Mongoose load, limit and skip data from two collections - node.js

Question

I am building a MERN stack social media application. On the application, a user can have a profile with posts which can either be a photo or a video.
My photos are stored in the posts collection, however, videos are stored in a collection named media.
When the user wants to view their posts, I have a function that gets all data from both collections, sorts them by their date of creation and returns them to the frontend. This has been working fine until the user builds up a large number of photos/videos, and now MongoDB won't allow that user to make the request anymore as it takes too much RAM.
I want to implement a lazy-load onto this so I'm not requesting all this data that the user doesn't even need, and I know how to do this using a single collection, however, I'm not sure how I would go about doing it when using two collections.
I know I would limit each collection to 2 objects at one time and add a skip to each to request the next two objects, but I don't know how to keep track of which needs to come next, a photo or a video?
My current code:
//First function, called by route
const listPostAndMediaByUser = (req, res) => {
sortMediaAndPosts(req)
.then(function(postsAndMedia) {
return res.json(postsAndMedia);
})
.catch(function(error) {
console.log("Error getting posts", error)
return res.status(400).json({
error: errorHandler.getErrorMessage(error)
});
});
};
//Sorting function
//This function runs getPosts, and getMedia
//And sorts them by their creation date
const sortMediaAndPosts = function(req) {
return new Promise(async function(resolve, reject) {
let postsAndMedia = [];
try {
const posts = await getPosts(req);
const media = await getMedia(req);
postsAndMedia = [...posts, ...media].sort(
(a, b) => new Date(b.created) - new Date(a.created)
);
} catch (error) {
console.log('Error: ', error);
reject(error);
}
resolve(postsAndMedia);
});
};
//Get posts function
const getPosts = function(req) {
return new Promise(async function(resolve, reject) {
try {
Post.find({ postedBy: req.profile._id })
.limit(2)
.select('-photo')
.populate('postedBy', '_id name')
.populate('comments.postedBy', '_id name')
.sort('-created')
.exec((err, posts) => {
if (err) reject(err);
else resolve(posts);
});
} catch(e) {
console.log('error!', e)
reject(e);
}
});
};
//Get Media function
const getMedia = function (req) {
return new Promise(async function(resolve, reject) {
Media.find({postedBy: req.profile._id})
.limit(2)
.populate('postedBy', '_id name')
.populate('comments.postedBy', '_id name')
.sort('-created')
.exec((err, media) => {
if(err) reject(err)
else resolve(media)
})
})
}
Any input would be greatly appreciated.
Thanks

Answer 1

Your schemas for Post and Media look very similar. You should consider merging them into a single schema. This would resolve your problem.
If you don't want to change your schema you should look into the mongodb aggregation pipeline which allows you to join data from multiple collections (using $lookup).