Populate the cloud firestore document containing an array of document references - firebase

Question

I have a collection named campgrounds in which every document contains an array of document reference to the documents in the comments collections.
It looks like this Campground
I'm trying to figure out a way to populate this comments array before sending it to my ejs template.
My code looks like this
app.get("/campgrounds/:docId", function(req, res) {
var docRef = firestore.collection("campgrounds").doc(req.params.docId);
try {
docRef.get().then(doc => {
if (!doc.exists) {
res.send("no such document");
} else {
// res.send(doc.data());
res.render("campground", {
doc: doc.data(),
title: doc.data().title,
id: req.params.docId
});
}
});
} catch (error) {
res.send(error);
}
});

Answer 1

In your array you store DocumentReferences. If you want to get the data of the corresponding documents in order to include this data in your object you should use Promise.all() to execute the variable number (1 or more) of get() asynchronous operations.
The following should work (not tested at all however):
app.get("/campgrounds/:docId", function(req, res) {
var docRef = firestore.collection("campgrounds").doc(req.params.docId);
try {
var campground = {};
docRef.get()
.then(doc => {
if (!doc.exists) {
res.send("no such document");
} else {
campground = {
doc: doc.data(),
title: doc.data().title,
id: req.params.docId
};
var promises = [];
doc.data().comments.forEach((element, index) => {
promises.push(firestore.doc(element).get());
});
return Promise.all(promises);
}
})
.then(results => {
var comments = {};
results.forEach((element, index) => {
comments[index] = element.data().title //Let's imagine a comment has a title property
});
campground.comments = comments;
res.render("campground", campground);
})
} catch (error) {
res.send(error);
}
});
Note that with this code you are doing 1 + N queries (N being the length of the comments array). You could denormalize your data and directly store in the campground doc the data of the comments: you would then need only one query.