typescript 装饰器 + 反射(reflect)元数据

Question

我正在使用属性装饰器 Field将它的键推到 fields反射(reflect)元数据属性:

export function Field(): PropertyDecorator {
    return (target, key) => {
        const fields = Reflect.getMetadata('fields', target) || [];
        if (!fields.includes(key)) {
            fields.push(key)
        }
        Reflect.defineMetadata('fields', fields, target)
    }
}

然后我有一个抽象基类 Form访问 getter 附件中的元数据:

abstract class Form {
    get fields() {
        return Reflect.getMetadata('fields', this) || [];
    }
}

到目前为止，我已经能够成功地使用它来区分表单字段和其他类属性。考虑这些类:

abstract class UserForm extends Form {
    @Field()
    public firstName: string

    @Field()
    public lastName: string

    get fullName() {
        return this.firstName + ' ' + this.lastName;
    }
}

class AdminForm extends UserForm {
    @Field()
    roles: string[]
}

const form = new AdminForm()
console.log(form.fields)
// ['roles', 'firstName', 'lastName']

当我将姐妹类定义为 AdminForm 时会出现问题- MemberForm .当多个子类存在到 Form似乎 fields getter 返回所有字段:

class MemberForm extends UserForm {
    @Field()
    memberSince: Date;
}

const form = new AdminForm()
console.log(form.fields)
// ['roles', 'firstName', 'lastName', 'memberSince'] <--!!!

这对我来说毫无意义。为什么 memberSince字段出现在 AdminForm 的实例上?如何在不同的子类上定义不同的字段？

Answer 1

问题是getMetadata沿着原型(prototype)链向下，并且总是返回在基本类型上定义的内容(因为首先分配)。您需要使用 getOwnMetadata仅在添加新字段时获取当前类的数组字段，并且在获取字段时，您需要向上走属性链以获取所有基类字段。

这应该有效:

import 'reflect-metadata'
export function Field(): PropertyDecorator {
  return (target, key) => {
      const fields = Reflect.getOwnMetadata('fields', target) || [];
      if (!fields.includes(key)) {
          fields.push(key)
      }
      Reflect.defineMetadata('fields', fields, target)
  }
}

abstract class Form {
  get fields() {
      let fields = []
      let target = Object.getPrototypeOf(this);
      while(target != Object.prototype) {
        let childFields = Reflect.getOwnMetadata('fields', target) || [];
        fields.push(...childFields);
        target = Object.getPrototypeOf(target);
      }
      return fields;
  }
}

abstract class UserForm extends Form {
  @Field()
  public firstName!: string

  @Field()
  public lastName!: string

  get fullName() {
      return this.firstName + ' ' + this.lastName;
  }
}

class AdminForm extends UserForm {
  @Field()
  roles!: string[]
}

const form1 = new AdminForm()
console.log(form1.fields) // ['roles', 'firstName', 'lastName']

class MemberForm extends UserForm {
  @Field()
  memberSince!: Date;
}

const form2 = new MemberForm()
console.log(form2.fields) // ["memberSince", "firstName", "lastName"]