How to Save Port Constraints to a GraphML File

When saving a graph to a GraphML file, by default PortConstraints are not stored in this file.

Nevertheless, the integrated GraphML support (for yFiles 2.7 and higher) as well as the GraphML package already provide input and output handlers that can easily be registered to the GraphMLIOHandler as follows:

If you are using the integrated GraphML support for yFiles for Java 2.7 and higher:

y.io.GraphMLIOHandler ioh = new y.io.GraphMLIOHandler();

ioh.getGraphMLHandler().addInputHandlerProvider(new InputHandlerProvider() {
 public void onQueryInputHandler(QueryInputHandlersEvent event) throws GraphMLParseException {
   Element keyDefinition = event.getKeyDefinition();
   PortConstraintInputHandler handler = new PortConstraintInputHandler();

   //If we have encountered a graphml attribute that defines port constraints: 
   if (handler.acceptKey(keyDefinition)) {
     //Create the data providers if they don't exist yet
     initDataProvider(PortConstraintKeys.SOURCE_GROUPID_KEY, event.getContext().getGraph());
     initDataProvider(PortConstraintKeys.TARGET_GROUPID_KEY, event.getContext().getGraph());
     initDataProvider(PortConstraintKeys.SOURCE_PORT_CONSTRAINT_KEY, event.getContext().getGraph());
     initDataProvider(PortConstraintKeys.TARGET_PORT_CONSTRAINT_KEY, event.getContext().getGraph());
     //Actually register the input handler for the port constraint data
     event.addInputHandler(handler);
   }
 }

 private void initDataProvider(Object key, Graph graph) {
   DataProvider dp = graph.getDataProvider(key);
   if (dp == null || !(dp instanceof EdgeMap)) {
     dp = Maps.createEdgeMap(new WeakHashMap());
     graph.addDataProvider(key, dp);
   }
 }
});

ioh.getGraphMLHandler().addOutputHandlerProvider(new OutputHandlerProvider() {
  public void onQueryOutputHandler(QueryOutputHandlersEvent event) throws GraphMLWriteException {
    boolean isRegistered = false;
    Graph g = event.getContext().getGraph();
    Object[] keys = g.getDataProviderKeys();
    for (int i = 0; i < keys.length; i++) {
      Object key = keys[i];
      //Check if any of the port constraint relevant dataproviders is registered
      if(PortConstraintKeys.SOURCE_GROUPID_KEY.equals(key)  ||
         PortConstraintKeys.TARGET_GROUPID_KEY.equals(key) ||
         PortConstraintKeys.SOURCE_PORT_CONSTRAINT_KEY.equals(key) ||
         PortConstraintKeys.TARGET_PORT_CONSTRAINT_KEY.equals(key)) {
        isRegistered = true;
        break;
       }
    }
    if (isRegistered) {
      //Only use the output handler if the data providers exist
      event.addOutputHandler(new PortConstraintOutputHandler(), KeyScope.EDGE);
    }
  }
});

Using this GraphMLIOHandler will now guarantee that set PortConstraints will be stored and reloaded.

If you are using the GraphML extension package for yFiles for Java:

GraphMLIOHandler ioh = new GraphMLIOHandler();
//yext.graphml.graph2D.PortConstraintInputHandler
ioh.addInputHandler( new PortConstraintInputHandler());
//yext.graphml.graph2D.PortConstraintOutputHandler
ioh.addOutputHandler(new PortConstraintOutputHandler(), GraphMLConstants.SCOPE_EDGE);

Using this GraphMLIOHandler will now guarantee that set PortConstraints will be stored and reloaded.