Mongoose: deep population (populate a populated fi

问题:

I have Category model:

Category:
    ...
    articles: [{type:ObjectId, ref:'Article'}]

Article model contains ref to Account model.

Article:
    ...
    account: {type:ObjectId, ref:'Account'}

So, with populated articles Category model will be:

{ //category
    articles: //this field is populated
     [ { account: 52386c14fbb3e9ef28000001, // I want this field to be populated
         date: Fri Sep 20 2013 00:00:00 GMT+0400 (MSK),
         title: 'Article 1' } ],
    title: 'Category 1' }

The questions is: how to populate subfield (account) of a populated field ([articles])? Here is how I do it now:

globals.models.Category
    .find
        issue : req.params.id
        null
        sort:
            order: 1
    .populate("articles") # this populates only article field, article.account is not populated
    .exec (err, categories) ->
        console.log categories

I know it was discussed here: Mongoose: Populate a populated field but no real solution was found

回答1:

Mongoose has now a new method Model.populate for deep associations:

https://github.com/LearnBoost/mongoose/issues/1377#issuecomment-15911192

回答2:

Firstly, update mongoose 3 to 4 & then use the simplest way for deep population in mongoose as below :

Suppose you have Blog schema having userId as ref Id & then in User you have some review as ref Id for schema Review. So Basically, you have three schema : 1. Blog 2. User 3. Review

And, you have to query from blog, which user owns this blog & the user review. So you can query your result as :

<BlogModel>.find({}).populate({path : 'userId', populate : {path : 'reviewId'}}).exec(function (err, res) {

 })

回答3:

Populating across multiple levels

Say you have a user schema which keeps track of the user's friends.

var userSchema = new Schema({
  name: String,
  friends: [{ type: ObjectId, ref: 'User' }]
});

Populate lets you get a list of a user's friends, but what if you also wanted a user's friends of friends? Specify the populate option to tell mongoose to populate the friends array of all the user's friends:

User.findOne({ name: 'Val' }).populate({
    path: 'friends',
    // Get friends of friends - populate the 'friends' array for every friend
    populate: { path: 'friends' }
});

Reference: http://mongoosejs.com/docs/populate.html#deep-populate

回答4:

It might be a bit too late, but I wrote a Mongoose plugin to perform deep population at any arbitrary nested levels. With this plugin registered, you can populate category's articles and accounts with just a single line:

Category.deepPopulate(categories, 'articles.account', cb)

You can also specify populate options to control things like limit, select... for each populated path. Checkout the plugin documentation for more information.

回答5:

Easiest way to accomplish this in 3.6 is to use Model.populate.

User.findById(user.id).select('-salt -hashedPassword').populate('favorites.things').exec(function(err, user){
    if ( err ) return res.json(400, err);

    Thing.populate(user.favorites.things, {
        path: 'creator'
        , select: '-salt -hashedPassword'
    }, function(err, things){
        if ( err ) return res.json(400, err);

        user.favorites.things = things;

        res.send(user.favorites);
    });
});

回答6:

Sorry to burst your bubble, but there's not a directly supported solution to this. As for Github issue #601, it looks grim. According to the 3.6 release notes, it looks like the developers acknowledged the issue are happy with manual recursive/deep population.

So from the release notes, the recommended method is to nest populated calls in the callback, so in your exec() function, use categories.populate to further populate before sending a response.

回答7:

globals.models.Category.find()
  .where('issue', req.params.id)
  .sort('order')
  .populate('articles')
  .exec(function(err, categories) {

    globals.models.Account.populate(categories, 'articles.account', function(err, deepResults){

      // deepResult is populated with all three relations
      console.log(deepResults[0].articles[0].account);

    });
});

The following example is inspired by the question asked @codephobia and populates two levels of many relationships. First fetch a user, populate its array of related orders and include each orderDetail.

user.model.findOne()
  .where('email', '***@****.com')
  .populate('orders')
  .exec(function(err, user) {

    orderDetail.model.populate(user, 'orders.orderDetails', function(err, results){

      // results -> user.orders[].orderDetails[] 
    });
});

This works fine in 3.8.8 but should work in 3.6.x.

回答8:

This concept is deep Population. Here Calendar,Subscription,User,Apartment are mongoose ODM models in different levels

Calendar.find({}).populate({
      path: 'subscription_id',model: 'Subscription',
         populate: {path: 'user_id',model: 'User',
           populate: {path: 'apartment_id',model: 'Apartment',
              populate: {path: 'caterer_nonveg_id',
                          model: 'Caterer'}}}}).exec(function(err,data){ 
                          if(!err){
                             console.log('data all',data)
                           }
                           else{
                             console.log('err err err',err)
                            }
                   });