DivergentArrayError in mongoose while updating array of referenced docs - node.js

Question

I have a schema defined in mongoose as follow:
var VolunteerSchema = new Schema ({
......
other fields
.....
preferLocations:[{
type: Schema.ObjectId,
ref: 'Location'
}]
.....
});
I am using volunteer.save() method to update the model.
While updating to volunteer model i get the error as follow:
{ [DivergentArrayError: For your own good, using `document.save()` to update an
array which was selected using an $elemMatch projection OR populated using skip,
limit, query conditions, or exclusion of the _id field when the operation resul
ts in a $pop or $set of the entire array is not supported. The following path(s)
would have been modified unsafely:
preferLocations
Use Model.update() to update these arrays instead.]
message: 'For your own good, using `document.save()` to update an array which
was selected using an $elemMatch projection OR populated using skip, limit, quer
y conditions, or exclusion of the _id field when the operation results in a $pop
or $set of the entire array is not supported. The following path(s) would have
been modified unsafely:\n preferLocations\nUse Model.update() to update these a
rrays instead.',
name: 'DivergentArrayError' }
While updating the location I collect the _ids field in array and asigned to preferLocations as given below:
volunteer.preferLocations = locationIdsArray;
I don't get the error when I remove this line.What am I doing wrong?

Answer 1

When using $elemMatch in a projection, do not use document.save(). Instead, manually update your document using Model.update(). In your case you should try
volunteer.findOneAndUpdate(
{
_id: ObjectId("567452bae5b25d6e6c1a0f7e"),
localization: { '$elemMatch': { language: 'de' } }
},
{
$set: { 'localization.$.name' : "Neuer Name" }
}).exec(//...
});
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