背景：dagre可以在节点数据中配置layer字段，为节点指定层级，但layer的指定不能违背图结构与层次布局的原则，也就是说每一条边的起点的layer一定小于终点的layer值，否则会导致布局失败。

解决办法：动态添加节点，在需要增加同级节点的node处添加一个影子节点，隐藏该影子节点，将需要添加的节点动态添加到该影子节点上。

示例图：

代码如下：

import G6 from '@antv/g6';
import insertCss from 'insert-css';

insertCss(`
  .g6-tooltip {
    border-radius: 6px;
    font-size: 12px;
    color: #fff;
    background-color: #000;
    padding: 2px 8px;
    text-align: center;
  }
`);

const data = {
  nodes: [
    {
      id: '1',
      dataType: 'alps',
      name: '1',
      layer:0
    },
    {
      id: '2',
      dataType: 'alps',
      name: '2',
      layer:0
    },
    {
      id: '3',
      dataType: 'alps',
      name: '3',
      layer:1
    },
     {
      id: '6',
      dataType: 'sql2',
      name: '6',
      layer:3
    },
     {
      id: '7',
      dataType: 'sql2',
      name: '7',
      layer:3
    },
    
  ],
  edges: [
    {
      source: '2',
      target: '3',
    },
    {
      source: '1',
      target: '3',
    },
    {
      source: '3',
      target: '6',
    },
    {
      source: '3',
      target: '7',
    },

  ],
};

G6.registerNode(
  'sql',
  {
    drawShape(cfg, group) {
      const rect = group.addShape('rect', {
        attrs: {
          x: -75,
          y: -25,
          width: 150,
          height: 50,
          radius: 10,
          stroke: '#5B8FF9',
          fill: '#C6E5FF',
          lineWidth: 3,
        },
        name: 'rect-shape',
      });
      if (cfg.name) {
        group.addShape('text', {
          attrs: {
            text: cfg.name,
            x: 0,
            y: 0,
            fill: '#00287E',
            fontSize: 14,
            textAlign: 'center',
            textBaseline: 'middle',
            fontWeight: 'bold',
          },
          name: 'text-shape',
        });
      }
      return rect;
    },
  },
  'single-node',
);

const container = document.getElementById('container');
const width = container.scrollWidth;
const height = container.scrollHeight || 500;
const graph = new G6.Graph({
  container: 'container',
  width,
  height,
  layout: {
    type: 'dagre',
    ranksep: 70,
    controlPoints: true, 
  },
  defaultNode: {
    type: 'sql',
    size: [48, 48],
     anchorPoints: [
          // [0, 0]，代表节点左上角的锚点，[1, 1],代表节点右下角的锚点。
          [0.5, 0], // 顶部中心锚点
          [0.5, 1], // 底部中心锚点
        ],
  },
  defaultEdge: {
    type: 'cubic-vertical',
    sourceAnchor: 1,
    style: {
      // radius: 20,
      // offset: 45,
      // endArrow: true,
      lineWidth: 1,
      stroke: '#C9CDD4',
      shadowBlur: 10,
    },
  },
  nodeStateStyles: {
    selected: {
      stroke: '#d9d9d9',
      fill: '#5394ef',
    },
  },
  modes: {
    default: [
      'drag-canvas',
      'zoom-canvas',
      'click-select',

    ],
  },
  fitView: true,
});
graph.data(data);
graph.render();
graph.on('afterrender',()=>{
  const targerNode = graph.findById('3');
  const realModel = targerNode.getModel();
  graph.addItem("node", {
      id: 'shadowNode',
      x: realModel.x,
      y: realModel.y,
      label: '影子节点',
      anchorPoints: [[0, 0.5], [1, 0.5]],
    });
  graph.findById('shadowNode').hide();
  graph.addItem("node", {
      id: 'add1',
      x: realModel.x + 200 + 20 * 3,
      y: realModel.y,
      label: '额外节点',
      anchorPoints: [[0.5, 0], [0.5, 0]]
    });
     graph.addItem("edge", {
      source: 'shadowNode',
      target: 'add1',
      type: 'arc',
    });
     graph.addItem("node", {
      id: 'add11',
      x: realModel.x + 400 + 20 * 3,
      y: realModel.y,
      label: '额外节点2',
      anchorPoints: [[0.5, 0], [0.5, 0]]
    });
    graph.addItem("edge", {
      source: 'shadowNode',
      target: 'add11',
      type: 'arc',
    });
})
if (typeof window !== 'undefined')
  window.onresize = () => {
    if (!graph || graph.get('destroyed')) return;
    if (!container || !container.scrollWidth || !container.scrollHeight) return;
    graph.changeSize(container.scrollWidth, container.scrollHeight);
  };