TypeScript：不允许多个构造函数实现

Question

我有一个对象，我在多个服务中使用它，每个服务都应该接受一些参数，所以我创建了两个构造函数，但 TypeScript 不允许我这样做，我的例子是：

class User {
   id: number;
   username: string;
   password: string;
   email: string;
   firstName: string;
   lastName: string;
   roles: string[];

   constructor(username: string, password: string){
       this.username = username;
       this.password = password;
   }

   constructor(id: number, username: string, firstname: string, lastname: string, roles: string[]){
       this.id = id;
       this.username= username;
       this.firstname= firstname;
       this.lastname= lastname;
       this.roles = roles;
   }
   //.. and maybe another constructor also
}

请问有什么技巧可以解决这个问题吗？

---

例如，当我?在构造函数中使用 Optional时：

constructor(
    public id?: number,
    public username?: string,
    public email?: string,
    public password?: string,
    public firstName?: string,
    public lastName?: string,
    public roles?: string[]) {
}

当我从后端获取数据时：

this.service.usersList().subscribe(users => {
  console.log(users);
  this.dataSource.data = users;
});

将roles在设置的密码，而不是在角色失败：

{
  "id": 1,
  "username": "user1",
  "email": "user1@email.com",
  "password": [
    "USER",
    "MODR"
  ]
}

为此，我不确定这个技巧。

---

也许我不精确，但我使用这种方法来解析我的数据：

static fromJson(item: Object): any {
    return new User(
        item['id'],
        item['username'],
        item['email'],
        item['roles']
    );
}

为此，当我创建一个可选的构造函数时，它将按照我的调用顺序设置属性。

Answer 1

你不能使用多个构造函数，但你可以添加一些可选参数，并验证它是否存在，就像这样：

class User {
    id: number;
    username: string;
    password: string;
    email: string;
    firstName: string;
    lastName: string;
    roles: string[];
    // The "?" says that its optional parameter
    constructor(id?: number, username?: string, firstname?: string,
        lastname?: string, roles?: string[], password?: string) {
        if (id) { // if id exists , you can implement the first constructor
            this.id = id;
            this.username = username;
            this.firstname = firstname;
            this.lastname = lastname;
            this.roles = roles;
        }
        if (password) { // if password exists : you can implement the second one
            this.username = username;
            this.password = password;
        }
    }
}

在此正常工作之前，您的回复应该是这样的：

static fromJson(item: Object): any {
    return new User({
        id : item['id'],
        username : item['username'],
        email : item['email'],
        roles : item['roles']
    });
}

所以你的构造函数应该是这样的：

constructor(user: any){
    if (user.id) { // if id exists , you can implement the first constructor
        this.id = user.id;
        this.username = user.username;
        this.firstname = user.firstname;
        this.lastname = user.lastname;
        this.roles = user.roles;
    }
    if (user.password) { // if password exists : you can implement the second one
        this.username = user.username;
        this.password = user.password;
    }
}

或者，如果您不想这样做，您可以设置有关订单的响应，如下所示：

static fromJson(item: Object): any {
    return new User(
        item['id'],
        item['username'],
        undefined,
        item['email'],
        undefined,
        undefined,
        item['roles']
    );
}