Mongoose populate sub-sub document

Question

I have this setup in my MongoDB

Items:

title: String
comments: [] // of objectId's

Comments:

user: ObjectId()
item: ObjectId()
comment: String

Here's my Mongoose schema:

itemSchema = mongoose.Schema({
    title: String,
    comments: [{ type: Schema.Types.ObjectId, ref: 'comments' }],
});

Item = mongoose.model('items', itemSchema);

commentSchema = mongoose.Schema({
    comment: String,
    user: { type: Schema.Types.ObjectId, ref: 'users' },
});

Comment = mongoose.model('comments', commentSchema);

This is where I get my items along with the comments:

Item.find({}).populate('comments').exec(function(err, data){
    if (err) return handleError(err);
    res.json(data);
});

How do I populate the comments array with it's respective user? Since each comment has a user ObjectId()?

Answer 1

As a complete example calling populate on the result objects:

Item.find({}).populate("comments").exec(function(err,data) {
    if (err) return handleError(err);

    async.forEach(data,function(item,callback) {
        User.populate(item.comments,{ "path": "user" },function(err,output) {
            if (err) throw err; // or do something

            callback();
        });
    }, function(err) {
        res.json(data);
    });

});

The call to .populate() in the form invoked from the model takes either a document or an array as it's first argument. So you loop through the returned results for each item and call populate this way on each "comments" array. The "path" tells the function what it is matching.

This is done using the "async" version of forEach so it is non-blocking, but generally after all the manipulation all of the items in the response are not only populated with comments but the comments themselves have the related "user" details.

Answer 2

One more way (easier) to do this:

Item
  .find({})
  .populate({
	path:     'comments',			
	populate: { path:  'user',
		    model: 'users' }
  })
  .exec(function(err, data){
    if (err) return handleError(err);
    res.json(data);
});

Answer 3

Simpler

Item
  .find({})
  .populate({
    path: 'comments.user',
    model: 'users' }
  })
  .exec(function(err, data){
    if (err) return handleError(err);
    res.json(data);
});

Answer 4

To add one final method that people may want to use to select only particular fields from sub-documents, you can use the following 'select' syntax:

  Model.findOne({ _id: 'example' })
    .populate({ 
      path: "comments", // 1st level subdoc (get comments)
      populate: { // 2nd level subdoc (get users in comments)
        path: "user",
        select: 'avatar name _id'// space separated (selected fields only)
      }
    })
    .exec((err, res) => { 
        // etc
     });

Answer 5

To populate sub-sub document and populate from multiple schemas

ProjectMetadata.findOne({id:req.params.prjId})
.populate({
    path:'tasks',
    model:'task_metadata',
    populate:{
        path:'assigned_to',
        model:'users',
        select:'name employee_id -_id' // to select fields and remove _id field

    }
})
.populate({
    path:'client',
    model:'client'
})
.populate({
    path:'prjct_mgr',
    model:'users'
})
.populate({
    path:'acc_exec',
    model:'users'
})
.populate({
    path:'prj_type',
    model:'project_type'
}).then ( // .. your thing

or you can do it in following manner ..

   ProjectMetadata.findOne({id:req.params.prjId})
    .populate(
        [{
        path:'tasks',
        model:TaskMetadata,
        populate:[{
            path:'assigned_to',
            model:User,
            select:'name employee_id'
        },
        {
            path:'priority',
            model:Priority,
            select:'id title'
        }],
        select:"task_name id code assign_to stage priority_id"
    },
    {
        path:'client',
        model:Client,
        select:"client_name"
    },
    {
        path:'prjct_mgr',
        model:User,
        select:"name"
    },
    {
        path:'acc_exec',
        model:User,
        select:'name employee_id'
    },
    {
        path:'poc',
        model:User,
        select:'name employee_id'
    },
    {
        path:'prj_type',
        model:ProjectType,
        select:"type -_id"
    }

])

I found the second method (of using array) more useful when I had to get multiple sub-sub documents of same parent.

Answer 6

I use this:

.populate({
            path: 'pathName',
            populate: [
                {
                    path: 'FirstSubPathName',
                    model: 'CorrespondingModel',
                },
                {
                    path: 'OtherSubPathName',
                    model: 'CorrespondingModel',
                },
                {
                    path: 'AnotherSubPathName',
                    model: 'CorrespondingModel',
                },
            ]
        });

it's the more easier way that i find to do this.I expect to help. :)

Answer 7

do it try it`s working find Project and get project related populate Task and Perticular Task User find

db.Project.find()
.populate({
    path: 'task',
    populate: { path: 'user_id'}
})
.exec(async(error,results)=>{

})

Answer 8

Check the screenshot below. This thing works like charm!!!

Answer 9

This worked for me:

i.e. no need for model

    .populate({
      path: 'filters',
      populate: {
        path: 'tags',
        populate: {
          path: 'votes.user'
        }
      }
    })
    .populate({
      path: 'members'
    })