DATAREST-500 - Enable lazy-loading proxy resolution on Hibernate 4 module.

We now explicitly activate the resolution of lazy-loading proxies on Hibernate 4 to make sure not already populated lazy-loading proxies are actively resolved.

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/Jackson2DatatypeHelper.java

@@ -62,7 +62,11 @@ public class Jackson2DatatypeHelper {
 	private static class Hibernate4ModuleRegistrar {
 
 		public static void registerModule(ObjectMapper mapper) {
-			mapper.registerModule(new Hibernate4Module());
+
+			Hibernate4Module module = new Hibernate4Module();
+			module.enable(Hibernate4Module.Feature.FORCE_LAZY_LOADING);
+
+			mapper.registerModule(module);
 		}
 	}
 

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/Jackson2DatatypeHelperIntegrationTests.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2015 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
+ *
+ *      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 org.springframework.data.rest.webmvc.json;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import javax.persistence.EntityManager;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.mapping.PersistentProperty;
+import org.springframework.data.mapping.PersistentPropertyAccessor;
+import org.springframework.data.mapping.context.PersistentEntities;
+import org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration;
+import org.springframework.data.rest.webmvc.jpa.Order;
+import org.springframework.data.rest.webmvc.jpa.OrderRepository;
+import org.springframework.data.rest.webmvc.jpa.Person;
+import org.springframework.data.rest.webmvc.jpa.PersonRepository;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.transaction.annotation.Transactional;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+/**
+ * Integration tests for {@link Jackson2DatatypeHelper}.
+ * 
+ * @author Oliver Gierke
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = { RepositoryTestsConfig.class, RepositoryRestMvcConfiguration.class })
+@Transactional
+public class Jackson2DatatypeHelperIntegrationTests {
+
+	@Autowired PersistentEntities entities;
+	@Autowired ObjectMapper objectMapper;
+
+	@Autowired PersonRepository people;
+	@Autowired OrderRepository orders;
+	@Autowired EntityManager em;
+
+	Order order;
+
+	@Before
+	public void setUp() {
+
+		this.order = orders.save(new Order(people.save(new Person("Dave", "Matthews"))));
+
+		// Reset JPA to make sure the query returns a result with proxy references
+		em.flush();
+		em.clear();
+	}
+
+	/**
+	 * @see DATAREST-500
+	 */
+	@Test
+	public void configuresHIbernate4ModuleToLoadLazyLoadingProxies() throws Exception {
+
+		PersistentEntity<?, ?> entity = entities.getPersistentEntity(Order.class);
+		PersistentProperty<?> property = entity.getPersistentProperty("creator");
+		PersistentPropertyAccessor accessor = entity.getPropertyAccessor(orders.findOne(this.order.getId()));
+
+		assertThat(objectMapper.writeValueAsString(accessor.getProperty(property)), is(not("null")));
+	}
+}