Set array element to null with Mongoose

Question

I'm encountering an interesting problem, trying to set to null an element of a sub-array in mongo with mongoose (wich seems ridiculously obvious, yep).

My Schema looks like :

var ItemSchema = new Schema({
  name : String,
  slots: { type: [{ type : Schema.Types.ObjectId, ref: 'Slot' }], default: [] }
});

My data looks like :

{
  _id  : ObjectId("53bafbfd00cbcc3a1178e11b"),
  name : "item 1",
  slots: [null, null, ObjectId("53baf297d63228631029d2f8"), null, null]
},
{
  _id  : ObjectId("53baf297d63228631029d2f8"),
  name : "item 2",
  slots: [ObjectId("53baf1b3fecfe25c10233801"), null, null, null, null]
}

nb: the nullvalues are important for order logical purposes.

So, let's imagine I get the first of these items :

Items.findById('53bafbfd00cbcc3a1178e11b', function (err, item) {

  console.log(item.slots);
  // [null, null, "53baf297d63228631029d2f8", null, null] --> OK

  // BIG update here
  item.slots[2] = null;

  item.save(function (err, itemSaved) {

    // no errors

    console.log(itemSaved.slots);
    // [null, null, null, null, null] --> Well, so everything works, right ?

    // so let's find the same item again !

    Items.findById('53bafbfd00cbcc3a1178e11b', function (err, itemSearched) {

      console.log(itemSearched.slots);
      // [null, null, "53baf297d63228631029d2f8", null, null] --> what ?? id still here ?

    });

  });

});

So the id isn't set to null even if save worked.. I don't get it, really. I need so much an explanation ! Thanks in advance.

can you try console.logging item.save(function (err, itemSaved) { the itemSaved ? — tpae
– tpae, Commented Jul 7, 2014 at 20:44
I updated my question in this way : saved item looks ok, but not after the last Find query.. — meriadec
– meriadec, Commented Jul 7, 2014 at 20:56
I ran into this a while ago, actually. item.save sometimes does not call update on changed values properly, if you actually step through using a debugger, you will see interesting stuffs. — tpae
– tpae, Commented Jul 7, 2014 at 21:34

JohnnyHK · Accepted Answer · 2014-07-07 21:54:03Z

4

It seems you need to explicitly mark that element as modified or save won't pick up the change:

item.slots[2] = null;
item.markModified('slots.2');
item.save(function (err, itemSaved) {
    ....

Perhaps because null is not a valid ObjectId.

The other way to do this is with update and $unset:

Items.update(
    {_id: '53bafbfd00cbcc3a1178e11b'},
    {$unset: {'slots.2': 1}}, function(err, numAffected) {
        ...

edited Jul 7, 2014 at 21:54

answered Jul 7, 2014 at 21:40

JohnnyHK

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2 Comments

tpae Over a year ago

Good solution, you can also just do item.markModified('slots') right?

JohnnyHK Over a year ago

@tpae That also works, but it's not as efficient as Mongoose then has to update the whole array instead of just the modified element.

tpae · Accepted Answer · 2014-07-07 21:42:00Z

2

Try this instead:

Items.update(
    {_id: '53bafbfd00cbcc3a1178e11b'}, 
    {$set: { slots: [null, null, null, null, null] } }, 
function(err, results) {
  Items.findById('53bafbfd00cbcc3a1178e11b', function (err, itemSearched) {
      console.log(itemSearched.slots);
    });
  });
});

Make a wrapper function around it, like this:

ItemSchema.statics.clearSlot = function(id, slot, cb) {
  var self = this;
  this.findById(id, function(err, item) {
    var slots = item.slots;
    slots[slot] = null;
    self.update({_id: id}, {$set: {slots: slots}}, cb);
  });
});

Something like that. lol

Call it like

Item.clearSlot(id, 2, function(err, updated) {

edited Jul 7, 2014 at 21:42

answered Jul 7, 2014 at 21:30

tpae

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1 Comment

meriadec Over a year ago

Sry, but it's not exactly what I search. I need to set one element of the 'slots' array to null, not to reset it to its blank state (not sure if I explain well ^^)

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