Ensure related entities are eagerly loaded

pom.xml

@@ -64,7 +64,7 @@
 
 		<spring.version>4.2.0.RELEASE</spring.version>
 		<spring.data.jpa.version>1.8.2.RELEASE</spring.data.jpa.version>
-		<hibernate.version>4.3.10.Final</hibernate.version>
+		<hibernate.version>4.3.11.Final</hibernate.version>
 		<hibernate.validator.version>5.2.0.Final</hibernate.validator.version>
 		<jackson.version>2.6.0</jackson.version>
 		<javax.el.api.version>2.2.5</javax.el.api.version>

src/main/java/org/springframework/data/jpa/datatables/repository/DataTablesUtils.java

@@ -7,6 +7,7 @@
 import javax.persistence.criteria.CriteriaBuilder;
 import javax.persistence.criteria.CriteriaQuery;
 import javax.persistence.criteria.Expression;
+import javax.persistence.criteria.Fetch;
 import javax.persistence.criteria.From;
 import javax.persistence.criteria.JoinType;
 import javax.persistence.criteria.Predicate;
@@ -102,6 +103,29 @@ public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
           }
           predicate = criteriaBuilder.and(predicate, matchOneColumnPredicate);
         }
+        // findAll method does a count query first, and then query for the actual data. Yet in the
+        // count query, adding a JOIN FETCH results in the following error 'query specified join
+        // fetching, but the owner of the fetched association was not present in the select list'
+        // see https://jira.spring.io/browse/DATAJPA-105
+        boolean isCountQuery = query.getResultType() == Long.class;
+        if (isCountQuery) {
+          return predicate;
+        }
+        // add JOIN FETCH when necessary
+        for (ColumnParameter column : input.getColumns()) {
+          if (!column.getSearchable() || !column.getData().contains(ATTRIBUTE_SEPARATOR)) {
+            continue;
+          }
+          String[] values = column.getData().split("\\" + ATTRIBUTE_SEPARATOR);
+          if (root.getModel().getAttribute(values[0])
+              .getPersistentAttributeType() == PersistentAttributeType.EMBEDDED) {
+            continue;
+          }
+          Fetch<?, ?> fetch = null;
+          for (int i = 0; i < values.length - 1; i++) {
+            fetch = (fetch == null ? root : fetch).fetch(values[i], JoinType.LEFT);
+          }
+        }
         return predicate;
       }
 

src/test/java/org/springframework/data/jpa/datatables/Config.java

@@ -5,7 +5,9 @@
 
 import javax.sql.DataSource;
 
+import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Environment;
+import org.hibernate.jpa.HibernateEntityManagerFactory;
 import org.hibernate.tool.hbm2ddl.MultipleLinesSqlCommandExtractor;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -60,4 +62,10 @@ public AbstractEntityManagerFactoryBean entityManagerFactory() throws SQLExcepti
 
     return bean;
   }
+
+  @Bean
+  public SessionFactory sessionFactory() throws SQLException {
+    return ((HibernateEntityManagerFactory) entityManagerFactory().getObject()).getSessionFactory();
+  }
+
 }

src/test/java/org/springframework/data/jpa/datatables/repository/LessonRepositoryTest.java

@@ -4,6 +4,8 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 
+import org.hibernate.SessionFactory;
+import org.hibernate.stat.Statistics;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -22,6 +24,9 @@ public class LessonRepositoryTest {
   @Autowired
   private LessonRepository lessonRepository;
 
+  @Autowired
+  private SessionFactory sessionFactory;
+
   @Test
   public void testThroughTwoManyToOneRelationships() {
     DataTablesInput input = getBasicInput();
@@ -41,6 +46,22 @@ public void testThroughTwoManyToOneRelationships() {
     assertEquals(7, output.getRecordsTotal());
   }
 
+  @Test
+  public void testEagerLoading() {
+    DataTablesInput input = getBasicInput();
+
+    Statistics statistics = sessionFactory.getStatistics();
+    statistics.setStatisticsEnabled(true);
+    DataTablesOutput<Lesson> output = lessonRepository.findAll(input);
+    assertEquals("CourseTypeA", output.getData().get(0).getCourse().getType().getName());
+    statistics.setStatisticsEnabled(false);
+
+    // there should be only three executed queries : count unfiltered, count filtered and actual
+    // data (with FETCH JOIN)
+    assertEquals(3, statistics.getPrepareStatementCount());
+    assertEquals(7 + 3 + 2, statistics.getEntityLoadCount());
+  }
+
   /**
    * 
    * @return basic input parameters

src/test/resources/log4j.properties

@@ -4,4 +4,5 @@ log4j.appender.console.layout=org.apache.log4j.PatternLayout
 log4j.appender.console.layout.ConversionPattern=%d{ABSOLUTE} %5p %40.40c:%4L - %m%n
 log4j.appender.console=org.apache.log4j.ConsoleAppender
 
-log4j.logger.org.springframework=INFO
+log4j.logger.org.springframework=INFO
+log4j.logger.org.hibernate.SQL=DEBUG