Remember the position in a sorted query when fetching rows for a dymanic playlist

src/smartplaylists/querygenerator.cpp

@@ -24,13 +24,15 @@
 namespace smart_playlists {
 
 QueryGenerator::QueryGenerator()
-  : dynamic_(false)
+  : dynamic_(false),
+    current_pos_(0)
 {
 }
 
 void QueryGenerator::Load(const Search& search) {
   search_ = search;
   dynamic_ = false;
+  current_pos_ = 0;
 }
 
 void QueryGenerator::Load(const QByteArray& data) {
@@ -50,6 +52,7 @@ QByteArray QueryGenerator::Save() const {
 
 PlaylistItemList QueryGenerator::Generate() {
   previous_ids_.clear();
+  current_pos_ = 0;
   return GenerateMore(0);
 }
 
@@ -62,6 +65,11 @@ PlaylistItemList QueryGenerator::GenerateMore(int count) {
     search_copy.limit_ = kDynamicFuture;
   }
 
+  if (search_copy.sort_type_ != Search::Sort_Random) {
+    search_copy.first_item_ = current_pos_;
+    current_pos_ += search_copy.limit_;
+  }
+
   SongList songs = backend_->FindSongs(search_copy);
   PlaylistItemList items;
   foreach (const Song& song, songs) {

src/smartplaylists/querygenerator.h

@@ -45,6 +45,7 @@ private:
   bool dynamic_;
 
   QList<int> previous_ids_;
+  int current_pos_;
 };
 
 } // namespace

src/smartplaylists/search.cpp

@@ -33,7 +33,8 @@ Search::Search(
     terms_(terms),
     sort_type_(sort_type),
     sort_field_(sort_field),
-    limit_(limit)
+    limit_(limit),
+    first_item_(-1)
 {
 }
 
@@ -43,6 +44,7 @@ void Search::Reset() {
   sort_type_ = Sort_Random;
   sort_field_ = SearchTerm::Field_Title;
   limit_ = -1;
+  first_item_ = -1;
 }
 
 QString Search::ToSql(const QString& songs_table) const {
@@ -82,7 +84,9 @@ QString Search::ToSql(const QString& songs_table) const {
   }
 
   // Add limit
-  if (limit_ != -1) {
+  if (first_item_) {
+    sql += QString(" LIMIT %1,%2").arg(first_item_).arg(limit_);
+  } else if (limit_ != -1) {
     sql += " LIMIT " + QString::number(limit_);
   }
 

src/smartplaylists/search.h

@@ -56,7 +56,9 @@ public:
   SearchTerm::Field sort_field_;
   int limit_;
 
+  // Not persisted, used to alter the behaviour of the query
   QList<int> id_not_in_;
+  int first_item_;
 
   void Reset();
   QString ToSql(const QString& songs_table) const;