javascript - 重选和递归选择器

Question

我有一个带有项目树（标准化）的 redux 状态，例如：

state = {
  items: [
    { id: 1, parent: null, children: [2, 3] },
    { id: 2, parent: 1, children: [4] },
    { id: 3, parent: 1, children: [], value: 10 },
    { id: 4, parent: 2, children: [], value: 20 }
  ]
}

我想获得项目 1 的值的减少总和（这里 = 10 + 20 = 30），我想为此创建一个重新选择选择器。

但是，如何定义递归选择器？

谢谢你的帮助。;-)

弗雷德里克

Answer 1

我将更新@Vanojx1 代码以提出 2 个解决方案：

• 仅重新选择
• with reselect + re-reselect（在提供id更改时保持记忆）

（免责声明：我是重新选择的作者，但这是一个典型的用例）

基本代码

let state = {
    items: [
        { id: 1, parent: null, children: [2, 3] },
        { id: 2, parent: 1, children: [4] },
        { id: 3, parent: 1, children: [], value: 10 },
        { id: 4, parent: 2, children: [], value: 20 }
    ]
};

function getSum(items, id) {
  let item = items.find(item => item.id == id);
  return item.hasOwnProperty('value') ? item.value : item.children.reduce((current, next) => {
    return current + getSum(items, next);
  }, 0);
}

解决方案 1 - 仅重新选择

import { createSelector } from 'reselect';

const getSumSelector = createSelector(
  (state) => state.items,
  (state, id) => id,
  (items, id) => getSum(items, id)
);

getSumSelector(state, 1);
// Loses memoization with sequentials calls with same items but different id's

解决方案 2 - 重新选择 + 重新选择

import createCachedSelector from 're-reselect';

const getSumSelector = createCachedSelector(
    state => state.items,
    (state, id) => id,
    (items, id) => getSum(items, id)
)(
    // Cache selector by id
    (state, id) => id
);

getSumSelector(state, 1);

Answer 2

尝试这个：

let state = {
    items: [
        { id: 1, parent: null, children: [2, 3] },
        { id: 2, parent: 1, children: [4] },
        { id: 3, parent: 1, children: [], value: 10 },
        { id: 4, parent: 2, children: [], value: 20 }
    ]
}

function getSum(state, id) {
  let item = state.items.find(item => item.id == id);
  return item.hasOwnProperty('value') ? item.value : item.children.reduce((current, next) => {
    return current + getSum(state, next);
  }, 0);
}

let sum = getSum(state, 1);

console.log(sum);