Clean up dead references with Mongoose populate()

Question

If a user has an array called "tags":

var User = new Schema({
    email: {
        type: String,
        unique: true,
        required: true
    },
    tags: [{
        type: mongoose.Schema.Types.ObjectId,
        ref:'Tag',
        required: true
    }],
    created: {
        type: Date,
        default: Date.now
    }
});

and I do a populate('tags') on a query:

User.findById(req.params.id)
    .populate("tags")
    .exec(function(err, user) { ... });

If one of the tags in the list has actually been deleted, is there a way to remove this dead reference in "tags"?

Currently, the returned user object IS returning the desired result -- ie. only tags that actually exist are in the tags array... however, if I look at the underlying document in mongodb, it still contains the dead tag id in the array.

Ideally, I would like to clean these references up lazily. Does anyone know of a good strategy to do this?

score 5 · Accepted Answer · answered May 24 '17 at 05:32

I've tried to find some built-in way to do that but seems that mongoose doesn't provide such functionality.

So I did something like this

User.findById(userId)
    .populate('tags')
    .exec((err, user) => {
        user.tags = user.tags.filter(tag => tag != null);

        res.send(user); // Return result as soon as you can
        user.save(); // Save user without dead refs to database
    })

This way every time you fetch user you also delete dead refs from the document. Also, you can create isUpdated boolean variable to not call user.save if there was no deleted refs.

const lengthBeforeFilter = user.tags.length;
let isUpdated = user.tags.length;

user.tags = user.tags.filter(tag => tag != null);
isUpdated = lengthBeforeFilter > user.tags.length;

res.send(user);

if (isUpdated) {
    user.save();
}

score 0 · Answer 2 · answered Dec 19 '16 at 05:58

0

Assuming you delete these tags via mongoose, you can use the post middleware.

This will be executed after you've deleted a tag.

tagSchema.post('remove', function(doc) {
     //find all users with referenced tag
     //remove doc._id from array
});

answered Dec 19 '16 at 05:58

Camo

1,122
10
15

It seems strange, but I was hoping to find a way to do it that doesn't require removing the tag from each user at the time of deletion.... rather, I'd like to do it on populate the next time the user is fetched. – Garett Dec 19 '16 at 06:36
I have a database with millions of tagged users... On it, I would like to have *temporary* dead references that get cleaned up over time instead of hitting hard whenever a tag is deleted from the system. – Garett Dec 19 '16 at 16:50

score -1 · Answer 3 · answered Oct 24 '22 at 22:32

-1

its sample retainNullValues: true

Example:

 User.findById(req.params.id)
 .populate({
      path: "tag",
      options: {
        retainNullValues: true
      }
    })

answered Oct 24 '22 at 22:32

Rahman Rezaee

1,943
16
24

Clean up dead references with Mongoose populate()

3 Answers3

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