Querying nested documents using Mongoose (MongoDB)

Question

I am starting out with mongodb and having hard time trying to query nested documents. I have two schemas:

var LinkSchema = new mongoose.Schema({
    url: String,
    name: String
});

var UserSchema = new mongoose.Schema({
    name: String,
    links: [LinkSchema]
});

As you can see, I am just tying to build a simple bookmarking tool. Each user has a name and a collection of links. Each link has a name and a url.

Now, what I am trying to do is for example, see if a link already exists in someone's links array. I would like to be able to do something like this (Trying to get vlad's link collection and then see if the query link already belongs to the collection or not):

app.get("/:query", function(req, res){
  User.findOne({"name":"vlad"}, function(err, user){
    user.links.find({"url":req.params.query}, function(err, foundLinks){
      if(foundLinks){
        res.send("link already exists!");
      } else {
        res.send("link doesn't exist!");
      }
    });
  });
});

Of course, this code doesn't work, because apparently I can't do a "user.links.find()". I guess I can just do a user.links.map to extract only urls and then run a membership query against it. But I think this would be far from the right solution. There's gotta be a way to do something like this natively using DB queries. Can someone help? Thank you!

steampowered · Accepted Answer · 2015-07-30 21:27:54Z

79

You can query an embedded document in mongoose like this

   User.find({'links.url':req.params.query}, function(err, foundUsers){
      // ---
   });

and to find the links that belong to the user "vlad", you can write

   User.find({name:'vlad','links.url':req.params.query}, function(err, foundUsers){
      // ---
   });

This will do the trick.

edited Jul 30, 2015 at 21:27

steampowered

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answered Oct 27, 2012 at 14:01

RameshVel

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8 Comments

geevee Over a year ago

why the returned parameter is foundLinks and not foundUsers ?

Rémi Becheras Over a year ago

Could you answer to @geevee comment ?

RameshVel Over a year ago

@RémiBecheras @geevee It should be foundUsers, but i just used the code the OP had originally posted.. it was foundLinks there.. you can check that :)

Rémi Becheras Over a year ago

Thank you. We asked because if it was right, we missed something big.... I just edited your post to fixing it

jmcollin92 Over a year ago

Thanks for this answer but those queries returns Users and not only Link as asked by @vlad. Is there a way to retreive only Links ?

|

Sritam · Accepted Answer · 2018-10-06 17:17:00Z

3

To find a specific link that belongs to a specific user you can do this

User.find({name:'vlad','links.url':req.params.query}, { 'links.$': 1 },  function(err, foundUsers){
      // ---
   });

answered Oct 6, 2018 at 17:17

Sritam

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2 Comments

ram Over a year ago

What is the { 'links.$' : 1 } part called? I'm looking for the documentation on this feature. I'm assuming it's saying to just return the one nested document?

ViaxCo Over a year ago

Adding to this, const foundLinks = foundUsers.links[0]

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