Mapping arrays with duplicate values mangles the array about knockout.mapping HOT 5 CLOSED

The result is kind of unexpected. It is by design that the mapping plugin cannot handle arrays with duplicate objects (see the key callback part of the mapping plugin documentation).

For an array of primitives like you have here, I guess duplicates should be allowed.

Is your use-case with an array of primitives like in your example, or are you using objects?

from knockout.mapping.

The example I posted is a simplification but yeah, it matches my use case almost exactly. Here's a closer example:

data = {
  ...
  properties: {
    arrayKey: ["1", "1", "1", "2"]
  }
}

I'm grabbing a bunch of data via api, and the array that I noticed this happening on is one of a handful of properties that's stored in a serialized object. Until now we've been able to infer what we need from the length of the array and it's contents. It should be possible to rework things on the back-end and add a key, but being able to bind the existing array would be much easier for now.

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Ok! Well, if you have the time to create a pull request that would be highly appreciated :) Otherwise it may take a few days before I can get around to fixing it.

from knockout.mapping.

Alright. I'll see what I can do.

from knockout.mapping.

I haven't had a lot of time to look at this, but I've found that the culprit is line 305:

var index = ko.utils.arrayIndexOf(ko.utils.unwrapObservable(rootObject), item);

What happens is ko.utils.arrayIndexOf() returns the first matching index, which means that when the next line fires...

newContents[index] = mappedItem

...the same index gets used, so that item in the newContents array gets written over again and again. But since the mapping plugin is using ko.utils.arrayIndexOf I'm not sure how to proceed.

from knockout.mapping.