*Feature Request* Use fields in Populate Virtuals

[florianbepunkt]

It would be useful for some use cases to set the references in populated virtuals based on existing fields in the doc, if this is possible. See the following example. If the field internalOrderId in the Refund document is no null, it uses sourceOrderId as localField, if it is null, it uses _id.

You can do something similar already when you populate fields using a dynamic ref, but since I can't use the _id field as reference this is not an option. As far as I know, you can't do the same when you use populate virtuals.

RefundSchema.virtual('order', {
  ref: 'Order',
  localField: (this.internalOrderId !== null) ? 'sourceOrderId' : 'internalOrderId',
  foreignField: (this.internalOrderId !== null) ? 'sourceId' : '_id',
  justOne: false
});

[vkarpov15]

I like this idea, should be doable, will investigate for next minor release.

[florianbepunkt]

@vkarpov15 We just updated our mongoose version and I tried to get this to work. Could you please add the syntax to the documentation or provide a basic example?

I have this but it throws an error TypeError: Invalid path. Must be either string or array

Baiscally what I try to accomplish here is to set the virtual dynamically based on a field of the source document (RefundSchema)

RefundSchema.virtual('order', {
  ref: 'Order',
  localField: function() {
    if (this.internalOrderId) {
      return this.internalOrderId;
    } else {
      return this.sourceOrderId;
    }
  },
  foreignField: function() {
    if (this.internalOrderId) {
      return this._id;
    } else {
      return this.sourceId;
    }
  },
  justOne: function() {
    if (this.internalOrderId) {
      return true;
    } else {
      return false;
    }
  },
});

EDIT: Is it by any chance that the foreignField does not support documents _id field?

[florianbepunkt]

Okay, I figured out the syntax but there seems to be a bug.... I have the following virtual with dynamic localField and foreignField

RefundSchema.virtual('order', {
  ref: 'Order',
  localField: function() {
    if (this.internalOrderId) {
      // CASE A
      return 'internalOrderId';
    } else {
      // CASE B
      return 'sourceOrderId';
    }
  },
  foreignField: function() {
    if (this.internalOrderId) {
      // CASE A
      return '_id';
    } else {
      // CASE B
      return 'sourceId';
    }
  },
  justOne: false,
});

Now I have two queries that produce inconsistent results:

// QUERY A - returns doc with _id 5a317e080732e735527911fe whic is CASE A for sure
Refund.find({_id: '5a317e080732e735527911fe'}).populate('order').exec().then((resp) => {
  console.log(JSON.stringify(resp, null, 3));
})

// QUERY B - should return CASE A docs and CASE b docs
Refund.find({}).populate('order').exec().then((resp) => {
  console.log(JSON.stringify(resp, null, 3));
})

Actual Behaviour
Query A does populate the order field. However Query B returns (amongst others) the document from Query A (5a317e080732e735527911fe), but does not populate the order field

Expected Behaviour
Both queries should populate the order field for document 5a317e080732e735527911fe

[vkarpov15]

Thanks for reporting @florianbepunkt , will investigate

[vkarpov15]

Thanks for your patience @florianbepunkt , we really kicked this issue very far down the road. The issue should be fixed in 5.2.18.