Prevent potential image overwrite in MySQL query result

4 files changed, 37 insertions, 8 deletions

diff --git a/odb/mysql/object-result.hxx b/odb/mysql/object-result.hxx
index 30d0eee..896fc9d 100644
--- a/odb/mysql/object-result.hxx
+++ b/odb/mysql/object-result.hxx
@@ -60,7 +60,7 @@ namespace odb
 
     private:
       void
-      fetch ();
+      fetch (bool next = true);
 
     private:
       details::shared_ptr<select_statement> statement_;
diff --git a/odb/mysql/object-result.txx b/odb/mysql/object-result.txx
index 502cb8c..1506d96 100644
--- a/odb/mysql/object-result.txx
+++ b/odb/mysql/object-result.txx
@@ -36,10 +36,17 @@ namespace odb
 
     template <typename T>
     void object_result_impl<T>::
-    load (object_type& obj, bool)
+    load (object_type& obj, bool f)
     {
       if (count_ > statement_->fetched ())
         fetch ();
+      else if (f && statement_->cached ())
+      {
+        // We have to re-load the image in case it has been overwritten
+        // between the last time we fetched and this call to load().
+        //
+        fetch (false);
+      }
 
       // This is a top-level call so the statements cannot be locked.
       //
@@ -79,6 +86,13 @@ namespace odb
     {
       if (count_ > statement_->fetched ())
         fetch ();
+      else if (statement_->cached ())
+      {
+        // We have to re-load the image in case it has been overwritten
+        // between the last time we fetched and this call to load_id().
+        //
+        fetch (false);
+      }
 
       return object_traits::id (statements_.image ());
     }
@@ -104,7 +118,7 @@ namespace odb
 
     template <typename T>
     void object_result_impl<T>::
-    fetch ()
+    fetch (bool next)
     {
       // If the result is cached, the image can grow between calls
       // to fetch() as a result of other statements execution.
@@ -122,9 +136,9 @@ namespace odb
         }
       }
 
-      while (!this->end_ && count_ > statement_->fetched ())
+      while (!this->end_ && (!next || count_ > statement_->fetched ()))
       {
-        select_statement::result r (statement_->fetch ());
+        select_statement::result r (statement_->fetch (next));
 
         switch (r)
         {
@@ -132,7 +146,7 @@ namespace odb
           {
             // Don't re-fetch data we are skipping.
             //
-            if (count_ != statement_->fetched ())
+            if (next && count_ != statement_->fetched ())
               continue;
 
             typename object_traits::image_type& im (statements_.image ());
@@ -161,6 +175,11 @@ namespace odb
             break;
           }
         }
+
+        // If we are refetching the current row, then we are done.
+        //
+        if (!next)
+          break;
       }
     }
 
diff --git a/odb/mysql/statement.cxx b/odb/mysql/statement.cxx
index 4cd6f35..d4e4943 100644
--- a/odb/mysql/statement.cxx
+++ b/odb/mysql/statement.cxx
@@ -146,7 +146,7 @@ namespace odb
     }
 
     select_statement::result select_statement::
-    fetch ()
+    fetch (bool next)
     {
       if (result_version_ != result_.version)
       {
@@ -163,6 +163,12 @@ namespace odb
         result_version_ = result_.version;
       }
 
+      if (!next && rows_ != 0)
+      {
+        assert (cached_);
+        mysql_stmt_data_seek (stmt_, static_cast<my_ulonglong> (rows_ - 1));
+      }
+
       int r (mysql_stmt_fetch (stmt_));
 
       switch (r)
diff --git a/odb/mysql/statement.hxx b/odb/mysql/statement.hxx
index ec128f2..93adea4 100644
--- a/odb/mysql/statement.hxx
+++ b/odb/mysql/statement.hxx
@@ -97,8 +97,12 @@ namespace odb
         return rows_;
       }
 
+      // Fetch next or current row depending on the next argument.
+      // Note that fetching of the current row is only supported
+      // if the result is cached.
+      //
       result
-      fetch ();
+      fetch (bool next = true);
 
       void
       refetch ();