From 9d8fe97de0179e221836891e3a0baf8b7e264b5a Mon Sep 17 00:00:00 2001
From: Rob Bygrave <robin.bygrave@gmail.com>
Date: Thu, 7 Nov 2013 23:58:15 +1300
Subject: [PATCH] Adjusted Fix for Issue 56 - Using findIterate with MySQL
 streams the entire result set at once.  This makes the fix specific to the
 DatabasePlatform and findIterate() or findVisit().

---
 .../config/dbplatform/DatabasePlatform.java   | 24 +++++++++++++++++++
 .../config/dbplatform/MySqlPlatform.java      |  1 +
 .../ebeaninternal/server/query/CQuery.java    | 11 +++++----
 .../server/query/CQueryEngine.java            |  5 +++-
 4 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/src/main/java/com/avaje/ebean/config/dbplatform/DatabasePlatform.java b/src/main/java/com/avaje/ebean/config/dbplatform/DatabasePlatform.java
index 4ebad2729..54073bd84 100644
--- a/src/main/java/com/avaje/ebean/config/dbplatform/DatabasePlatform.java
+++ b/src/main/java/com/avaje/ebean/config/dbplatform/DatabasePlatform.java
@@ -63,6 +63,12 @@ public class DatabasePlatform {
 
   protected boolean selectCountWithAlias;
 
+  /**
+   * If set then use the FORWARD ONLY hint when creating ResultSets for
+   * findIterate() and findVisit().
+   */
+  protected boolean forwardOnlyHintOnFindIterate;
+  
   /**
    * Instantiates a new database platform.
    */
@@ -199,6 +205,24 @@ public class DatabasePlatform {
     return idInExpandedForm;
   }
 
+  /**
+   * Return true if the ResultSet TYPE_FORWARD_ONLY Hint should be used on
+   * findIterate() and findVisit() PreparedStatements.
+   * <p>
+   * This specifically is required for MySql when processing large results.
+   * </p>
+   */
+  public boolean isForwardOnlyHintOnFindIterate() {
+    return forwardOnlyHintOnFindIterate;
+  }
+
+  /**
+   * Set to true if the ResultSet TYPE_FORWARD_ONLY Hint should be used by default on findIterate PreparedStatements.
+   */
+  public void setForwardOnlyHintOnFindIterate(boolean forwardOnlyHintOnFindIterate) {
+    this.forwardOnlyHintOnFindIterate = forwardOnlyHintOnFindIterate;
+  }
+
   /**
    * Return the DB identity/sequence features for this platform.
    * 
diff --git a/src/main/java/com/avaje/ebean/config/dbplatform/MySqlPlatform.java b/src/main/java/com/avaje/ebean/config/dbplatform/MySqlPlatform.java
index fba60277e..c89f06a6e 100644
--- a/src/main/java/com/avaje/ebean/config/dbplatform/MySqlPlatform.java
+++ b/src/main/java/com/avaje/ebean/config/dbplatform/MySqlPlatform.java
@@ -31,6 +31,7 @@ public class MySqlPlatform extends DatabasePlatform {
     this.openQuote = "`";
     this.closeQuote = "`";
 
+    this.forwardOnlyHintOnFindIterate = true;
     this.booleanDbType = Types.BIT;
 
     dbTypeMap.put(Types.BIT, new DbType("tinyint(1) default 0"));
diff --git a/src/main/java/com/avaje/ebeaninternal/server/query/CQuery.java b/src/main/java/com/avaje/ebeaninternal/server/query/CQuery.java
index 0ad5c619c..40ab36f72 100644
--- a/src/main/java/com/avaje/ebeaninternal/server/query/CQuery.java
+++ b/src/main/java/com/avaje/ebeaninternal/server/query/CQuery.java
@@ -346,8 +346,8 @@ public class CQuery<T> implements DbReadContext, CancelableQuery {
   /**
    * Prepare bind and execute query with Forward only hints.
    */
-  public boolean prepareBindExecuteQueryForwardOnly() throws SQLException {
-    return prepareBindExecuteQueryWithOption(true);
+  public boolean prepareBindExecuteQueryForwardOnly(boolean dbPlatformForwardOnlyHint) throws SQLException {
+    return prepareBindExecuteQueryWithOption(dbPlatformForwardOnlyHint);
   }
 
   /**
@@ -357,7 +357,7 @@ public class CQuery<T> implements DbReadContext, CancelableQuery {
     return prepareBindExecuteQueryWithOption(false);
   }
 
-  private boolean prepareBindExecuteQueryWithOption(boolean forward) throws SQLException {
+  private boolean prepareBindExecuteQueryWithOption(boolean forwardOnlyHint) throws SQLException {
 
     synchronized (this) {
       if (cancelled || query.isCancelled()) {
@@ -371,8 +371,9 @@ public class CQuery<T> implements DbReadContext, CancelableQuery {
       // prepare
       SpiTransaction t = request.getTransaction();
       Connection conn = t.getInternalConnection();
-      if (forward) {
-        // Hints required for mysql for large resultset processing (Issue 56)
+            
+      if (forwardOnlyHint) {
+        // Use forward only hints for large resultset processing (Issue 56, MySql specific)
         pstmt = conn.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
       } else {
         pstmt = conn.prepareStatement(sql);        
diff --git a/src/main/java/com/avaje/ebeaninternal/server/query/CQueryEngine.java b/src/main/java/com/avaje/ebeaninternal/server/query/CQueryEngine.java
index 844f26af9..55757bb29 100644
--- a/src/main/java/com/avaje/ebeaninternal/server/query/CQueryEngine.java
+++ b/src/main/java/com/avaje/ebeaninternal/server/query/CQueryEngine.java
@@ -25,6 +25,8 @@ public class CQueryEngine {
 
   private static final Logger logger = LoggerFactory.getLogger(CQueryEngine.class);
 
+  private final DatabasePlatform dbPlatform;
+  
   private final CQueryBuilder queryBuilder;
 
   private final BackgroundExecutor backgroundExecutor;
@@ -33,6 +35,7 @@ public class CQueryEngine {
 
   public CQueryEngine(DatabasePlatform dbPlatform, Binder binder, BackgroundExecutor backgroundExecutor) {
 
+    this.dbPlatform = dbPlatform;
     this.backgroundExecutor = backgroundExecutor;
     this.queryBuilder = new CQueryBuilder(backgroundExecutor, dbPlatform, binder);
   }
@@ -122,7 +125,7 @@ public class CQueryEngine {
 
     try {
 
-      if (!cquery.prepareBindExecuteQueryForwardOnly()) {
+      if (!cquery.prepareBindExecuteQueryForwardOnly(dbPlatform.isForwardOnlyHintOnFindIterate())) {
         // query has been cancelled already
         logger.trace("Future fetch already cancelled");
         return null;