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I am attempting to implement push notifications for a group chat app whose database structure is pasted below. I was wondering how to use the conversation_users node to only send push notifications if the user's a part of that conversation and also how to send push notifications to multiple devices since the code I have right now only sends it to my device using its specific fcmToken. Should I be subscribing users to topics, with those topics being the separate conversationIds? This is my first time using FCM, so any guidance would be greatly appreciated.

Database Structure:

 conversation_messages 
 conversationId: 
 message1: 
 text: "Hello"
 timestamp: 1095819823.123
 senderId: aSLKN12KLSDNFK
 
 
 , 
 conversation_users 
 conversationId: 
 userUID:1
 userUID2:1
 
 ,
 users 
 userUID: 
 fcmToken: "fcmToken"
 bio: "bio"
 username: "username"
 
 

Index.js code: Right now this code sends push notifications onto my device for any messages sent within the app. I'm looking to limit notifications to only the conversations the user has joined and to prevent push notifications for messages that I sent.

exports.observeMessages = functions.database.ref('/conversation_messages/convoId/messageId')
 .onCreate((snapshot, context) => 

 var convoId = context.params.convoId;
 var messageId = context.params.messageId;
 var message = snapshot.val();

 return admin.database().ref('/conversations/' + convoId).once('value', snapshot => 

 var conversation = snapshot.val(); // This gives us the conversation name

 return admin.database().ref('/users/' + message.senderId).once('value', snapshot => 

 var user = snapshot.val();

 var notification = 
 notification: 
 title: conversation.conversationName,
 body: user.username + ": " + message.text
 ,
 token: 'dFlruzs91OM:APA91bHVx-Ga11GZ4fEwGAkrvFIegXPgPkvFrNuYa0U6yL_bdC7urM721SQGdnylpBNYPYMWAFpLbDk7pahe1RUMlQ8rN7iK7EAU89Xg6xpbIcBi6ZbTM7TB8N5zxPwhq0MTdIxIRH61'
 

 admin.messaging().send(notification)
 .then((response) => 
 // Response is a message ID string.
 console.log('Successfully sent message:', response);
 return response
 )
 .catch((error) => 
 console.log('Error sending message:', error);
 throw new Error("Error sending message");
 );

 )

 )

 )