normalizr - 为什么标准化状态形状中需要一个全为 `ids` 的数组？

Question

comments : {
    byId : {
        "comment1" : {
            id : "comment1",
            author : "user2",
            comment : ".....",
        },
        "comment2" : {
            id : "comment2",
            author : "user3",
            comment : ".....",
        },
        "comment3" : {
            id : "comment3",
            author : "user3",
            comment : ".....",
        },
        "comment4" : {
            id : "comment4",
            author : "user1",
            comment : ".....",
        },
        "comment5" : {
            id : "comment5",
            author : "user3",
            comment : ".....",
        },
    },
    allIds : ["comment1", "comment2", "comment3", "commment4", "comment5"]
}

在上面的示例中，我是否需要包含它 api 包含它。我认为这样你可以更快地进行计数，你可能可以排序，但通常我不明白是否会影响性能。

Answer 1

这不是 Redux 所要求的，这是一个标准化的东西。为了回答你的问题，JavaScript对象can't be replied upon to retain sort order in certain situations 。将 id 放入数组中可以让您保留规范化之前存在的排序顺序。

Quote from co-maintainer of Redux and author of "normalizing state shape section" of Redux docs :

As for the ID arrays, while JS engines now have a fairly standardized process for iterating across keys in an object, you shouldn't rely on that to define ordering. Storing arrays of IDs allows you to define an order for items.