28,9 @@ import org.springframework.context.ApplicationContextAware;
 import org.springframework.core.CollectionFactory;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.support.DefaultConversionService;
+import org.springframework.data.convert.CustomConversions;
 import org.springframework.data.convert.EntityInstantiator;
+import org.springframework.data.convert.EntityInstantiators;
 import org.springframework.data.convert.TypeMapper;
 import org.springframework.data.mapping.Association;
 import org.springframework.data.mapping.MappingException;
@@ -1596,6 +1598,26 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 		return dbRefResolver.bulkFetch(references);
 	}
 
+
+	/**
+	 * Create a new {@link MappingMongoConverter} using the given {@link MongoDbFactory} when loading {@link DBRef}.
+	 *
+	 * @return new instance of {@link MappingMongoConverter}. Never {@literal null}.
+	 * @since 2.1.6
+	 */
+	public MappingMongoConverter with(MongoDbFactory dbFactory) {
+
+		MappingMongoConverter target = new MappingMongoConverter(new DefaultDbRefResolver(dbFactory), mappingContext);
+		target.applicationContext = applicationContext;
+		target.conversions = conversions;
+		target.spELContext = spELContext;
+		target.setInstantiators(instantiators);
+		target.typeMapper = typeMapper;
+		target.afterPropertiesSet();
+
+		return target;
+	}
+
 	/**
 	 * Returns whether the given {@link Iterable} contains {@link DBRef} instances all pointing to the same collection.
 	 *

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

@@ -29,15 +29,15 @@ import org.junit.ClassRule;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TestRule;
-
 import org.springframework.data.annotation.Id;
-import org.springframework.data.mongodb.core.convert.MongoConverter;
+import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.test.util.MongoTestUtils;
 import org.springframework.data.mongodb.test.util.MongoVersion;
 import org.springframework.data.mongodb.test.util.MongoVersionRule;
 import org.springframework.data.mongodb.test.util.ReplicaSet;
 import org.springframework.data.util.Version;
+import org.springframework.test.util.ReflectionTestUtils;
 
 import com.mongodb.ClientSessionOptions;
 import com.mongodb.MongoClient;
@@ -92,15 +92,19 @@ public class ClientSessionTests {
 	}
 
 	@Test // DATAMONGO-2241
-	public void shouldReuseConfiguredConverter() {
+	public void shouldReuseConfiguredInfrastructure() {
 
 		ClientSession session = client.startSession(ClientSessionOptions.builder().causallyConsistent(true).build());
 
-		MongoConverter converter = template.getConverter();
-		MongoConverter sessionTemplateConverter = template.withSession(() -> session)
-				.execute(MongoOperations::getConverter);
+		MappingMongoConverter source = MappingMongoConverter.class.cast(template.getConverter());
+		MappingMongoConverter sessionTemplateConverter = MappingMongoConverter.class
+				.cast(template.withSession(() -> session).execute(MongoOperations::getConverter));
 
-		assertThat(sessionTemplateConverter).isSameAs(converter);
+		assertThat(sessionTemplateConverter.getMappingContext()).isSameAs(source.getMappingContext());
+		assertThat(ReflectionTestUtils.getField(sessionTemplateConverter, "conversions"))
+				.isSameAs(ReflectionTestUtils.getField(source, "conversions"));
+		assertThat(ReflectionTestUtils.getField(sessionTemplateConverter, "instantiators"))
+				.isSameAs(ReflectionTestUtils.getField(source, "instantiators"));
 	}
 
 	@Test // DATAMONGO-1920