MongoDB: Query model and check if document contains object or not, then mark / group result - node.js

Question

I have a Model called Post, witch contains an property array with user-ids for users that have liked this post.
Now, i need to query the post model, and mark the returned results with likedBySelf true/false for use in by client - is this possible?
I dont have to store the likedBySelf property in the database, just modify the results to have that property.
A temporary solution i found was to do 2 queries, one that finds the posts that is liked by user x, and the ones that have not been liked by user x, and en map (setting likedBySelf true/false) and combine the 2 arrays and return the combined array. But this gives some limitations to other query functions such as limit and skip.
So now my queries looks like this:
var notLikedByQuery = Post.find({likedBy: {$ne: req.body.user._id}})
var likedByQuery = Post.find({likedBy: req.body.user._id})
(I'm using the Mongoose lib)
PS. A typical post can look like this (JSON):
{
"_id": {
"$oid": "55fc463c83b2d2501f563544"
},
"__t": "Post",
"groupId": {
"$oid": "55fc463c83b2d2501f563545"
},
"inactiveAfter": {
"$date": "2015-09-25T17:13:32.426Z"
},
"imageUrl": "https://hootappprodstorage.blob.core.windows.net/devphotos/55fc463b83b2d2501f563543.jpeg",
"createdBy": {
"$oid": "55c49e2d40b3b5b80cbe9a03"
},
"inactive": false,
"recentComments": [],
"likes": 8,
"likedBy": [
{
"$oid": "558b2ce70553f7e807f636c7"
},
{
"$oid": "559e8573ed7c830c0a677c36"
},
{
"$oid": "559e85bced7c830c0a677c43"
},
{
"$oid": "559e854bed7c830c0a677c32"
},
{
"$oid": "559e85abed7c830c0a677c40"
},
{
"$oid": "55911104be2f86e81d0fb573"
},
{
"$oid": "559e858fed7c830c0a677c3b"
},
{
"$oid": "559e8586ed7c830c0a677c3a"
}
],
"location": {
"type": "Point",
"coordinates": [
10.01941398718396,
60.96738099591897
]
},
"updatedAt": {
"$date": "2015-09-22T08:45:41.480Z"
},
"createdAt": {
"$date": "2015-09-18T17:13:32.426Z"
},
"__v": 8
}

Answer 1

#tskippe you can use a method like following to process whether the post is liked by the user himself and call the function anywhere you want.
var processIsLiked = function(postId, userId, doc, next){
var q = Post.find({post_id: postId});
q.lean().exec(function(err,res){
if(err) return utils.handleErr(err, res);
else {
if(_.find(doc.post.likedBy,userId)){ //if LikedBy array contains the user
doc.post.isLiked = true;
} else {
doc.post.isLiked = false;
}
});
next(doc);
}
});
}
Because you are using q.lean() you dont need to actually persist the data. You need to just process it , add isLiked field in the post and send back the response. **note that we are manuplating doc directly. Also you chan tweek it to accept doc containing array of posts and iterating it and attach an isLiked field to each post.

Answer 2

I found that MongoDB's aggregation with $project tequnique was my best bet. So i wrote up an aggregation like this.
Explanation:
Since i want to keep the entire document, but $project purpose is to modify the docs, thus you have to specify the properties you want to keep. A simple way of keeping all the properties is to use "$$ROOT".
So i define a $project, set all my original properties to doc: "$$ROOT", then create a new property "likedBySelf", which is marked true / false if a specified USERID is in the $likedBy set.
I think that this is more clean and simple, than querying every single model after a query to set a likedBySelf flag. It may not be faster, but its cleaner.
Model.aggregate([
{ $project: {
doc: "$$ROOT",
likedBySelf: {
$cond: {
"if": { "$setIsSubset": [
[USERID],
"$likedBy"
]},
"then": true,
"else": false
}
}
}}
]);