updateFromJS broken?

[abp]

Hi,

i'm trying to use updateFromJS to merge data back into a fairly complex viewModel after the data is saved and probably changed on the server.

But it seems updateFromJS is replacing all the data instead of merging. I thought it would merge. So, am i doing something wrong or is it broken?

Here's a sample test case:
http://jsfiddle.net/rBRJZ/2/

[sagacity]

Hi abp,

This is by design. Basically, the model you pass to updateFromJS represents the 'current state' of your model that comes from your server. The mapping plugin then takes this current state and updates your mapped viewModel to match this state, so that your GUI also shows the current state.

In your example, therefore, it would remove the elements with keys '1' and '3' since they are not in your 'current state'. In a real-life scenario, maybe this is because some other user deleted items #1 and #3 since the last update occured.

If you want to do regular merging, that would be something you'd have to do yourself, manually.

I hope this explains why you are seeing this behavior. If not, feel free to reopen this ticket :)

[abp]

Sure, answers my question right to the point. Sorry for reporting a bug on this. :)
Since my model is complex and rendering everything again would take far to much time i will code some simple merging by myself.

[sagacity]

No, that's okay! When writing your merge code, please note there's a useful "ko.utils.compareArrays" available that allows you to do diffs of two arrays. That can be a good starting point for you, I think.

[abp]

Thanks for the hint, but now i already have a dead simple remove/add based merging. Will see how it works out. :)

[sagacity]

Excellent! Good luck :)