如何根据对象属性值应用接口

Question

I wrote it again by summarizing the contents of the article.

我想知道如何根据对象属性值应用接口。

我在下面写了一个简单的示例代码。

一共有三个节点：root、dept、user。

指定每个节点对应的类型。因此，我们希望根据对象类型属性来指定接口。

但是，您可以看到您正在手动确认类型，因为您还没有找到解决方案。

为了解决这个问题，我认为应该用索引类型而不是条件类型来解决。

原因是条件类型期望根据泛型类型参数计算返回，但当前问题应该是根据现有类型计算而不是接收类型参数。

但是，即使使用两种方法也无法解决问题。任何帮助将不胜感激??????♂️

export enum NodeType {
  root = "root",
  dept = "dept",
  user = "user",
}

interface Node {
  readonly type: NodeType;
  title: string;
}

interface RootNode extends Node {
  type: NodeType.root;
}

interface DeptNode extends Node {
  type: NodeType.dept;
  departmentCode: string;
}

interface UserNode extends Node {
  type: NodeType.user;
  employeeNumber: string;
}

const nodeData: Node[] = [
  {
    type: NodeType.root,
    title: "Company 1",
  } as RootNode,
  {
    type: NodeType.dept,
    title: "Department 1",
    departmentCode: "557",
    // The type is not inferred according to the object property type, so the type must be explicitly asserted.
  } as DeptNode,
  {
    type: NodeType.user,
    title: "User 1",
    employeeNumber: "201911",
  } as UserNode,
];

// I want to be the type of DeptNode interface because the type of object property is NodeType.dept.
const selectDept = nodeData.filter((x) => x.type === NodeType.dept);
selectDept.forEach((x) => {
  console.log({
    type: x.type,
    title: x.title,
    // The type is not affirmed in the node that fits the object property type, so you have to affirm the type yourself.
    departmentCode: (x as DeptNode).departmentCode,
  });
});

Answer 1

我知道如何使用types，而不是interfaces。

您的尝试有两个问题：

1. 通过使用类型，您可以利用discriminated unions （注意 Node 类型是三种可能情况的并集）。
2. 对于filter和forEach等数组方法，推断 算法不够聪明，无法理解请求的内容 类型，因此您必须使用简单的for 和if。在这里阅读更多：https://stackoverflow.com/a/62033938/632445

我们开始吧：

export enum NodeType {
    root = "root",
    dept = "dept",
    user = "user",
}

type NodeBase = {
    readonly type: NodeType;
    title: string;
}

type RootNode = NodeBase & {
    type: NodeType.root;
}

type DeptNode = NodeBase & {
    type: NodeType.dept;
    departmentCode: string;
}

type UserNode = NodeBase & {
    type: NodeType.user;
    employeeNumber: string;
}

type Node = RootNode | DeptNode | UserNode;

const nodeData: Node[] = [
    {
        type: NodeType.root,
        title: "Company 1",
    },
    {
        type: NodeType.dept,
        title: "Department 1",
        departmentCode: "557",
        // The type is not inferred according to the object property type, so the type must be explicitly asserted.
    },
    {
        type: NodeType.user,
        title: "User 1",
        employeeNumber: "201911",
    },
];

// I want to be the type of DeptNode interface because the type of object property is NodeType.dept.
for (const x of nodeData) {
    if (x.type === NodeType.dept) {
        console.log({
            type: x.type,
            title: x.title,
            // The type is not affirmed in the node that fits the object property type, so you have to affirm the type yourself.
            departmentCode: (x as DeptNode).departmentCode,
        });
    }
}