code: func (g *Graph) AddVolumeAttachment(attachmentName, nodeName string) {
  	g.lock.Lock()
  	defer g.lock.Unlock()
  
  	// clear existing edges
  	g.deleteVertex_locked(vaVertexType, "", attachmentName)
  
  	// if we have a node, establish new edges
  	if len(nodeName) > 0 {
  		vaVertex := g.getOrCreateVertex_locked(vaVertexType, "", attachmentName)
  		nodeVertex := g.getOrCreateVertex_locked(nodeVertexType, "", nodeName)
  		g.graph.SetEdge(newDestinationEdge(vaVertex, nodeVertex, nodeVertex))
  	}
  }
docs: // AddVolumeAttachment sets up edges for the following relationships:
  //
  //   volume attachment -> node