CODEWITHSUNDEEP
node.jsmongodbmongooseaggregation-framework
Rohit Lala
Rohit Lala

Reputation: 277

Mongoose Virtuals in MongoDB Aggregate

My Mongoose Schema is as follows: 

var DSchema = new mongoose.Schema({
  original_y: {type: Number},,
  new_y: {type: Number},,
  date: {type: Date},
  dummy: [dummyEmbeddedDocuments]
  }, toObject: { virtuals: true }, toJSON: { virtuals: true}
});

DSchema.virtual('dateformatted').get(function () {
 return moment(this.date).format('YYYY-MM-DD HH:mm:ss');
});

module.exports = mongoose.model('D', DSchema);

A document in my schema would be the following: 

{
 id:1,
 original_y: 200,
 new_y: 140,
 date: 2015-05-03 00:00:00.000-18:30,
 dummy: [
  {id:1, storage:2, cost: 10},
  {id:2, storage:0, cost: 20},
  {id:3, storage:5, cost: 30},
  ]
}

My Query: 

Item.aggregate([
{ 
    "$match": {
        "dummy.storage": {"$gt": 0}
    } 
},
{ 
    "$unwind": "$dummy"
},
{
    "$project": {
        "original_y": 1, 
        "new_y": 1,
        "dateformatted": 1,
        "dummy.id": "$dummy.id",
        "dummy.storage": "$dummy.storage",
        "dummy.cost": "$dummy.cost",
        "dummy.tallyAmount": {
            "$divide": [
                { "$add": ["$new_y","$original_y"] },
                "$dummy.cost"
            ]
        }
    }
},
{
    "$group": {
        "_id": "_$id",
        "original_y": { "$first": "$original_y" },
        "dateformatted": { "$first": "$dateformatted" },
        "new_y": { "$first": "$new_y" },
        "dummy": {
            "$addToSet": "$dummy"
        }
    }        
}
]).exec(callback);

This query however returns the VIRTUAL dateformatted attribute as NULL. Any thoughts as to why this is happening?

Upvotes: 16

Views: 12728

Answers (4)

Joseito Fernandes
Joseito Fernandes

Reputation: 111

Here's a solution that works! Aggregate queries return js objects which is not an instance of mongoose Document. You may use Model.hydrate

const documents = docs.map(doc => myModel.hydrate(doc))

Upvotes: 2

Fraction
Fraction

Reputation: 12954

the <field>: <1 or true> form is used to include an existing field which is not the case here since the dateformatted field doesn't exist and you have to create it using an expression, $dateToString can be used:

"$project": {
  "original_y": 1, 
  "new_y": 1,
  "dateformatted": { "$dateToString": { "format": "%Y-%m-%d %H:%M:%S", "date": "$date" } },
  ...

Another option is to use it with $addFields:

{
  "$project": {
    ...
  }
},
{
  "$addFields": {
    "dateformatted": { "$dateToString": {"format": "%Y-%m-%d %H:%M:%S", "date": "$date"} }
  }
},
...

Upvotes: 0

bendataclear
bendataclear

Reputation: 3850

This is an old question but I've come up with a useful hack to get back the virtuals and thought it might be useful for those searching for this problem.

You can easily convert the objects back to mongoose models:

documents = documents.map(d => {
  return new Document(d);
});

var virtual = documents[0].virtualProperty;

Upvotes: 10

JohnnyHK
JohnnyHK

Reputation: 311865

A couple notes in the docs touch on why this is so:

  • Arguments are not cast to the model's schema because $project operators allow redefining the "shape" of the documents at any stage of the pipeline, which may leave documents in an incompatible format.
  • The documents returned are plain javascript objects, not mongoose documents (since any shape of document can be returned).

But it goes beyond this because the aggregate operation is performed server-side, where any client-side Mongoose concepts like virtuals do not exist.

The result is that you'll need to include the date field in your $project and $group stages and add your own dateformatted field to the results in code based on the date values.

Upvotes: 12

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