如何使用类转换器将 typescript class 转换为普通 javascript object

Question

我的 angular 应用程序中有一些 typescript 类实例，我必须保存到 firebase。 Firebase 不支持自定义类，所以我发现这个： https://github.com/typestack/class-transformer似乎很适合我。

所以现在我正在创建我的 object，并尝试对其进行转换。

这是我的 object。

export class Trip {
  id: string;
  owner: string;
  name: string;
  @Type(() => Date)
  startDate: Date;
  @Type(() => Date)
  endDate: Date | undefined;
  coverImageUrl: string;

  @Type(() => Itinerary)
  itinerary: Itinerary;

  constructor() {
    this.itinerary = new Itinerary();
  }
}

export class Itinerary {
  @Type(() => ItineraryStats)
  stats: ItineraryStats;
  @Type(() => Step, {
    discriminator: {
      property: '__type',
      subTypes: [
        { value: ActivityStep, name: 'ActivityStep' },
        { value: NightStep, name: 'NightStep' },
        { value: PointOfInterest, name: 'PointOfInterest' },
        { value: TravelStep, name: 'TravelStep' },
      ],
    },
  })
  steps: Step[];

  constructor() {
    this.steps = Step[0];
    this.stats = new ItineraryStats();
  }
}

export class ItineraryStats {
  ///In days
  duration: number;
  //in hours
  driveTime: number;
  //in kilometers
  driveDistance: number;

  averageDriveDistancePerDay(): number {
    return this.driveDistance / this.duration;
  }
  averageDriveTimePerDay(): number {
    return this.driveTime / this.duration;
  }
}


export abstract class Step {
  @Type(() => Date)
  start: Date;

  @Type(() => Date)
  end: Date;
  duration: number;
  enforcedStartStop: boolean;
  warning: string;
}

export class ActivityStep extends StopStep {
  duration: number;

  constructor() {
    super();
    this.id = Guid.newGuid();
  }
}


export class NightStep extends StopStep {
  nightNumber: number;
  numberOfNight: number;
}

export class PointOfInterest {
  @Type(()=>PointOfInterest)
  type: PointOfInterest;
}


export class TravelStep extends Step {
  @Type(() => TravelMode)
  Mode: TravelMode;
  PolyLines: string;
}

我正在创建一个“旅行”并尝试对其进行转换：

const trip = new Trip();
trip.owner= firebase.auth().currentUser.uid;
trip.name= action.name;
trip.startDate = action.startDate,
trip.endDate = action.endDate;
console.log(trip);
const converted = classToPlain(trip)

但我明白了：

ERROR TypeError: Cannot read property 'constructor' of undefined
    at TransformOperationExecutor.js:207
    at Array.find (<anonymous>)
    at TransformOperationExecutor.transform (TransformOperationExecutor.js:207)
    at TransformOperationExecutor.transform (TransformOperationExecutor.js:266)
    at ClassTransformer.classToPlain (ClassTransformer.js:10)
    at classToPlain (index.js:8)
    at Object.toFirestore (trips.firestore.ts:16)
    at ma (index.cjs.js:15983)
    at n.set (index.cjs.js:15359)
    at AngularFirestoreDocument.set (angular-fire-firestore.js:512)

我刚刚创建的 object：

我猜我的 object 是不正确的 state 或者我的定义不明确，但我找不到什么？

Answer 1

错误在于Itinerary的定义，更具体地说是代码行this.steps = Step[0]; 它将变量设置为未定义，很可能不是故意的。 class-transformer器库可以处理属性steps是一个空数组、步骤数组或首先不存在但当值设置为未定义时崩溃。

export class Itinerary {
  @Type(() => ItineraryStats)
  stats: ItineraryStats;
  @Type(() => Step, {
    discriminator: {
      property: '__type',
      subTypes: [
        { value: ActivityStep, name: 'ActivityStep' },
        { value: NightStep, name: 'NightStep' },
        { value: PointOfInterest, name: 'PointOfInterest' },
        { value: TravelStep, name: 'TravelStep' },
      ],
    },
  })
  steps: Step[];

  constructor() {
    // Step[0] causes the crash, because its undefined, either dont set it or 
    // set it to this.steps = []
    this.steps = Step[0]; 
    this.stats = new ItineraryStats();
  }
}

更多细节：由于在属性steps上使用了鉴别器，相应的逻辑启动并将subTypes下定义的构造函数与当前值的构造函数进行比较以找到正确的子类型名称：

    if (this.transformationType === TransformationType.CLASS_TO_PLAIN) {
      subValue[targetType.options.discriminator.property] = targetType.options.discriminator.subTypes.find(
        subType => subType.value === subValue.constructor
      ).name;
    }

链接到 github

Step[0]未定义最终使这一行subValue.constructor崩溃。