Applied bugfix patch from Stefanie Tellex:

 - The bug  occurs when you make two providers that 
   access the same table, and then try to iterate 
   through the features in each provider in a nested loop.
 - The provider in the inner loop would never have any 
   features because all providers use the same cursor 
   name so things would get messed up.
 - This patch fixes the bug by adding a providerId 
   member to QgsPostgresProvider, and appending the 
   id to all cursor names.


git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@8092 c8812cc2-4d05-0410-92ff-de0c093fc19c

src/providers/postgres/qgspostgresprovider.cpp

@@ -57,14 +57,17 @@
 
 const QString POSTGRES_KEY = "postgres";
 const QString POSTGRES_DESCRIPTION = "PostgreSQL/PostGIS data provider";
-
+int QgsPostgresProvider::providerIds = 0;
 
   QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
 : QgsVectorDataProvider(uri),
   geomType(QGis::WKBUnknown),
   mFeatureQueueSize(200),
   gotPostgisVersion(FALSE)
 {
+
+  providerId = QString("%1").arg(providerIds++);
+
   // assume this is a valid layer until we determine otherwise
   valid = true;
   /* OPEN LOG FILE */
@@ -330,7 +333,7 @@ bool QgsPostgresProvider::getNextFeature(QgsFeature& feature)
     // Top up our queue if it is empty
     if (mFeatureQueue.empty())
     {
-      QString fetch = QString("fetch forward %1 from qgisf")
+      QString fetch = QString("fetch forward %1 from qgisf" + providerId)
         .arg(mFeatureQueueSize);
 
       if(mFirstFetch)
@@ -472,7 +475,7 @@ void QgsPostgresProvider::select(QgsAttributeList fetchAttributes,
     }
   }
 
-  QString declare = "declare qgisf binary cursor for select \"" + primaryKey + "\"";
+  QString declare = "declare qgisf" + providerId + " binary cursor for select \"" + primaryKey + "\"";
 
   if(fetchGeometry)
   {
@@ -566,7 +569,7 @@ bool QgsPostgresProvider::getFeatureAtId(int featureId,
     }
   }
 
-  QString sql = "declare qgisfid binary cursor for select \"" + primaryKey + "\"";
+  QString sql = "declare qgisfid" + providerId + " binary cursor for select \"" + primaryKey + "\"";
 
   if(fetchGeometry)
   {
@@ -591,7 +594,7 @@ bool QgsPostgresProvider::getFeatureAtId(int featureId,
   // execute query
   PQexec(connection, (const char *)(sql.utf8()));
 
-  PGresult *res = PQexec(connection, "fetch forward 1 from qgisfid");
+  PGresult *res = PQexec(connection, "fetch forward 1 from qgisfid" + providerId);
 
   int rows = PQntuples(res);
   if (rows == 0)
@@ -712,7 +715,7 @@ QString QgsPostgresProvider::dataComment() const
 
 void QgsPostgresProvider::reset()
 {
-  QString move = "move 0 in qgisf"; //move cursor to first record
+  QString move = "move 0 in qgisf" + providerId; //move cursor to first record
   PQexec(connection, (const char *)(move.utf8()));
   mFeatureQueue.empty();
   loadFields();

src/providers/postgres/qgspostgresprovider.h

@@ -566,6 +566,8 @@ class QgsPostgresProvider:public QgsVectorDataProvider
     void disconnectDb();
 
     static QMap<QString, Conn *> connections;
+    static int providerIds;
+    QString providerId;
 };
 
 #endif