How to only get one value of child firebase cloud function? - node.js

Question

I want to send notifications that trigger into pengumuman topic.
export const onNotifPengumuman = functions.database.ref('/pengumuman_course/{course_id_p}/{pengumuman_id}')
.onCreate((snapshot,context) =>{
const course_id_p = context.params.course_id_p;
const pengumuman_id = context.params.pengumuman_id;
const nama_matkul = admin.database().ref('/courses/'+course_id_p+'name').once('value').then(snap =>{
return snapshot.val();
}).catch(error =>
{
console.log(error);
})
console.log(`cobacobacoba ${nama_matkul}`);
return admin.database().ref('pengumuman/' + pengumuman_id + '/').once('value').then(snap =>{
const pengumumanData = snap.val();
const notifDataPengumuman = {
data:{
data_type: "pengumuman ",
title: "Pengumuman Baru", // data bebas (key, value)
body: `${nama_matkul}`, // chatId = const chatId
sound: "default"
}
}
return admin.messaging().sendToTopic(course_id_p, notifDataPengumuman)
.then(function(response) {
console.log("Successfully sent message:", response);
})
.catch(function(error) {
console.log("Error sending message:", error);
});
}).catch(error => {
console.log(error);
})
});
In the first ref functions.database.ref('/pengumuman_course/{course_id_p}/{pengumuman_id}') I want to access and trigger this child in firebase real time database, the code below :
enter image description here
after that in this code return admin.database().ref('pengumuman/' + pengumuman_id + '/') I'm tring to get all of information about pengumuman and send it into users. The code in below :
enter image description here
But before that I want to get pengumuman name in the courses ref in the database to get value of name ,with this code :
const nama_matkul = admin.database().ref('/courses/'+course_id_p+'name').once('value').then(snap =>{
return snapshot.val();
}).catch(error =>
{
console.log(error);
})
enter image description here
The problem is when I'm using that code to get child name and store it into matkul, when I send/log ,it will return promises object. I want the result showing "REKAYASA PERANGKAT LUNAK".
Thanks and sorry for bad explanation
[FIXED]
Im trying the solution and found this code
export const onNotifPengumuman = functions.database.ref('/pengumuman_course/{course_id_p}/{pengumuman_id}')
.onCreate((snapshot,context) =>{
const course_id_p = context.params.course_id_p;
console.log(`course id pengumuman ${course_id_p}`);
const pengumuman_id = context.params.pengumuman_id;
admin.database().ref('/courses/' + course_id_p + '/').once('value').then(snap2 =>{
const nama_matkul = snap2.child('name').val();
console.log(`nama matkul dari sini ${nama_matkul}`);
admin.database().ref('pengumuman/' + pengumuman_id + '/').once('value').then(snap =>{
const pengumumanData = snap.val();
const notifDataPengumuman = {
data:{
data_type: "pengumuman",
title: "Pengumuman Baru", // data bebas (key, value)
body: `Judul :${nama_matkul}`, // chatId = const chatId
sound: "default"
}
}
return admin.messaging().sendToTopic(course_id_p, notifDataPengumuman)
.then(function(response) {
console.log("Successfully sent message:", response);
})
.catch(function(error) {
console.log("Error sending message:", error);
});
}).catch(error => {
console.log(error);
})
}).catch(error =>{
console.log(error);
})
});

Answer 1

You will need to resolve promises in order to get the value returned by them. What you are doing at the moment is assigning nama_matkul the promise but you never wait for it to complete.
Async/Await
You can either use async/await by defining your function as asynchronous:
.onCreate(async (snapshot,context) =>{
// Your asynchronous code here
}
You can then resolve the promise by running
const nama_matkul = (await admin.database().ref('/courses/'+course_id_p+'name').once('value')).val();
If you need to handle exceptions, wrap the promise and await in a try catch block.
After refactoring your code, it might look something like this:
export const onNotifPengumuman = functions.database.ref('/pengumuman_course/{course_id_p}/{pengumuman_id}')
.onCreate(async (snapshot,context) => {
try {
const course_id_p = context.params.course_id_p;
const pengumuman_id = context.params.pengumuman_id;
const nama_matkul = (await admin.database().ref('/courses/'+course_id_p+'name').once('value')).val();
console.log(`cobacobacoba ${nama_matkul}`);
const pengumumanData = (await admin.database().ref('pengumuman/' + pengumuman_id + '/').once('value')).val();
const notifDataPengumuman = {
data: {
data_type: "pengumuman ",
title: "Pengumuman Baru", // data bebas (key, value)
body: `${nama_matkul}`, // chatId = const chatId
sound: "default"
}
}
try {
await admin.messaging().sendToTopic(course_id_p, notifDataPengumuman);
console.log("Successfully sent message:", response);
} catch (messageSendError) {
console.log("Error sending message:", messageSendError);
}
} catch (error) {
console.log(error);
}
});
Then/Catch
If you do want to stick with the current setup you have and work with callbacks, you can instead keep the .then call and handle your application logic in the callback; your code might look something like this:
export const onNotifPengumuman = functions.database.ref('/pengumuman_course/{course_id_p}/{pengumuman_id}')
.onCreate((snapshot,context) => {
const course_id_p = context.params.course_id_p;
const pengumuman_id = context.params.pengumuman_id;
admin.database().ref('/courses/'+course_id_p+'name').once('value')
.then(nameSnapshot => {
const nama_matkul = nameSnapshot.val();
console.log(`cobacobacoba ${nama_matkul}`);
admin.database().ref('pengumuman/' + pengumuman_id + '/').once('value')
.then(dataSnapshot => {
const pengumumanData = dataSnapshot.val();
const notifDataPengumuman = {
data: {
data_type: "pengumuman ",
title: "Pengumuman Baru", // data bebas (key, value)
body: `${nama_matkul}`, // chatId = const chatId
sound: "default"
}
}
return admin.messaging().sendToTopic(course_id_p, notifDataPengumuman)
.then(response => console.log("Successfully sent message:", response))
.catch(error => console.log("Error sending message:", error));
})
.catch(error => console.log(error));
})
.catch(error => console.log(error))
});
You can of course use a combination of then/catch and await if you so wish, whether this is a good practice or when to use which really depends on the situation in which you use it.