Retrieving data from MongoDB ánd MySQL simultaneously - mysql

Question

I am trying to retrieve data from my MongoDB database which stores chat conversations. This works fine and returns what I want. However, I only save userIDs in MongoDB, so I need to query profile picture, username etc from my MySQL database. I tried the following:
app.get('/api/retrieveAllChats', (req, res) => {
var Conversation = mongoose.model('Conversation', ConversationSchema);
var ChatMessage = mongoose.model('Message', ChatMessageSchema);
var userID = req.query.userID.toString()
var members = []
var conversationData = []
var retrieveAllChats = new Promise(function(resolve, reject) {
Conversation.aggregate([{ $match: { "members.uID": userID } }, { $lookup: { foreignField: "c_ID", from: "messages", localField: "_id", as: "messages" } }, { "$unwind": "$messages" }, { "$sort": { "messages.t": -1 } }, { "$group": { "_id": "$_id", "lastMessage": { "$first": "$messages" }, "allFields": { "$first": "$$ROOT" } } }, { "$replaceRoot": { "newRoot": { "$mergeObjects": [ "$allFields", { "lastMessage": "$lastMessage" } ] } } }, { "$project": { "messages": 0 } }], function (err, conversations) {
if (err) return handleError(err);
conversations.forEach((conversation, i) => {
return new Promise(function (resolveConversations, rejectConversations) {
var membersPromise = conversation.members.forEach((member, x) => {
return new Promise(function (resolveUserData, rejectUserData) {
getUserData(member["uID"], function(userData) {
members.push({userID: member["uID"], joinDate: member["j"], userName: userData["userName"], userDisplayName: userData["userDisplayName"], userVerified: userData["userVerified"], userProfilePicURL: userData["userProfilePicURL"]})
console.log("userData: ", userData)
conversations[i].members[x].userData = userData
conversationData = conversations
resolveUserData({userID: member["uID"], joinDate: member["j"], userName: userData["userName"], userDisplayName: userData["userDisplayName"], userVerified: userData["userVerified"], userProfilePicURL: userData["userProfilePicURL"]})
})
})
})
resolveConversations()
})
})
resolve()
})
}).catch(error => {
console.log(error)
res.json({ errorCode: 500 })
})
retrieveAllChats.then(function() {
res.header("Content-Type",'application/json');
res.send(JSON.stringify(conversationData, null, 4));
})
})
However, the conversationData array is always empty. So I need a way to resolve the retrieveAllChats promise and pass the data I added to the existing conversations object to return it with all information I need. Any ideas on how I can do this? (getUserData is a function to retrieve the MySQL data, this one works fine and returns what I want)

Answer 1

You are trying to do async operation inside forEach which wouldn't work. You need to either use for...of or Promise.all.
Also, you can make this code much cimpler by using .exec() at the end of running any query or aggregation as that is supported by mongoose. Something like this should work. Make sure you change your routte line to this to tell it is an async function
app.get("/api/retrieveAllChats", async (req, res) => {
core logic
const conversions = await Conversation.aggregate([{"$match": {"members.uID": userID}}, {"$lookup": {"foreignField": "c_ID", "from": "messages", "localField": "_id", "as": "messages"}}, {"$unwind": "$messages"}, {"$sort": {"messages.t": -1}}, {"$group": {"_id": "$_id", "lastMessage": {"$first": "$messages"}, "allFields": {"$first": "$$ROOT"}}}, {"$replaceRoot": {"newRoot": {"$mergeObjects": ["$allFields", {"lastMessage": "$lastMessage"}]}}}, {"$project": {"messages": 0}}]);
for(const conversation of conversations) {
for(const member of conversation.members) {
// add your promise call here and either await it or use then to get the promise value.
}
}