From 9df99f02f5445379bca7a31ca665c977acb3f984 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timo=20Westk=C3=A4mper?= <timo.westkamper@gmail.com>
Date: Fri, 18 Jul 2014 08:14:40 +0300
Subject: [PATCH] Improve limit/offset handling

---
 .../query/sql/SQLServer2012Templates.java     | 37 +++++++++++++++----
 .../query/sql/SQLServer2012TemplatesTest.java | 12 +++---
 2 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/querydsl-sql/src/main/java/com/mysema/query/sql/SQLServer2012Templates.java b/querydsl-sql/src/main/java/com/mysema/query/sql/SQLServer2012Templates.java
index bf371e96d..fd4e79827 100644
--- a/querydsl-sql/src/main/java/com/mysema/query/sql/SQLServer2012Templates.java
+++ b/querydsl-sql/src/main/java/com/mysema/query/sql/SQLServer2012Templates.java
@@ -13,9 +13,11 @@
  */
 package com.mysema.query.sql;
 
+import com.mysema.query.QueryFlag;
 import com.mysema.query.QueryFlag.Position;
 import com.mysema.query.QueryMetadata;
 import com.mysema.query.QueryModifiers;
+import com.mysema.query.support.Expressions;
 
 /**
  * SQLServer2012Templates is an SQL dialect for Microsoft SQL Server 2012 and later
@@ -25,6 +27,8 @@ import com.mysema.query.QueryModifiers;
  */
 public class SQLServer2012Templates extends SQLServerTemplates {
 
+    private String topTemplate = "top {0s} ";
+
     private String limitOffsetTemplate = "\noffset {1} rows fetch next {0} rows only";
 
     private String offsetTemplate = "\noffset {0} rows";
@@ -52,7 +56,22 @@ public class SQLServer2012Templates extends SQLServerTemplates {
 
     @Override
     public void serialize(QueryMetadata metadata, boolean forCountRow, SQLSerializer context) {
-        context.serializeForQuery(metadata, forCountRow);
+        if (!forCountRow && metadata.getModifiers().isRestricting() && metadata.getOrderBy().isEmpty()
+                && !metadata.getJoins().isEmpty()) {
+            QueryModifiers mod = metadata.getModifiers();
+            // use top if order by is empty
+            if (mod.getOffset() == null) {
+                // select top ...
+                metadata = metadata.clone();
+                metadata.addFlag(new QueryFlag(QueryFlag.Position.AFTER_SELECT,
+                        Expressions.template(Integer.class, topTemplate, mod.getLimit())));
+                context.serializeForQuery(metadata, forCountRow);
+            } else {
+                throw new IllegalStateException("offset not supported without order by");
+            }
+        } else {
+            context.serializeForQuery(metadata, forCountRow);
+        }
 
         if (!metadata.getFlags().isEmpty()) {
             context.serialize(Position.END, metadata.getFlags());
@@ -61,13 +80,15 @@ public class SQLServer2012Templates extends SQLServerTemplates {
 
     @Override
     protected void serializeModifiers(QueryMetadata metadata, SQLSerializer context) {
-        QueryModifiers mod = metadata.getModifiers();
-        if (mod.getLimit() == null) {
-            context.handle(offsetTemplate, mod.getOffset());
-        } else if (mod.getOffset() == null) {
-            context.handle(limitOffsetTemplate, mod.getLimit(), 0);
-        } else {
-            context.handle(limitOffsetTemplate, mod.getLimit(), mod.getOffset());
+        if (!metadata.getOrderBy().isEmpty()) {
+            QueryModifiers mod = metadata.getModifiers();
+            if (mod.getLimit() == null) {
+                context.handle(offsetTemplate, mod.getOffset());
+            } else if (mod.getOffset() == null) {
+                context.handle(limitOffsetTemplate, mod.getLimit(), 0);
+            } else {
+                context.handle(limitOffsetTemplate, mod.getLimit(), mod.getOffset());
+            }
         }
     }
 
diff --git a/querydsl-sql/src/test/java/com/mysema/query/sql/SQLServer2012TemplatesTest.java b/querydsl-sql/src/test/java/com/mysema/query/sql/SQLServer2012TemplatesTest.java
index dc3bc203c..0f938e3ba 100644
--- a/querydsl-sql/src/test/java/com/mysema/query/sql/SQLServer2012TemplatesTest.java
+++ b/querydsl-sql/src/test/java/com/mysema/query/sql/SQLServer2012TemplatesTest.java
@@ -13,10 +13,6 @@
  */
 package com.mysema.query.sql;
 
-import static org.junit.Assert.assertEquals;
-
-import org.junit.Test;
-
 import com.mysema.query.types.ConstantImpl;
 import com.mysema.query.types.Operation;
 import com.mysema.query.types.OperationImpl;
@@ -24,6 +20,8 @@ import com.mysema.query.types.Path;
 import com.mysema.query.types.expr.NumberExpression;
 import com.mysema.query.types.path.SimplePath;
 import com.mysema.query.types.template.NumberTemplate;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
 
 
 public class SQLServer2012TemplatesTest extends AbstractSQLTemplatesTest {
@@ -64,14 +62,14 @@ public class SQLServer2012TemplatesTest extends AbstractSQLTemplatesTest {
     public void Limit() {
         query.from(survey1).limit(5);
         query.getMetadata().addProjection(survey1.id);
-        assertEquals("select survey1.ID from SURVEY survey1 offset ? rows fetch next ? rows only", query.toString());
+        assertEquals("select top 5 survey1.ID from SURVEY survey1", query.toString());
     }
 
     @Test
     public void Modifiers() {
-        query.from(survey1).limit(5).offset(3);
+        query.from(survey1).limit(5).offset(3).orderBy(survey1.id.asc());
         query.getMetadata().addProjection(survey1.id);
-        assertEquals("select survey1.ID from SURVEY survey1 offset ? rows fetch next ? rows only", query.toString());
+        assertEquals("select survey1.ID from SURVEY survey1 order by survey1.ID asc offset ? rows fetch next ? rows only", query.toString());
     }
 
     @Test