code: public Node createProxyNode(Object sourceNodeId, Object targetNodeId, GraphDatabaseService graphDb,
              EntityMetadata sourceEntityMetadata, EntityMetadata targetEntityMetadata)
      {
  
          String sourceNodeIdColumnName = ((AbstractAttribute) sourceEntityMetadata.getIdAttribute()).getJPAColumnName();
          String targetNodeIdColumnName = ((AbstractAttribute) targetEntityMetadata.getIdAttribute()).getJPAColumnName();
  
          Node node = graphDb.createNode();
          node.setProperty(PROXY_NODE_TYPE_KEY, PROXY_NODE_VALUE);
          node.setProperty(sourceNodeIdColumnName, sourceNodeId);
          node.setProperty(targetNodeIdColumnName, targetNodeId);
          return node;
      }
docs: Create "Proxy" nodes into Neo4J. Proxy nodes are defined as nodes in
  Neo4J that refer to a record in some other database. They cater to
  polyglot persistence cases.