Updating a subfield in a mongoDB document using findOne and save

Question

I'm trying to update a particular subfield in a mongoDB document and have decided to first find the object in question and then save an updated one. For some reason, the save option seems to ignore my changes.

I have one object in my collection, and it meets the following schema:

var tschema= mongoose.Schema({
a: Object
})

var t = db.model('tongoose',tschema);
t.findOne({},function(err,obj){
  console.log(obj.a); //yields ['banana',3]     
  obj.a[1]=1; //to make ['banana',1]
  console.log(obj); //yields ['banana',1]

  obj.save(function(err,real){
    console.log(real); //yields ['banana',1]
  });
});

But when I go back to the mongoDB and look up the saved object, it never shows any changes. Can you spot what I'm doing wrong?

Much appreciated.

Answer 1

Because your schema defines a as a generic object, that field is treated as the Mixed type by Mongoose and you need to mark it as changed by calling markModified or save will ignore the change.

obj.markModified('a');
obj.save(function(err,real){ ...

See the discussion of Mixed types on this page of the docs.