Provide for a layer comment to be made available for vector layers

For postgres provider, get the layer comment from the table comment (if
it exists). Resolves ticket #244


git-svn-id: http://svn.osgeo.org/qgis/trunk@6726 c8812cc2-4d05-0410-92ff-de0c093fc19c

src/app/qgsvectorlayerproperties.cpp

@@ -380,6 +380,15 @@ QString QgsVectorLayerProperties::getMetadata()
   myMetadataQString += tr("General:");
   myMetadataQString += "</td></tr>";
 
+  // data comment
+  if (!(layer->dataComment().isEmpty()))
+  {
+    myMetadataQString += "<tr><td bgcolor=\"white\">";
+    myMetadataQString += tr("Layer comment: ") + 
+        layer->dataComment();
+    myMetadataQString += "</td></tr>";
+  }
+
   //storage type
   myMetadataQString += "<tr><td bgcolor=\"white\">";
   myMetadataQString += tr("Storage type of this layer : ") + 

src/core/qgsvectordataprovider.cpp

@@ -59,6 +59,10 @@ void QgsVectorDataProvider::getFeatureGeometry(int key, QgsFeature *f)
 {
 }
 
+QString QgsVectorDataProvider::dataComment() const
+{
+    return QString();
+}
 
 bool QgsVectorDataProvider::addFeatures(QgsFeatureList & flist)
 {

src/core/qgsvectordataprovider.h

@@ -155,6 +155,12 @@ class CORE_EXPORT QgsVectorDataProvider : public QgsDataProvider
        */
       virtual const QgsFieldMap & fields() const = 0;
 
+      /**
+       * Return a short comment for the data that this provider is
+       * providing access to (e.g. the comment for postgres table).
+       */
+      virtual QString dataComment() const;
+
       /** 
        * Reset the layer to clear any spatial filtering or other contstraints that
        * would prevent the entire record set from being traversed by call to 

src/core/qgsvectorlayer.cpp

@@ -165,6 +165,15 @@ QString QgsVectorLayer::capabilitiesString() const
   return 0;
 }
 
+QString QgsVectorLayer::dataComment() const
+{
+  if (mDataProvider)
+  {
+    return mDataProvider->dataComment();
+  }
+  return QString();
+}
+
 
 QString QgsVectorLayer::providerType() const
 {

src/core/qgsvectorlayer.h

@@ -82,6 +82,9 @@ public:
   /** Capabilities for this layer in a friendly format. */
   QString capabilitiesString() const;
 
+  /** Returns a comment for the data in the layer */
+  QString dataComment() const;
+
   /** Set the primary display field to be used in the identify results dialog */
   void setDisplayField(QString fldName=0);
 

src/providers/postgres/qgspostgresprovider.cpp

@@ -176,17 +176,13 @@ QgsPostgresProvider::QgsPostgresProvider(QString const & uri)
       QString tableoid = PQgetvalue(tresult, 0, 0);
       PQclear(tresult);
 
-/* Code to extrac the table description. Needs a way to make is accesssible
-to the rest of qgis...
-
       // Get the table description
       sql = "SELECT description FROM pg_description WHERE "
-          "classoid = " + tableoid + " AND objsubid = 0";
+          "objoid = " + tableoid + " AND objsubid = 0";
       tresult = PQexec(pd, (const char*) sql.utf8());
       if (PQntuples(tresult) > 0)
-        mDescription = PQgetvalue(tresult, 0, 0);
+        mDataComment = PQgetvalue(tresult, 0, 0);
       PQclear(tresult);
-*/
 
       // Populate the field vector for this layer. The field vector contains
       // field name, type, length, and precision (if numeric)
@@ -685,6 +681,11 @@ const QgsFieldMap & QgsPostgresProvider::fields() const
   return attributeFields;
 }
 
+QString QgsPostgresProvider::dataComment() const
+{
+  return mDataComment;
+}
+
 void QgsPostgresProvider::reset()
 {
   // reset the cursor to the first record

src/providers/postgres/qgspostgresprovider.h

@@ -185,6 +185,12 @@ class QgsPostgresProvider:public QgsVectorDataProvider
      */
     const QgsFieldMap & fields() const;
 
+    /**
+     * Return a short comment for the data that this provider is
+     * providing access to (e.g. the comment for postgres table).
+     */
+    QString dataComment() const;
+
     /** Reset the layer - for a PostgreSQL layer, this means clearing the PQresult
      * pointer and setting it to 0
      */
@@ -335,6 +341,7 @@ class QgsPostgresProvider:public QgsVectorDataProvider
     std::vector < QgsFeature > features;
     QgsFieldMap attributeFields;
     std::map < int, int > attributeFieldsIdMap;
+    QString mDataComment;
 
     //! Data source URI struct for this layer
     QgsDataSourceURI mUri;