From 9080a307ba0243648229e3778fe900a3493214ad Mon Sep 17 00:00:00 2001
From: Rich DiCroce <Rich.DiCroce@scientificgames.com>
Date: Thu, 5 Jul 2018 16:10:08 -0400
Subject: [PATCH 1/2] Fix bugs when using a cursor with EclipseLink:

- Some environments (e.g. WildFly) wrap the Query, causing the
instanceof check to fail, which prevents a cursor from being used. Fix
this by unwrapping the Query first.

- Telling EclipseLink to use a scrollable cursor, then telling it to use
a result set type of FORWARD_ONLY, makes no sense and causes the SQL
Server JDBC driver to throw an exception. Fix this by using a regular
CursoredStream instead.

- The original code never tells EclipseLink to release objects, causing
any benefit from using a cursor to be lost since all objects are
retained until the cursor is closed. Fix this by releasing objects after
completing each page.
---
 .../com/querydsl/jpa/EclipseLinkHandler.java  | 35 +++++++++++++++----
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java b/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java
index 93978a50f..cf6e95956 100644
--- a/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java
+++ b/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java
@@ -17,10 +17,11 @@ import java.io.Closeable;
 import java.io.IOException;
 import java.util.Iterator;
 
+import javax.persistence.PersistenceException;
 import javax.persistence.Query;
 
+import org.eclipse.persistence.config.HintValues;
 import org.eclipse.persistence.config.QueryHints;
-import org.eclipse.persistence.config.ResultSetType;
 import org.eclipse.persistence.jpa.JpaQuery;
 import org.eclipse.persistence.queries.Cursor;
 
@@ -54,20 +55,40 @@ class EclipseLinkHandler implements QueryHandler {
     @SuppressWarnings("unchecked")
     @Override
     public <T> CloseableIterator<T> iterate(Query query, FactoryExpression<?> projection) {
+        boolean canUseCursor = false;
+        try {
+            canUseCursor = query.unwrap(Query.class) instanceof JpaQuery;
+        } catch (PersistenceException e) {} // can't unwrap, just ignore the exception
+
         Iterator<T> iterator = null;
         Closeable closeable = null;
-        if (query instanceof JpaQuery) {
-            JpaQuery<T> elQuery = (JpaQuery<T>) query;
-            elQuery.setHint(QueryHints.RESULT_SET_TYPE, ResultSetType.ForwardOnly);
-            elQuery.setHint(QueryHints.SCROLLABLE_CURSOR, true);
-            final Cursor cursor = elQuery.getResultCursor();
+        if (canUseCursor) {
+            query.setHint(QueryHints.CURSOR, HintValues.TRUE);
+            final Cursor cursor = (Cursor) query.getSingleResult();
+            final int pageSize = cursor.getPageSize();
             closeable = new Closeable() {
                 @Override
                 public void close() throws IOException {
                     cursor.close();
                 }
             };
-            iterator = cursor;
+            iterator = new Iterator<T>() {
+                private int rowsSinceLastClear = 0;
+                
+                @Override
+                public boolean hasNext() {
+                    return cursor.hasNext();
+                }
+
+                @Override
+                public T next() {
+                    if (rowsSinceLastClear++ == pageSize) {
+                        rowsSinceLastClear = 0;
+                        cursor.clear();
+                    }
+                    return (T) cursor.next();
+                }
+            };
         } else {
             iterator = query.getResultList().iterator();
         }

From 18b0920c47666a761be1989271029e97f24827b7 Mon Sep 17 00:00:00 2001
From: Rich DiCroce <Rich.DiCroce@scientificgames.com>
Date: Fri, 6 Jul 2018 08:41:52 -0400
Subject: [PATCH 2/2] Fix checkstyle errors

---
 .../src/main/java/com/querydsl/jpa/EclipseLinkHandler.java    | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java b/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java
index cf6e95956..30f344edd 100644
--- a/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java
+++ b/querydsl-jpa/src/main/java/com/querydsl/jpa/EclipseLinkHandler.java
@@ -58,7 +58,7 @@ class EclipseLinkHandler implements QueryHandler {
         boolean canUseCursor = false;
         try {
             canUseCursor = query.unwrap(Query.class) instanceof JpaQuery;
-        } catch (PersistenceException e) {} // can't unwrap, just ignore the exception
+        } catch (PersistenceException e) { } // can't unwrap, just ignore the exception
 
         Iterator<T> iterator = null;
         Closeable closeable = null;
@@ -74,7 +74,7 @@ class EclipseLinkHandler implements QueryHandler {
             };
             iterator = new Iterator<T>() {
                 private int rowsSinceLastClear = 0;
-                
+
                 @Override
                 public boolean hasNext() {
                     return cursor.hasNext();