Mongoose: Populate a populated field

问题

I'm using MongoDB as a log keeper for my app to then sync mobile clients. I have this models set up in NodeJS:

var UserArticle = new Schema({
    date: { type: Number, default: Math.round((new Date()).getTime() / 1000) }, //Timestamp!
    user: [{type: Schema.ObjectId, ref: "User"}],
    article: [{type: Schema.ObjectId, ref: "Article"}],
    place: Number,    
    read: Number,     
    starred: Number,   
    source: String
});
mongoose.model("UserArticle",UserArticle);

var Log = new Schema({
    user: [{type: Schema.ObjectId, ref: "User"}],
    action: Number, // O => Insert, 1 => Update, 2 => Delete
    uarticle: [{type: Schema.ObjectId, ref: "UserArticle"}],
    timestamp: { type: Number, default: Math.round((new Date()).getTime() / 1000) }
});
mongoose.model("Log",Log);

When I want to retrive the log I use the follwing code:


var log = mongoose.model('Log');
log
.where("user", req.session.user)
.desc("timestamp")
.populate("uarticle")
.populate("uarticle.article")
.run(function (err, articles) {
if (err) {
    console.log(err);
        res.send(500);
    return;
}
res.json(articles);

As you can see, I want mongoose to populate the "uarticle" field from the Log collection and, then, I want to populate the "article" field of the UserArticle ("uarticle").

But, using this code, Mongoose only populates "uarticle" using the UserArticle Model, but not the article field inside of uarticle.

Is it possible to accomplish it using Mongoose and populate() or I should do something else?

Thank you,

回答1:

From what I've checked in the documentation and from what I hear from you, this cannot be achieved, but you can populate the "uarticle.article" documents yourself in the callback function.

However I want to point out another aspect which I consider more important. You have documents in collection A which reference collection B, and in collection B's documents you have another reference to documents in collection C.

You are either doing this wrong (I'm referring to the database structure), or you should be using a relational database such as MySQL here. MongoDB's power relies in the fact you can embed more information in documents, thus having to make lesser queries (having your data in a single collection). While referencing something is ok, having a reference and then another reference doesn't seem like you're taking the full advantage of MongoDB here.

Perhaps you would like to share your situation and the database structure so we could help you out more.

回答2:

You can use the mongoose-deep-populate plugin to do this. Usage:

User.find({}, function (err, users) {
   User.deepPopulate(users, 'uarticle.article', function (err, users) {
      // now each user document includes uarticle and each uarticle includes article
   })
})

Disclaimer: I'm the author of the plugin.

回答3:

I faced the same problem,but after hours of efforts i find the solution.It can be without using any external plugin:)

    applicantListToExport: function (query, callback) {
      this
       .find(query).select({'advtId': 0})
       .populate({
          path: 'influId',
          model: 'influencer',
          select: { '_id': 1,'user':1},
          populate: {
            path: 'userid',
            model: 'User'
          }
       })
     .populate('campaignId',{'campaignTitle':1})
     .exec(callback);
    }

回答4:

how about something like:

populate_deep = function(type, instance, complete, seen)
{
  if (!seen)
    seen = {};
  if (seen[instance._id])
  {
    complete();
    return;
  }
  seen[instance._id] = true;
  // use meta util to get all "references" from the schema
  var refs = meta.get_references(meta.schema(type));
  if (!refs)
  {
    complete();
    return;
  }
  var opts = [];
  for (var i=0; i<refs.length; i++)
    opts.push({path: refs[i].name, model: refs[i].ref});
  mongoose.model(type).populate(instance, opts, function(err,o){
    utils.forEach(refs, function (ref, next) {
      if (ref.is_array)
        utils.forEach(o[ref.name], function (v, lnext) {
          populate_deep(ref.ref_type, v, lnext, seen);
        }, next);
      else
        populate_deep(ref.ref_type, o[ref.name], next, seen);
    }, complete);
  });
}

meta utils is rough... want the src?

来源：https://stackoverflow.com/questions/8543940/mongoose-populate-a-populated-field

标签

mongodb

node.js

mongoose

populate