Postpone fetching of the data for cached results

This way if an object of the same type is loaded in between iteration, the fetched
image won't be messed up.

1 files changed, 68 insertions, 27 deletions

diff --git a/odb/mysql/result.txx b/odb/mysql/result.txx
index 4b18abc..e3ef10b 100644
--- a/odb/mysql/result.txx
+++ b/odb/mysql/result.txx
@@ -3,6 +3,7 @@
 // copyright : Copyright (c) 2009-2010 Code Synthesis Tools CC
 // license   : GNU GPL v2; see accompanying LICENSE file
 
+#include <odb/exceptions.hxx>
 #include <odb/cache-traits.hxx>
 
 namespace odb
@@ -21,15 +22,18 @@ namespace odb
                  object_statements<object_type>& statements)
         : odb::result_impl<T> (statements.connection ().database ()),
           statement_ (statement),
-          statements_ (statements)
+          statements_ (statements),
+          count_ (0)
     {
-      next ();
     }
 
     template <typename T>
     void result_impl<T>::
     load (object_type& obj)
     {
+      if (count_ > statement_->fetched ())
+        fetch ();
+
       // This is a top-level call so the statements cannot be locked.
       //
       assert (!statements_.locked ());
@@ -45,6 +49,9 @@ namespace odb
     typename result_impl<T>::id_type result_impl<T>::
     load_id ()
     {
+      if (count_ > statement_->fetched ())
+        fetch ();
+
       return object_traits::id (statements_.image ());
     }
 
@@ -54,8 +61,25 @@ namespace odb
     {
       this->current (pointer_type ());
 
-      // If the result was cached the image can grow between calls
-      // to next() as a result of other statements execution.
+      // If we are cached, simply increment the position and
+      // postpone the actual row fetching until later. This way
+      // if the same object is loaded in between iteration, the
+      // image won't be messed up.
+      //
+      count_++;
+
+      if (statement_->cached ())
+        this->end_ = count_ > statement_->result_size ();
+      else
+        fetch ();
+    }
+
+    template <typename T>
+    void result_impl<T>::
+    fetch ()
+    {
+      // If the result is cached, the image can grow between calls
+      // to fetch() as a result of other statements execution.
       //
       if (statement_->cached ())
       {
@@ -70,33 +94,41 @@ namespace odb
         }
       }
 
-      select_statement::result r (statement_->fetch ());
-
-      switch (r)
+      while (count_ > statement_->fetched ())
       {
-      case select_statement::truncated:
+        select_statement::result r (statement_->fetch ());
+
+        switch (r)
         {
-          typename object_traits::image_type& im (statements_.image ());
-          object_traits::grow (im, statements_.out_image_error ());
+        case select_statement::truncated:
+          {
+            // Don't re-fetch data we are skipping.
+            //
+            if (count_ != statement_->fetched ())
+              continue;
+
+            typename object_traits::image_type& im (statements_.image ());
+            object_traits::grow (im, statements_.out_image_error ());
 
-          if (im.version != statements_.out_image_version ())
+            if (im.version != statements_.out_image_version ())
+            {
+              binding& b (statements_.out_image_binding ());
+              object_traits::bind (b.bind, im, true);
+              statements_.out_image_version (im.version);
+              b.version++;
+              statement_->refetch ();
+            }
+            // Fall throught.
+          }
+        case select_statement::success:
           {
-            binding& b (statements_.out_image_binding ());
-            object_traits::bind (b.bind, im, true);
-            statements_.out_image_version (im.version);
-            b.version++;
-            statement_->refetch ();
+            break;
+          }
+        case select_statement::no_data:
+          {
+            this->end_ = true;
+            break;
           }
-          // Fall throught.
-        }
-      case select_statement::success:
-        {
-          break;
-        }
-      case select_statement::no_data:
-        {
-          this->end_ = true;
-          break;
         }
       }
     }
@@ -105,13 +137,22 @@ namespace odb
     void result_impl<T>::
     cache ()
     {
-      statement_->cache ();
+      if (!statement_->cached ())
+      {
+        statement_->cache ();
+
+        if (count_ >= statement_->result_size ())
+          this->end_ = true;
+      }
     }
 
     template <typename T>
     std::size_t result_impl<T>::
     size ()
     {
+      if (!statement_->cached ())
+        throw result_not_cached ();
+
       return statement_->result_size ();
     }
   }