Firebase云函数TypeScript中为Snapshot指定数据类型的问题

你遇到的问题是firebase-functions/v1/firestore导出的QueryDocumentSnapshot并非泛型类型，所以无法直接通过<PaymentDocumentInterface>指定数据类型。以下几种方法可以解决这个问题，且无需声明额外变量做类型转换：

方法1：切换到Firebase Admin SDK的泛型类型 #

firebase-admin/firestore提供了支持泛型的QueryDocumentSnapshot，只需修改导入源即可：

import { firestore } from "firebase-functions/v1"
import { QueryDocumentSnapshot } from "firebase-admin/firestore";

interface PaymentDocumentInterface {
    amount: number;
    benefactorDetails: {
        email: string;
        marketingConsent: boolean;
    };
}

exports.updateDonationProjectAggregations = firestore.document('protectedEnvironmentData/financialData/payments/{paymentId}').onCreate(async (snapshot: QueryDocumentSnapshot<PaymentDocumentInterface>, context) => {
    console.log(`Processing payment with value: ${snapshot.data().amount}`);
});

方法2：直接在data()调用时添加类型断言 #

无需修改导入，直接对data()的返回值做类型断言，这是最轻量化的写法：

import { firestore } from "firebase-functions/v1"
import { QueryDocumentSnapshot } from "firebase-functions/v1/firestore";

interface PaymentDocumentInterface {
    amount: number;
    benefactorDetails: {
        email: string;
        marketingConsent: boolean;
    };
}

exports.updateDonationProjectAggregations = firestore.document('protectedEnvironmentData/financialData/payments/{paymentId}').onCreate(async (snapshot, context) => {
    console.log(`Processing payment with value: ${(snapshot.data() as PaymentDocumentInterface).amount}`);
});

方法3：自定义泛型类型扩展原有Snapshot #

如果希望保持原有导入源，同时保留泛型声明的写法，可以自己定义一个泛型类型来扩展原有的QueryDocumentSnapshot：

import { firestore } from "firebase-functions/v1"
import { QueryDocumentSnapshot as FunctionsSnapshot } from "firebase-functions/v1/firestore";

interface PaymentDocumentInterface {
    amount: number;
    benefactorDetails: {
        email: string;
        marketingConsent: boolean;
    };
}

// 自定义泛型类型，覆盖data()方法的返回类型
type QueryDocumentSnapshot<T> = FunctionsSnapshot & {
    data(): T;
};

exports.updateDonationProjectAggregations = firestore.document('protectedEnvironmentData/financialData/payments/{paymentId}').onCreate(async (snapshot: QueryDocumentSnapshot<PaymentDocumentInterface>, context) => {
    console.log(`Processing payment with value: ${snapshot.data().amount}`);
});

内容的提问来源于stack exchange，提问作者Sam