将平面对象数组转换为嵌套对象

我有以下数组（实际上来自后端服务）：

const flat: Item[] = [
    { id: 'a', name: 'Root 1', parentId: null },
    { id: 'b', name: 'Root 2', parentId: null },
    { id: 'c', name: 'Root 3', parentId: null },

    { id: 'a1', name: 'Item 1', parentId: 'a' },
    { id: 'a2', name: 'Item 1', parentId: 'a' },

    { id: 'b1', name: 'Item 1', parentId: 'b' },
    { id: 'b2', name: 'Item 2', parentId: 'b' },
    { id: 'b2-1', name: 'Item 2-1', parentId: 'b2' },
    { id: 'b2-2', name: 'Item 2-2', parentId: 'b2' },
    { id: 'b3', name: 'Item 3', parentId: 'b' },

    { id: 'c1', name: 'Item 1', parentId: 'c' },
    { id: 'c2', name: 'Item 2', parentId: 'c' }
];

where Item is:

interface Item {
    id: string;
    name: string;
    parentId: string;
};

为了与显示树（类似文件夹）视图的组件兼容，需要将其转换为：

const treeData: NestedItem[] = [
    {
        id: 'a',
        name: 'Root 1',
        root: true,
        count: 2,
        children: [
          {
            id: 'a1',
            name: 'Item 1'
          },
          {
            id: 'a2',
            name: 'Item 2'
          }
        ]
    },
    {
        id: 'b',
        name: 'Root 2',
        root: true,
        count: 5, // number of all children (direct + children of children)
        children: [
          {
            id: 'b1',
            name: 'Item 1'
          },
          {
            id: 'b2',
            name: 'Item 2',
            count: 2,
            children: [
                { id: 'b2-1', name: 'Item 2-1' },
                { id: 'b2-2', name: 'Item 2-2' },
            ]
          },
          {
            id: 'b3',
            name: 'Item 3'
          },
        ]
    },
    {
        id: 'c',
        name: 'Root 3',
        root: true,
        count: 2,
        children: [
          {
            id: 'c1',
            name: 'Item 1'
          },
          {
            id: 'c2',
            name: 'Item 2'
          }
        ]
    }
];

where NestedItem is:

interface NestedItem {
    id: string;
    name: string;
    root?: boolean;
    count?: number;
    children?: NestedItem[];
}

到目前为止我所尝试过的都是这样的：

// Get roots first
const roots: NestedItem[] = flat
    .filter(item => !item.parentId)
    .map((item): NestedItem => {
        return { id: item.id, name: item.name, root: true }
    });

// Add "children" to those roots
const treeData = roots.map(node => {
    const children = flat
        .filter(item => item.parentId === node.id)
        .map(item => {
            return { id: item.id, name: item.name }
        });
    return {
        ...node,
        children,
        count: node.count ? node.count + children.length : children.length
    }
});

但这当然只能获得第一级子节点（根节点的直接子节点）。它以某种方式需要递归，但我不知道如何实现这一点。

不假设展平数组的顺序或嵌套对象的深度：

Array.prototype.reduce足够灵活来完成这项工作。如果您不熟悉Array.prototype.reduce我建议读这个 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce。您可以通过执行以下操作来实现此目的。

我这里有两个依赖递归的函数：findParent and checkLeftOvers. findParent尝试找到对象父对象并返回true or false根据是否找到它。在我的减速器中，我将当前值添加到剩余数组中，如果findParent回报false. If findParent回报true I call checkLeftOvers查看我的剩余数组中是否有任何对象是该对象的子对象findParent刚刚添加。

注：我添加了{ id: 'b2-2-1', name: 'Item 2-2-1', parentId: 'b2-2'} to the flat数组来证明这将按照您的意愿进行深入。我也重新订购了flat证明这在这种情况下也适用。希望这可以帮助。

const flat = [
    { id: 'a2', name: 'Item 1', parentId: 'a' },
    { id: 'b2-2-1', name: 'Item 2-2-1', parentId: 'b2-2'},
    { id: 'a1', name: 'Item 1', parentId: 'a' },
    { id: 'a', name: 'Root 1', parentId: null },
    { id: 'b', name: 'Root 2', parentId: null },
    { id: 'c', name: 'Root 3', parentId: null },
    { id: 'b1', name: 'Item 1', parentId: 'b' },
    { id: 'b2', name: 'Item 2', parentId: 'b' },
    { id: 'b2-1', name: 'Item 2-1', parentId: 'b2' },
    { id: 'b2-2', name: 'Item 2-2', parentId: 'b2' },
    { id: 'b3', name: 'Item 3', parentId: 'b' },
    { id: 'c1', name: 'Item 1', parentId: 'c' },
    { id: 'c2', name: 'Item 2', parentId: 'c' }
];

function checkLeftOvers(leftOvers, possibleParent){
  for (let i = 0; i < leftOvers.length; i++) {
    if(leftOvers[i].parentId === possibleParent.id) {
      delete leftOvers[i].parentId
      possibleParent.children ? possibleParent.children.push(leftOvers[i]) : possibleParent.children = [leftOvers[i]]
      possibleParent.count = possibleParent.children.length
      const addedObj = leftOvers.splice(i, 1)
      checkLeftOvers(leftOvers, addedObj[0])
    }
  }
}

function findParent(possibleParents, possibleChild) {
  let found = false
  for (let i = 0; i < possibleParents.length; i++) {
    if(possibleParents[i].id === possibleChild.parentId) {
      found = true
      delete possibleChild.parentId
      if(possibleParents[i].children) possibleParents[i].children.push(possibleChild)
      else possibleParents[i].children = [possibleChild]
      possibleParents[i].count = possibleParents[i].children.length
      return true
    } else if (possibleParents[i].children) found = findParent(possibleParents[i].children, possibleChild)
  } 
  return found;
}
 
 const nested = flat.reduce((initial, value, index, original) => {
   if (value.parentId === null) {
     if (initial.left.length) checkLeftOvers(initial.left, value)
     delete value.parentId
     value.root = true;
     initial.nested.push(value)
   }
   else {
      let parentFound = findParent(initial.nested, value)
      if (parentFound) checkLeftOvers(initial.left, value)
      else initial.left.push(value)
   }
   return index < original.length - 1 ? initial : initial.nested
 }, {nested: [], left: []})
 
console.log(nested)