我想向特定設(shè)備發(fā)送通知，所以我編寫了此函數(shù)及其工作正常，但我在用戶名中未定義日志輸出：得到這個(gè)after: { '-LhjfwZeu0Ryr6jYRq5r': { Price: '888', date: '2019-6-19', description: 'Ghh', id: 50, nameOfProblem: 'Vbh', providerName: 'Loy', providerService: 'Carpenter', statusInfo: 'Incomplete', time: '15:22', username:"devas" }}而且username是undefined這是函數(shù)exports.sendPushR = functions.database.ref('/request/{pid}/{uid}/orders')    .onWrite(async (snapshot, context) => {        const registrationTokens = "------";        const providerId = context.params.pid;        const userId = context.params.uid;        const event = context.params;        console.log("event", event);        console.log(`New Order from ${userId} to ${providerId}`);        const afterData = snapshot.after.val(); // data after the write        const username = snapshot.after.val().username;        console.log(afterData);        console.log(username);        const payload = {            notification: {                title: 'Message received',                body: `You received a new order from ${username} check it now! `,                sound: "default",                icon: "default",            }        };        try {            const response = await admin.messaging().sendToDevice(registrationTokens, payload);            console.log('Successfully sent message:', response);        }        catch (error) {            console.log('Error sending message:', error);        }        return null;    });