mongoose: Removing subdocument's content

Question

I have a Mongoose (using current version) schema with a subdocument:

var mySchema = new Schema({
  subdocument: { property1: { type: String } }
});
var myModel = mongoose.model('My-Model', mySchema);

Now I'm trying to update an existing document and to remove the subdocument like so using doc.subdocument = {}:

new myModel({ name: 'test', subdocument: { property1: 'test' }}).save(function(err, doc) {
  console.log('saved doc:\n', doc);
  doc.subdocument = {}; // remove content of subdocument
  doc.save(function(err, doc) {
    console.log('updated doc:\n', doc); // subdocument: null
    myModel.findById(doc._id, function(err, doc) {
      console.log('retrieved doc:\n', doc); // subdocument: { property1: 'test' }
      mongoose.disconnect();
    });
  });
});

The callback in doc.save returns the document with subdocument: null, so I assumed, the update worked as expected. However, when examining the database, the subdocument's content is still there -- this can be seen by above's sample code when I retrieve the document again.

The document in the DB looks as:

{ subdocument: { property1: 'test' }, __v: 0, _id: 57593a8130f2f7b6a12886b1 }

Is this a bug or a fundamental misunderstanding?

robertklep · Accepted Answer · 2016-06-09 10:28:39Z

2

I believe that regular JS object properties in schema are given a Mixed schema type by Mongoose.

For these types of properties, if they change, you need to explicitly tell Mongoose about that change before saving:

doc.subdocument = {};
doc.markModified('subdocument');
doc.save(...);

The "updated doc" will not reflect the document as it's stored in the database, only how it's represented in memory (it's simply another reference to the doc object).

As an alternative to .save(), you can also use findByIdAndUpdate(), with the added advantage that you can make it return the updated (stored-in-the-database) document using the new option:

myModel.findByIdAndUpdate(doc._id, {
  $set : { subdocument : {} }
}, { new : true }, function(err, doc) {
  // `doc` will now reflect what's stored in the database
});

edited Jun 9, 2016 at 10:28

answered Jun 9, 2016 at 10:13

robertklep

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2 Comments

qqilihq Over a year ago

Thank you, markModified does the trick! And especially thanks about the note of the returned doc document. Until now I had naively assumed that this was the document as stored in the database, so I'll have to review my code carefully.

robertklep Over a year ago

@qqilihq see my edit, I added an alternative to save that might be useful as well.

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