toJS returns empty object in array after splice about knockout.mapping HOT 8 CLOSED

This is due to the way the plugin stores which items have already been mapped and which have not been mapped (inside the __ko_mapping__ property in mappedObject).

The idea is that if you want to add new items you would do this through an update with fromJS or by using mappedCreate.

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I see. So is it possible to change the order of an observable array created with fromJS? Should I not be using the splice, sort, push, etc. methods when using the mapping plugin?

I tried mappedObject.items.mappedCreate({name: 'item 4'}); to add an item, but it exhibited the same issue. mappedObject.items.push(ko.mapping.fromJS({name: 'item 4'})); seems to work, but I'm not sure if that's the right way to do it.

Thanks for your help,
Bill

from knockout.mapping.

Your 'workaround' using fromJS is completely valid and that's pretty much the intended use. However, when you splice in a copy of another mapped object then the system gets confused. In your workaround however you are creating a new mapped object and inserting that. That should work fine.

The mappedCreate is a convenience function that only works when you have a create callback, otherwise it inserts your unmapped object in the array. That's odd behavior and I'm thinking about removing this functionality entirely.

Does that make things a bit clearer?

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Thanks. That's very helpful. My only other question then is - is there a safe way to move an item from one position to another without confusing the system? That's originally what I was trying to accomplish using the knockout-sortable plugin.

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To be honest I'm also currently using the sortable plugin without any of these issues, which makes it doubly odd.

However, the difference is that I'm using the create callback to create the separate items in my array, like so:

var mapping = {
  items: {
    create: function(data) {
      return new MyItem(data.data);
    }
  }
};

Maybe you could give that approach a shot, just as a test?

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Thanks for the tip! That works perfectly! I modified my original example using the sortable plugin to use the create callback and that small change fixed the problem.

Original version (does not work): http://jsfiddle.net/WDrep/2/
Modified version (with create callback): http://jsfiddle.net/WDrep/11/

I would have never thought that would make a difference. Thanks for your help!

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You're welcome!

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I didn't see this issue when I commented on #65.

On the mappedCreate callback, and perhaps the push itself, we could wrap the value inserted into the array by default with a call to ko.mapping.fromJS(). This isn't super elegant, but it would fix any confusion with adding objects to mapped arrays.

It would cause any object added to a mapped array to behave "as expected" in that the full object added would always get returned, instead of returning an empty object.

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